CA2008485A1 - Selective interference light filter - Google Patents
Selective interference light filterInfo
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- CA2008485A1 CA2008485A1 CA 2008485 CA2008485A CA2008485A1 CA 2008485 A1 CA2008485 A1 CA 2008485A1 CA 2008485 CA2008485 CA 2008485 CA 2008485 A CA2008485 A CA 2008485A CA 2008485 A1 CA2008485 A1 CA 2008485A1
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- layer structure
- light filter
- radiation
- interference light
- layers
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Abstract
SELECTIVE INTERFERENCE LIGHT FILTER
A b s t r a c t The light filter has a layer structure wherein layers reflect directional luminous radiation and are equidistant with the refractive index varying periodi-cally in depth. The layers are formed by exposing to monochromatic radiation at a predetermined wavelength an element made of a light-sensitive material trans-parent to said radiation and placed in front of a mir-ror only during the emission of radiation. In an opti-cal instrument a selective element may be said light filter installed in a manner allowing its turn relati-ve to luminous radiation directed thereto.
A b s t r a c t The light filter has a layer structure wherein layers reflect directional luminous radiation and are equidistant with the refractive index varying periodi-cally in depth. The layers are formed by exposing to monochromatic radiation at a predetermined wavelength an element made of a light-sensitive material trans-parent to said radiation and placed in front of a mir-ror only during the emission of radiation. In an opti-cal instrument a selective element may be said light filter installed in a manner allowing its turn relati-ve to luminous radiation directed thereto.
Description
~ield of the Invention The present invention relates to optical instru-ments, more particularly, to selective interference light filters and optical instruments, in which they are used, The invention may be advantageously used in spect-roscopy, lighting engineering, laser and optical instru-ment making and also in space exploration.
Background Art There are known interference light filters comp-rising two or more groups of alternating layers of di-electric material with different refractive index, which have an optical thickness equal to a quarter wave of luminous flux directed to said light filter (cf. SU, A, 539,284; SU, A, 881,647).
Production of such filters generally involves un-wanted complexities. Moreover, the necessary protective coatings further complicate the manufacturing pro-cess and impair optical properties of said filters, that is, transmission of radiation.
Also, chemically pure materials may be required in production of the afore-mentioned filtersO
In the known light filters a wavelength may be continuously changed only within narrow limits.
~here are also known selective interference light filters having a layer structure wherein each layer reflects lurninous flow directed to said light 2~ 3s filter. The layer structure is formed with a dielect-ric layer deposited on a metal base and having a phase hal~-width multiple of ~ and with an even number of alternating quarter-wave layers of two dielectric 5 materials with high and low refractive index. Such a combination of layers is topped with an absorbing metal film whose thickness is much smaller than the operating wavelength (cf. Optika i spec~roskopiya, Volume ~0, 1976, Nauka publishers, ~eningrad, Goldina N,D. and ~roitsky J~.~., pp 935 - 938~.
Such a light filter reflects not only the select-ed wavelength but also other wavelengths beyond the reflection band, which are treated as interference.
Moreover, said light filters have essentially the same disadvantages as the light filters discussed pre-viously.
Briei De~cription of the I~vention It is an object of the present invention tocreate ~ selective interference light filter which would make it possible to continuously adjust, within wide limits, the operating wavelength in the event of variations of the angle of incidence of luminous flux.
Another object of the invention is to provide essentially without change, as compared with the prior art, the lightfilter spectral bandwidth, reflec-tion factor and contrast.
2 ~ 8 S
Still another object of the invention is to de-crease incident radiation background.
Yet another object of the invention is to increase further the continuous adjustment range.
A further object of the invention is to orovide a light filter capable of identifying a radiation spec-trum of various substances.
One more object of the invention is to create a light filter separating several spectral bands with dif-10 ferent wavelengths at the same time.
There is provided a selective interference light filter having a layer structure wherein each layer reflects luminous radiation direc'ed to the light fillter, in which, according to the invention, the 15 layers comprised in the layer structure are equidis-tant with the refractive index varyinp~ periodically in depth and are formed by exposing to at least one mono-chromatic radiation at a predetermined wavelength an element made of a light-sensitive material transpa-20 rent to said radiation and placed in front of a mirroronly during the emission of radiation.
As distinct from the known interference light filters formed by vacuum deposition of plane-parallel layers of pure materials, the proposed light filter 25 allows continuous adjustment of the operating wave-length within fairly wide limits.
The layer structure reflects different wavelengths, s depending on the angle of incidence of light directed to said structure.
The adjustment range of a wavelength reflected from the layer structure depends on effective refrac-tive index of said structure. More specifically, thegreater is the refractive index, the narrower is the adjustment range. On the other hand, the greater the number of layers forming the structure and the greater the dif~erence between their refractive indexes, the higher i9 the refractive index and the narrower is the spectral band.
The irradiated element may be fabricated from photoemulsion based on salts of silver or bichromized gelatin or a photorecording polymeric medium or a photopolymerizing composition of materials.
~ ormed by vacuum deposition are normally not more than 30 to 40 layers. A further increase in the number of layers re~ults in more defects. ~herefore,the reflection factor will not be increased and the spect-ral band will not be narrower. To obtain agreat ref-lection factor and a narrow spectral band with a small number of layers, use should be made of materials characterized by a great difference between refractive indexeq n1 and n2. Since n1 may not be less than 1.3, n2 normally exceeds 2. As a result, the effective refractive index is about 2 or greater.
A method of manufacturing the proposed light s filterJ permits obtaining light filters with a greater number of layers, more specifically, with some 100 to 200 layers, the thickness thereof (equal to half a waveleneth) being provided automatically to a desired accuracy, The effective refractive index of the layer system remains close to the refractive index of the source light-sensitive material (about 1.5 in the case of photoemulsion based on salts of silver~. A greater number of layers ensures, at a low modulation level of the refractive index, a high reflection factor and a narrow spectral band (essentially similar to that of filters made by deposition), whereas a low effec-tive refractive index provides for a wide wavelength adjustment range.
It is preferable that the light filter accord-ing to the invention should comprise a base accommo-dating a layer structure. The light filter with a base accommodating a layer structure has the following advantages over the known light filter without a base:
greater strength due to the base strength, a higher reflection factor, a narrower spectral band and better contrast due to exclusion from interference of a beam reflected from the air-layer structure interface. Depending on the material of the base and the operating wavelength range, the base may be used to suppress interlerence pec~ks of orders higher than the first working order of interference.
~r~ 85 The base may comprise at least one prism with a layer structure disposed on its reflecting face and luminous radiation directed to any free face thereof. Also, the base may represent at least one op-5 tical wedge with a layer structure arranged on its oneface and luminous radiation directed to the other face thereof. In another embodiment of the invention the base may be an element in the form of a lens.
The light filter comprising a base in the form 10 of a prism increases the operating wavelength adjust-ment range.
An advantage of the light filter having a base formed with an optical filter over the light filter having a flat base is that the beam reflected from the 15 air-base interface is separated from interfering beams linearly and, in addition, has another direction, as in the ca~e of a base in the form of a prism. On the other hand, the light filter cDmprising a wedge has the 3ame advantage as the light filter having a flat 20 b~se, more specifically, smaller d~nensions and corres-pondence of inpu~ and output faces.
The light filter comprising a base in the fo~n of a lens acts both as an optical filter element and a focusing ele~ent.
When an element of a light-sensitive material is e~po~ d to two or more monochromatic radiations with different wavelengths, the layer structure may have, 2~
respectively, two or more combinations of equidistant layers, each of which corresponds to the natural wave-length of said monochromatic radiation.
Such a light filter is polychromatic. It reflects simultaneously two or more wavelengths, each of which is readjusted after a change in the angle of incidence of radiation affecting said light filter.
It is of advantage that combinations of equidis-tant layers in the layer structure should be arranged successively along luminous radiation directed to said layer structure. It is also advantageous that said layers should be spatially aligned.
Production of the proposed light filter is sub-stantially simplified as compared with the prior art light filter. Spatial alignment of combinations of equidistant layers makes it possible to obtain to a higher accuracy the relation between Preset wavelengths upon reflection since different combinations of layers are formed simultaneously.
It is also advantageous that two or more combina-tions of equidistant layers should be formed by paral-lel beams of monochromatic radiation, while the layer structure contains separate sections comprising combi-nations of equidistant layers corresponding to sepa-rate sections of the wave front of luminous radiation directed to said layer structure.
Spatially separated beams of different wavelengths 2~ s are produced by such a light filter upon reflection.
It i~ further advantageous that the layer struc-ture should comprise layers made equidistant in a cross-section of said layer structure in a plane 5 which is, at the same time, perpendicular to any layer and to the thickness variation direction thereof and is formed by radiation characterized by a continuous spectrum.
Such a light filter makes it possible to adjust the wavelength both by changing the angle of incidence of light directed to the light filter and by displacing said light filter linearly in the vicinity of a slit diaphragm. The proposed light filter is characterized by fairly simple production techniques, which is an apparent advantage over the known wedge light filter made by wedge vacuum deposition of layers of material.
The layer structure may include a compression means providing for a linear change in the thickness of equidistant layers along said layer structure.
Therefore, in production of the light filter provision is made for changing the refractive index by fairly simple means.
The prism may have a rhomboidal section with identical layer structures being disposed on its two symmetrical side faces.
The prism may also have two pairs of syrnmetrical side faces with a common symmetry ~lane. Each side 2~ s face of one paix may accommodate layer structures.
Such a light filter is selective, as regards the wavelength and the angle of incidence. It ref-lects luminous radiation at only one wavelength in a predetermined direction. Moreover, said light filter may have smaller dimensions and reduced w~ht due to omission of inoperative parts of the rhomboid.
To provide for accurate setting of a filtered wavelength and monitoring of the angle of incidence Of light directed to the layer structure, it is ad-visable that the light filter according to the inven-tion should comprise a case whose walls are provided with two holes adapted, respectively, to pass radia-tion to the layer structure and to release the filter-ed radiation.
The layer structure may be installed in thecase in a manner allowing its turn and/or linear displacement relative to the emitted radiation.
~ Vith such an arrangement, the outgoing filter-ed radiation is not restricted to said hole in thecase, a feature being of appreciable importance in embodiments of the light filter characterized by spatial displacement of filtered radiation.
~urthermore, the light filter forming the sub-ject of the present invention may comprise a case,one wall of which is formed by an input face of the prism or optical wedge, while the opposite wall of s said case accommodates a diaphragm suited to pass radiation to the layer structure, the layer structure and the diaphragm being disposed in a manner allowing relative turn and/or linear displacement.
Such filters permit scanning and/or directing the beRm and/or adjusting the reflected wavelength.
The proposed light filter ensures continuous variation of the operating wavelength and is charac-terized by a narrow spectral band, high contrast and high reflection factor.
Brief Description o$ the Drawings Other object~ and features of the invention will become apparent from the description of preferred embodiment thereof, taken in col~junction with the ac-companying drawings, wherein:
~ igure 1 shows a selective interference lightfilter according to the invention;
~ igure 2 showæ the same light filter comprising a base in the form of a prism according to the inven~
tion;
~ igure 3 shows the same light filter comprising a base in the form of an optical wedge according to the invention;
~ 'igure 4 shows the same light filter comprising a base in the form of a lens according to the in-vention;
~igure 5 depicts a light filter incorporating 2 ~ 8 S
several prisms according to the invention;
~ igure 6 depicts a light filter comprising several optical wedges according to the invention;
Figure 7 shows a light filter with combinations of layers disposed successively in the direction of radiation according to the invention;
~ igure 8 shows a light filter with spatially separated combinations of layers according to the invention;
~igure 9 shows a light filter with spatially aligned combinations of layers according to the invention;
~ igure 10 shows a light filter enabling conti-nuou~ adjustment of a filtered radiation wavelength according to the invention;
~ igure 11 depicts a light filter comprising means for compressing a layer structure according to the invention;
71'igure 12 shows the same light filter with comp-ressed layers according to the invention;
~ igure 13 shows a light filter with a basehaving a rhomboida]. section according to the inven-tion;
~ i~ure 1~ shows a light filter comprising a base whose section represents an isosceles triangle according to the invention;
~igure 15 sh~ws a light filter with an intrica-_ 12 X~ 'lB5 tely shaped base according to the invention;
Figure 16 shows a light filter comprising acase according to the invention; and Figure 17 shows another embodiment of the light filter comprising a case according to the invention.
Detailed Description of the Invention Referring to the drawings the selective inter-ference light filter forming the subject of the pre-sent invention comprises a layer structure 1 (Figure 1) made up of equidistant layers 2, 3, ~ and 5 with re-fractive index periodically varying in depth. Produc-tion of such a light filter-is diagrammatically illu~qt-rated in ~igure 1. A parallel lu~inous flux G is directed to an element of a suitable transparent ligh~
-sensitive material through an optical system 7, said flux comin~ from a light source 8. ~uring the emission of radiation, the irradiated element is Dlaced in front of a metallic mirror 9 which is removed on comDletion of the radiation process. Said element is exposed to at least one monochromatic radiation at a predetermined wavelength ~ , The wave of the luminuous flux 6 reflected from the mirror 9 interferes with the incident wave whereby standing waves are formed. The refractive index of the light-sensitive material changes differently at crests 10 and nodal points 11 of the standing waves.
After ex~osure to radiation, said element of 2~ 5 li~ht-sensitive material acquires the layer structu-re 1. The crests 10 of said waves located equidistant-ly in the irradiated element at a distance ~0~2n from one another (where n is the re~ractive index of the material) correspond to the equidistant layers 2 through 5 in the layer structure 1. So, the perio-dicity of the layers 2 through 5 and, consequently, the layer thickness d = ~ (1). Vertical lines 2n mark schematically a plane 12, in which variations of the refractive index of the light-sensitive mate-rial are maximal, The number N of the layers 2 through 5 in the layer structure 1 depends on thick-ness D of the irradiated element and on thickness d of each layer 2 through 5 and is defined by the equation D D-2n N = - Jlc (2~
Each layer 2 through 5 partially reflects lumi-nous radiation directed to the layer structure. In-terference of the beams reflected from the layers 2 throug~ 5 is maximal at a predermined wavelength equal to the dif~erence between lengths of interfer-ing beams, Radiation at said wavelength is filtered by the proposed light filter upon reflection.
The irradiated element is made of a suitable transparent light-sensitive material which may be Z ~ 5 photoemulsion based on salts of silver or bichromi-zed gelatin or a photorecording polymeric medium or a photopolymerizing composition of materials, The layer structure 1 comprises a base formed with a prism 13 (~igure 2~ or an optical wedge 14 (~igure 3) or a lens 15 (~igure 4~.
In the prism 13 (~'igure 2~, the layer structure 1 is disposed on a reflective face 16, while luminous radiation 17 is directed to any free face 18. ~iltered 10 radiation 19 comes out through another face 20 of the prism 13.
Similarly, the layer structure 1 is arranged on a face 21 (~igure 3) of the optical ~edge 14, the luminous radiation 17 is directed to its face 22, and 15 the filtered radiation 19 comes out through the same face 22.
When use is made of the lens 15 (~igure 4), the light filter is designed in a manner similar to that described above, It doe~ not only filter the radiation 20 17 but also brings it into a focus 23 of the lens 15 if the luminuous radiation 17 is collimated.
In all the embodiments described, radiation 24 (~igures 2 through 4~ reflected from the environ-ment-light filter interface has a direction diffe-25 rent from that of the filtered radiation 19.
The base may comprise more than one prism 13 orwedge 14, as illustrated in ~igures 5 and 6. Prisms ;~G~ ~8' 13' (and wedges 14'~ are arranged along the structu-re 1 and their number depends on the length of the structure 1. Each prism 13' has dimensions and, consequently, weight much smaller than those in the embodiment of ~igure 2, wherein only one prism 13 is utilized. The weight and dimensions of all the prisms 13' are smaller than the weight and dimensions of the prism 13.
Therefore, overall dimensions and total weight of the light filter of Figure 5 are substantially smaller than those in the embodiment of ~igure 2~ It may be asserted that the construction of the entire light filter is quasi-flat. The light filter is de-signed in much the same manner in another embodiment comprising a plurality of wedges 14' t~igure 6).
The irradiated element may be exposed to two or more radiations at different wavelengths. Combi.na-tions of equidistant layers corres~onding to said wavelengths are formed in the element. Said combina-tions of layers in the layer structure may be ar-ranged differently to suit particular functions and applications of the fabricated light filter.
Turning now to Figure 7 combinations 25 and 26 of the layers 2 through 5 and 2', 3', 4', 5' are arranged successively in the direction of the radia-tion 17 (~igure 2). The pro~osed light filter has two ~lass bases 27 (Yigure 7) and 2~.
_ 16 Referring to ~igure 8 combinations 29, 30 and 31 are spatially separated along the layer structu-re 1 made up of separate sections. Spatially separat-ed are, accordingly, radiations 32, 33 and 3~ at respective wavelengths ~ 2 and J 3 filtering by each combination 29 through 31, said radiations bein~ derived due to the effect cf the incident radiation on each secti~n of the structure l.
In ~igure 9 combinations 29', 30' and 31' of said layers are spatially aligned. Spatially aligned will be also radiations at respective wavelengths ~ 2 and /~3 after filtering by said combi-nations.
~igure 10 shows diagramatically another embodi-ment of the light filter whose production involves exposure of said element to a continuous radiatlon spectrum. In a layer structure 35, layers 2", 3", ~"
and 5" are arranged equidistantly in a cross-section formed by a plane 36 perpendicular to one of the layers 2" through 5" and to the direction, in which the thickness of the layers 2" through 5" changes.
The thicXness of the layers 2" through 5" changes in a monotone marner alon~ the layer structure 35. Such a filter permits obtaining the a~alyzed radiation sEectrum and continuously adjusting the wavelength of the filtered radiation 17 (~i~ure 2~ by Moving it in 2~ 8 front of a slit diaphragm (not shown in the draw-ing).
In another embodiment of the invention the light filter having essentially the same capabilities comp-rises the layer structure 1 (Figure 11) with a means37 for compressing said layer structure. Said compres-sing means includes a cramp 38 and a screw 39 changing the compressive force of the cramp 38. The layer structure 1 is made of an elastic compressive mate-rial, say bichromized gelatin.
After the layer structure 1 is compressed, itslayers 2" through 5" are equidistant (~igure 12) only in a cross-section, similarly to the embodiment of ~igure 10.
In compliance with the invention the section of the prism may represent a rhomboid 40 (~igure 13) or anisosceles triangle 41 (~igure 14), which is a par-ticular case of the rhomboid and is notj therefore, considered. Two symmetrical side faces 42 (~igure 13) and 43 of the rhomboid 40 accommodate two layer structures 1 and ~4. The luminous radiation 17 is directed to a free face 45, while the filtered ra-diation 19 reflected successively from the layer structures 1 and 44 comes out of another free face 46. An angle ~ between the free faces 45 and 46 is chosen as follows:
_ 18 = 2~ if ~ ~ 90~
Background Art There are known interference light filters comp-rising two or more groups of alternating layers of di-electric material with different refractive index, which have an optical thickness equal to a quarter wave of luminous flux directed to said light filter (cf. SU, A, 539,284; SU, A, 881,647).
Production of such filters generally involves un-wanted complexities. Moreover, the necessary protective coatings further complicate the manufacturing pro-cess and impair optical properties of said filters, that is, transmission of radiation.
Also, chemically pure materials may be required in production of the afore-mentioned filtersO
In the known light filters a wavelength may be continuously changed only within narrow limits.
~here are also known selective interference light filters having a layer structure wherein each layer reflects lurninous flow directed to said light 2~ 3s filter. The layer structure is formed with a dielect-ric layer deposited on a metal base and having a phase hal~-width multiple of ~ and with an even number of alternating quarter-wave layers of two dielectric 5 materials with high and low refractive index. Such a combination of layers is topped with an absorbing metal film whose thickness is much smaller than the operating wavelength (cf. Optika i spec~roskopiya, Volume ~0, 1976, Nauka publishers, ~eningrad, Goldina N,D. and ~roitsky J~.~., pp 935 - 938~.
Such a light filter reflects not only the select-ed wavelength but also other wavelengths beyond the reflection band, which are treated as interference.
Moreover, said light filters have essentially the same disadvantages as the light filters discussed pre-viously.
Briei De~cription of the I~vention It is an object of the present invention tocreate ~ selective interference light filter which would make it possible to continuously adjust, within wide limits, the operating wavelength in the event of variations of the angle of incidence of luminous flux.
Another object of the invention is to provide essentially without change, as compared with the prior art, the lightfilter spectral bandwidth, reflec-tion factor and contrast.
2 ~ 8 S
Still another object of the invention is to de-crease incident radiation background.
Yet another object of the invention is to increase further the continuous adjustment range.
A further object of the invention is to orovide a light filter capable of identifying a radiation spec-trum of various substances.
One more object of the invention is to create a light filter separating several spectral bands with dif-10 ferent wavelengths at the same time.
There is provided a selective interference light filter having a layer structure wherein each layer reflects luminous radiation direc'ed to the light fillter, in which, according to the invention, the 15 layers comprised in the layer structure are equidis-tant with the refractive index varyinp~ periodically in depth and are formed by exposing to at least one mono-chromatic radiation at a predetermined wavelength an element made of a light-sensitive material transpa-20 rent to said radiation and placed in front of a mirroronly during the emission of radiation.
As distinct from the known interference light filters formed by vacuum deposition of plane-parallel layers of pure materials, the proposed light filter 25 allows continuous adjustment of the operating wave-length within fairly wide limits.
The layer structure reflects different wavelengths, s depending on the angle of incidence of light directed to said structure.
The adjustment range of a wavelength reflected from the layer structure depends on effective refrac-tive index of said structure. More specifically, thegreater is the refractive index, the narrower is the adjustment range. On the other hand, the greater the number of layers forming the structure and the greater the dif~erence between their refractive indexes, the higher i9 the refractive index and the narrower is the spectral band.
The irradiated element may be fabricated from photoemulsion based on salts of silver or bichromized gelatin or a photorecording polymeric medium or a photopolymerizing composition of materials.
~ ormed by vacuum deposition are normally not more than 30 to 40 layers. A further increase in the number of layers re~ults in more defects. ~herefore,the reflection factor will not be increased and the spect-ral band will not be narrower. To obtain agreat ref-lection factor and a narrow spectral band with a small number of layers, use should be made of materials characterized by a great difference between refractive indexeq n1 and n2. Since n1 may not be less than 1.3, n2 normally exceeds 2. As a result, the effective refractive index is about 2 or greater.
A method of manufacturing the proposed light s filterJ permits obtaining light filters with a greater number of layers, more specifically, with some 100 to 200 layers, the thickness thereof (equal to half a waveleneth) being provided automatically to a desired accuracy, The effective refractive index of the layer system remains close to the refractive index of the source light-sensitive material (about 1.5 in the case of photoemulsion based on salts of silver~. A greater number of layers ensures, at a low modulation level of the refractive index, a high reflection factor and a narrow spectral band (essentially similar to that of filters made by deposition), whereas a low effec-tive refractive index provides for a wide wavelength adjustment range.
It is preferable that the light filter accord-ing to the invention should comprise a base accommo-dating a layer structure. The light filter with a base accommodating a layer structure has the following advantages over the known light filter without a base:
greater strength due to the base strength, a higher reflection factor, a narrower spectral band and better contrast due to exclusion from interference of a beam reflected from the air-layer structure interface. Depending on the material of the base and the operating wavelength range, the base may be used to suppress interlerence pec~ks of orders higher than the first working order of interference.
~r~ 85 The base may comprise at least one prism with a layer structure disposed on its reflecting face and luminous radiation directed to any free face thereof. Also, the base may represent at least one op-5 tical wedge with a layer structure arranged on its oneface and luminous radiation directed to the other face thereof. In another embodiment of the invention the base may be an element in the form of a lens.
The light filter comprising a base in the form 10 of a prism increases the operating wavelength adjust-ment range.
An advantage of the light filter having a base formed with an optical filter over the light filter having a flat base is that the beam reflected from the 15 air-base interface is separated from interfering beams linearly and, in addition, has another direction, as in the ca~e of a base in the form of a prism. On the other hand, the light filter cDmprising a wedge has the 3ame advantage as the light filter having a flat 20 b~se, more specifically, smaller d~nensions and corres-pondence of inpu~ and output faces.
The light filter comprising a base in the fo~n of a lens acts both as an optical filter element and a focusing ele~ent.
When an element of a light-sensitive material is e~po~ d to two or more monochromatic radiations with different wavelengths, the layer structure may have, 2~
respectively, two or more combinations of equidistant layers, each of which corresponds to the natural wave-length of said monochromatic radiation.
Such a light filter is polychromatic. It reflects simultaneously two or more wavelengths, each of which is readjusted after a change in the angle of incidence of radiation affecting said light filter.
It is of advantage that combinations of equidis-tant layers in the layer structure should be arranged successively along luminous radiation directed to said layer structure. It is also advantageous that said layers should be spatially aligned.
Production of the proposed light filter is sub-stantially simplified as compared with the prior art light filter. Spatial alignment of combinations of equidistant layers makes it possible to obtain to a higher accuracy the relation between Preset wavelengths upon reflection since different combinations of layers are formed simultaneously.
It is also advantageous that two or more combina-tions of equidistant layers should be formed by paral-lel beams of monochromatic radiation, while the layer structure contains separate sections comprising combi-nations of equidistant layers corresponding to sepa-rate sections of the wave front of luminous radiation directed to said layer structure.
Spatially separated beams of different wavelengths 2~ s are produced by such a light filter upon reflection.
It i~ further advantageous that the layer struc-ture should comprise layers made equidistant in a cross-section of said layer structure in a plane 5 which is, at the same time, perpendicular to any layer and to the thickness variation direction thereof and is formed by radiation characterized by a continuous spectrum.
Such a light filter makes it possible to adjust the wavelength both by changing the angle of incidence of light directed to the light filter and by displacing said light filter linearly in the vicinity of a slit diaphragm. The proposed light filter is characterized by fairly simple production techniques, which is an apparent advantage over the known wedge light filter made by wedge vacuum deposition of layers of material.
The layer structure may include a compression means providing for a linear change in the thickness of equidistant layers along said layer structure.
Therefore, in production of the light filter provision is made for changing the refractive index by fairly simple means.
The prism may have a rhomboidal section with identical layer structures being disposed on its two symmetrical side faces.
The prism may also have two pairs of syrnmetrical side faces with a common symmetry ~lane. Each side 2~ s face of one paix may accommodate layer structures.
Such a light filter is selective, as regards the wavelength and the angle of incidence. It ref-lects luminous radiation at only one wavelength in a predetermined direction. Moreover, said light filter may have smaller dimensions and reduced w~ht due to omission of inoperative parts of the rhomboid.
To provide for accurate setting of a filtered wavelength and monitoring of the angle of incidence Of light directed to the layer structure, it is ad-visable that the light filter according to the inven-tion should comprise a case whose walls are provided with two holes adapted, respectively, to pass radia-tion to the layer structure and to release the filter-ed radiation.
The layer structure may be installed in thecase in a manner allowing its turn and/or linear displacement relative to the emitted radiation.
~ Vith such an arrangement, the outgoing filter-ed radiation is not restricted to said hole in thecase, a feature being of appreciable importance in embodiments of the light filter characterized by spatial displacement of filtered radiation.
~urthermore, the light filter forming the sub-ject of the present invention may comprise a case,one wall of which is formed by an input face of the prism or optical wedge, while the opposite wall of s said case accommodates a diaphragm suited to pass radiation to the layer structure, the layer structure and the diaphragm being disposed in a manner allowing relative turn and/or linear displacement.
Such filters permit scanning and/or directing the beRm and/or adjusting the reflected wavelength.
The proposed light filter ensures continuous variation of the operating wavelength and is charac-terized by a narrow spectral band, high contrast and high reflection factor.
Brief Description o$ the Drawings Other object~ and features of the invention will become apparent from the description of preferred embodiment thereof, taken in col~junction with the ac-companying drawings, wherein:
~ igure 1 shows a selective interference lightfilter according to the invention;
~ igure 2 showæ the same light filter comprising a base in the form of a prism according to the inven~
tion;
~ igure 3 shows the same light filter comprising a base in the form of an optical wedge according to the invention;
~ 'igure 4 shows the same light filter comprising a base in the form of a lens according to the in-vention;
~igure 5 depicts a light filter incorporating 2 ~ 8 S
several prisms according to the invention;
~ igure 6 depicts a light filter comprising several optical wedges according to the invention;
Figure 7 shows a light filter with combinations of layers disposed successively in the direction of radiation according to the invention;
~ igure 8 shows a light filter with spatially separated combinations of layers according to the invention;
~igure 9 shows a light filter with spatially aligned combinations of layers according to the invention;
~ igure 10 shows a light filter enabling conti-nuou~ adjustment of a filtered radiation wavelength according to the invention;
~ igure 11 depicts a light filter comprising means for compressing a layer structure according to the invention;
71'igure 12 shows the same light filter with comp-ressed layers according to the invention;
~ igure 13 shows a light filter with a basehaving a rhomboida]. section according to the inven-tion;
~ i~ure 1~ shows a light filter comprising a base whose section represents an isosceles triangle according to the invention;
~igure 15 sh~ws a light filter with an intrica-_ 12 X~ 'lB5 tely shaped base according to the invention;
Figure 16 shows a light filter comprising acase according to the invention; and Figure 17 shows another embodiment of the light filter comprising a case according to the invention.
Detailed Description of the Invention Referring to the drawings the selective inter-ference light filter forming the subject of the pre-sent invention comprises a layer structure 1 (Figure 1) made up of equidistant layers 2, 3, ~ and 5 with re-fractive index periodically varying in depth. Produc-tion of such a light filter-is diagrammatically illu~qt-rated in ~igure 1. A parallel lu~inous flux G is directed to an element of a suitable transparent ligh~
-sensitive material through an optical system 7, said flux comin~ from a light source 8. ~uring the emission of radiation, the irradiated element is Dlaced in front of a metallic mirror 9 which is removed on comDletion of the radiation process. Said element is exposed to at least one monochromatic radiation at a predetermined wavelength ~ , The wave of the luminuous flux 6 reflected from the mirror 9 interferes with the incident wave whereby standing waves are formed. The refractive index of the light-sensitive material changes differently at crests 10 and nodal points 11 of the standing waves.
After ex~osure to radiation, said element of 2~ 5 li~ht-sensitive material acquires the layer structu-re 1. The crests 10 of said waves located equidistant-ly in the irradiated element at a distance ~0~2n from one another (where n is the re~ractive index of the material) correspond to the equidistant layers 2 through 5 in the layer structure 1. So, the perio-dicity of the layers 2 through 5 and, consequently, the layer thickness d = ~ (1). Vertical lines 2n mark schematically a plane 12, in which variations of the refractive index of the light-sensitive mate-rial are maximal, The number N of the layers 2 through 5 in the layer structure 1 depends on thick-ness D of the irradiated element and on thickness d of each layer 2 through 5 and is defined by the equation D D-2n N = - Jlc (2~
Each layer 2 through 5 partially reflects lumi-nous radiation directed to the layer structure. In-terference of the beams reflected from the layers 2 throug~ 5 is maximal at a predermined wavelength equal to the dif~erence between lengths of interfer-ing beams, Radiation at said wavelength is filtered by the proposed light filter upon reflection.
The irradiated element is made of a suitable transparent light-sensitive material which may be Z ~ 5 photoemulsion based on salts of silver or bichromi-zed gelatin or a photorecording polymeric medium or a photopolymerizing composition of materials, The layer structure 1 comprises a base formed with a prism 13 (~igure 2~ or an optical wedge 14 (~igure 3) or a lens 15 (~igure 4~.
In the prism 13 (~'igure 2~, the layer structure 1 is disposed on a reflective face 16, while luminous radiation 17 is directed to any free face 18. ~iltered 10 radiation 19 comes out through another face 20 of the prism 13.
Similarly, the layer structure 1 is arranged on a face 21 (~igure 3) of the optical ~edge 14, the luminous radiation 17 is directed to its face 22, and 15 the filtered radiation 19 comes out through the same face 22.
When use is made of the lens 15 (~igure 4), the light filter is designed in a manner similar to that described above, It doe~ not only filter the radiation 20 17 but also brings it into a focus 23 of the lens 15 if the luminuous radiation 17 is collimated.
In all the embodiments described, radiation 24 (~igures 2 through 4~ reflected from the environ-ment-light filter interface has a direction diffe-25 rent from that of the filtered radiation 19.
The base may comprise more than one prism 13 orwedge 14, as illustrated in ~igures 5 and 6. Prisms ;~G~ ~8' 13' (and wedges 14'~ are arranged along the structu-re 1 and their number depends on the length of the structure 1. Each prism 13' has dimensions and, consequently, weight much smaller than those in the embodiment of ~igure 2, wherein only one prism 13 is utilized. The weight and dimensions of all the prisms 13' are smaller than the weight and dimensions of the prism 13.
Therefore, overall dimensions and total weight of the light filter of Figure 5 are substantially smaller than those in the embodiment of ~igure 2~ It may be asserted that the construction of the entire light filter is quasi-flat. The light filter is de-signed in much the same manner in another embodiment comprising a plurality of wedges 14' t~igure 6).
The irradiated element may be exposed to two or more radiations at different wavelengths. Combi.na-tions of equidistant layers corres~onding to said wavelengths are formed in the element. Said combina-tions of layers in the layer structure may be ar-ranged differently to suit particular functions and applications of the fabricated light filter.
Turning now to Figure 7 combinations 25 and 26 of the layers 2 through 5 and 2', 3', 4', 5' are arranged successively in the direction of the radia-tion 17 (~igure 2). The pro~osed light filter has two ~lass bases 27 (Yigure 7) and 2~.
_ 16 Referring to ~igure 8 combinations 29, 30 and 31 are spatially separated along the layer structu-re 1 made up of separate sections. Spatially separat-ed are, accordingly, radiations 32, 33 and 3~ at respective wavelengths ~ 2 and J 3 filtering by each combination 29 through 31, said radiations bein~ derived due to the effect cf the incident radiation on each secti~n of the structure l.
In ~igure 9 combinations 29', 30' and 31' of said layers are spatially aligned. Spatially aligned will be also radiations at respective wavelengths ~ 2 and /~3 after filtering by said combi-nations.
~igure 10 shows diagramatically another embodi-ment of the light filter whose production involves exposure of said element to a continuous radiatlon spectrum. In a layer structure 35, layers 2", 3", ~"
and 5" are arranged equidistantly in a cross-section formed by a plane 36 perpendicular to one of the layers 2" through 5" and to the direction, in which the thickness of the layers 2" through 5" changes.
The thicXness of the layers 2" through 5" changes in a monotone marner alon~ the layer structure 35. Such a filter permits obtaining the a~alyzed radiation sEectrum and continuously adjusting the wavelength of the filtered radiation 17 (~i~ure 2~ by Moving it in 2~ 8 front of a slit diaphragm (not shown in the draw-ing).
In another embodiment of the invention the light filter having essentially the same capabilities comp-rises the layer structure 1 (Figure 11) with a means37 for compressing said layer structure. Said compres-sing means includes a cramp 38 and a screw 39 changing the compressive force of the cramp 38. The layer structure 1 is made of an elastic compressive mate-rial, say bichromized gelatin.
After the layer structure 1 is compressed, itslayers 2" through 5" are equidistant (~igure 12) only in a cross-section, similarly to the embodiment of ~igure 10.
In compliance with the invention the section of the prism may represent a rhomboid 40 (~igure 13) or anisosceles triangle 41 (~igure 14), which is a par-ticular case of the rhomboid and is notj therefore, considered. Two symmetrical side faces 42 (~igure 13) and 43 of the rhomboid 40 accommodate two layer structures 1 and ~4. The luminous radiation 17 is directed to a free face 45, while the filtered ra-diation 19 reflected successively from the layer structures 1 and 44 comes out of another free face 46. An angle ~ between the free faces 45 and 46 is chosen as follows:
_ 18 = 2~ if ~ ~ 90~
(3) ~ = 360 - 2~ if ~ ~90 where ~ is the angle between the faces 42 and 43 accommodating the layer structures 1 and 44, respec-tively.
In a general case a prism 47 (~igure 15) i9 intri-cately shaped and comprises at least two pairs of respectively symmetrical side faces 48, 49 and 50, 51 with a common symmetr~ p~ane. One pair of said faces 48, 49 accommodates the layer structures 1, 44, and the angles ~ and ~ between said pairs of the faces 48, 49 and 50, 51, respectively, are chosen by refe-rence to equation (3). The luminous radiation 17 coming to the free face 50 is successively reflected from the layer structures 44 and 1. The filtered ra-diation 19 comes out of the free face 51.
Turning now to ~igure 16 the illustrated light filter comprising the layer structure 1 disposed on the prism 13 has a case 52 having an input hole 53 to pass the radiation 17 and a hole 54 al]o~ing exit of the filtered radiation 19. The input hole 53 in conjunction with holes 55 and 56 forms a di&phragm which may be, for example,any light guide.
The layer structure 1 is arranged relative to the emitted radiation 17 so tlat it may turn with respect to the case 52 and also move linearly inde-2~ 5 pendently or simultaneously. ~o accomplish this, the prism 13 accommodating the layer structure includes a turning mechanism comprising, for example, a worm--and-worm gear 57, 58 and a handle 59. The prism 13 5 is secured to the gear 57 of the worm set 57, 58. More-over, the prism is linearly displaced by a screw 60 interacting with the gear 57 loaded with a spring 61.
The radiation 17 is transmitted through said diaphragm formed by the holes 5~, 55, 56 to the prism 10 whereupon the filtered radiation comes out of the hole 54 on the opposite wall of the case 52.
The case 52' (~igure 17~ may be located beyond the light filter, one of its walls serving as the input face 16 of the prism 13. Arranged on the opposi-15 te wall of the case 52' is the diaphragm formed bythe system comprising the holes 53, 55 and 56 in a sleeve 63. ~he mechanism enabling linear displace-ment of the prism 13 comprises a screw 64 and a spring 65, which interact with the sleeve 63 of the diaphragm 20 to provide for relative linear displacement of the diaphragm and the prism 13. This is done to change the angle of incidence of the radiation 17 directed to the layer structure 1. The prism 13 secured to a rotary base 66 is turned by changing the shape of the 25 case 52' representing bellows. The filtered radiation 19 comes out of the light filter through the face 20.
The selective interference light filter forming 2~ ~8 ~ S
the subject of the present invention operates in the following manner.
The luminuous radiation 17 is directed to the light filter and each layer 2 through 5 (Figure 2) 5 comprised in the layer structure 1 reflects a small portion of said radiation. The reflected radiation 19 consists of a multitude of light beams characteriz-ed by a constant difference in length, which depends on the layer thickness d, the refractive index n and the angle of incidence ~C of light directed to the layer structure 1. The result of interference is such that its peak is attainable only for the wave-length ~ satisfying the following condition:
A = 2dn cos~C (4) The wavelength of the reflected radiation 1 m~y be varied by changing the angle of incidence /~
of light directed to the light filter.
The light-sensitive material of the irradiated element is chosen to be practically transparent to radiation at the predetermined wavelength ~1O. The refractive index of said material may vary slightly under the action of light and its resolution should be sufficient to provide for formation of a layer structure (internal homogeneities within the material should be smaller than /l/15).
In the light filter comprising a base, the ra-diation 21 reflected from the air-filter interface is linearly separated from the radiation 19 reflected from the layers 2 through 5 or even has another direc-tion. Hence, it does not interfere with the radiation19. Consequently, the interference pattern will not be impaired.
If the base i9 a prism or an optical wedge, the radiation 24 reflected from the air-filter interface 10 is separated angularly and the wavelength adjustment range is wider than in the case of a plane-parallel base.
When the lens 15 (~igure 4) is u~ed, the reflect-ed radiation 19 has a peak at one wavelength, mono-15 chromatic light being focused at the focal point23 of the lens 15 if a plane-parallel light beam is incident on the light filter.
When the radiation 17 characterized by a conti-nuous spectrum is incident on the light filter compris-20 ing the combinations 25, 26, 29, 30 and 31 of saidlayers, it reflects two or more wavelengths. The wave~
may be spatially aligned (29', 30', 31'~ or separat-ed (29, 30, 31).
When the radiation 17 is incident on different 25 sections of the light filter of ~igure 8 with layers var~ing in thickness, different wavelengths ~ 1 /~ 2~ ~l3 are reflected.
The wavelength /1 of reflected light changes z~ s as the light filter and the incident beam of lumi-nous radiation are displaced relative to each other over a distance x without varying the angle of in-cidence of the radiation directed to said light filter.
It is also possible to change the wavelength of reflec-ted light by varying the angle of incidence of light directed to said light filter. The light filter illust-rated in ~igures 11 and 12 permits changing the value d/l/dx, that is, di~persion thereof.
If the light filter o~ Figures 13 and 13 is affec-ted by luminous radiation characterized by any spect-rum and transmitted at any angle, said light filter will reflect only one wavelength solely in case when said wave affects the light filter at a predetermined angle (parameters of the prism are chosen so as to provide for separation of the radiation incident on the light filter at right angles to the input face 31)~
The light filter of Figures 15, 16 and 17 gives off solely the light incident thereon at right angleq since the diaphragm (~`igures 16 and 17) does not pass oblique beams. The light filter filters the light at only one wavelength with the diaphragm and the layer structure 1 relatively disposed in a prede~
termined manner. The light filter may be tuned to any 25 wavelength within a preset range by changing relati~e position of said diaphragm and the layer structure 1.
~he orientation of the light filter is changed to effect angle scanning, that is, to determine the direction to the source of light (not shown in the drawing) at a predetermined wavelength.
Given below are examples illustrating the use of the preferred embodiments of the light filter.
Example 1 The selective interference light filter has a layer structure of photoemulsion containing silver bromide. The layer structure is 18 ~ thick. It con-sists of at least 85 layers. The refractive index va-ries from 1.52 to 1,60. Said layer structure is form-ed by light emitted by a helium-neon (~e-Ne) laser at the wavelength /~0 = 633 nm. The filtered radiation has the wavelength A in the range from 480 to 633 nm.
The reflection factor is up to 40~o in the green spectrum. The spectral bandwidth is within 8 - 10 nm within the entire wavelength adjustment range.
Example 2 The selective interference light filter compris-es a layer structure of bromated gelatin (with ammo-nium bichromate). The layer structure is 10 ~ thick.
It consists of at least 60 layers. The re~ractive index varies from 1.50 to 1.60. Said layer structure is formed by light from an argon (Ar+) laser at the wavelength /lo = 488 nm. The filtered radiation has a wavelength in the range from 380 to 488 nm. The - 2~ -X ~ 85 reflection factor i9 Up to 70~o in the blue and greenregions of the spectrum. The spectral bandwidth is within 5 - 6 nm.
xample 3 The selective interference light filter compris-es a layer structure of a photorecording polymeric medium representing an oxidizable recording medium with anthracene. The layer structure is 1 mm thick.
It consists of at least 4500 layers. Said layer struc-10 ture is formed by light from a helium-neon (He-Ne) laser at the wavelength A 0 = 633 nm. The filtered radiation has a wavelength in the range from 475 to 633 nm. The reflection factor is up to 10% in the green spectrum. The spectral bandwidth is within 0.1 - 0.2 nm.
ExamPle 4 The selective interference light filter comp-rises a layer structure of a liquid polymerizing compound. The compound contains a radically polyme-rized vinyl monomer and a stabilizing additive. ~he layer structure is 20JU thick. Said layer structure is formed by light from a helium-cadmium (~e-Cd) laser at the wavelength /lo = 442 nm and consists of about 130 layers. The filtered radiation has a wavelength from 350 to 442 ~m. The reflection factor is 15~ ~nd the spectral bandwidth is within 3 - 4 nm.
Z~8i~5 Exam~le 5 The selective interference light filter comp-rises a layer structure of photoemulsion containing silver bromide. The layer 3tructure is 21JU thick. It consists of at least 100 layers. Said layer structure is formed by light from a helium-neon (He-Ne~ laser at the wavelength /~O = 633 nm. Said layer structure is dispo~ed on the ~o~nu~e fa~e of a triang~r p~sm with a~ ~ 90 45 and 45 . The filtered radiation has a wavelength 10 in the range from 360 to 610 nm. The reflection factor iq 40% or more in the red and violet qpectra and up to 70% in the green spectrum. The spectral bandwidth is within 8 - 10 nm.
Example 6 The ~elective interference light filter comprises a layer structure of photoemulsion containing silver bromide. The layer structure is 21)u thick. It con-sists of at least 100 layers. Said layer structure is formed by light from a helium-neon (Ne--Ne) laser at the wavelength ~0 = 633 nm. Said layer ~qtructure i~
disposed on the face of an optical wedge with an angle of 30. The filtered radiation has a wavelength in the range from 570 to 633 nm. The reflection factor is about 60~.
Example 7 The selective interference light filter comprises ~ 85 a layer structure of photoemulsion containing silver bromide. The layer structure is 21JU thick. Said lay-er structure is formed by light from a helium-neon (,~e-Ne) laser at the wavelength i~ 01 = 633 nm in 5 one part of the photoemulsion plate and by light from an argon (Ar+~ laser at the wavelength ~02 = 488 nm in the other part of said photoemulsion plate.
The layer structure is disposed on a flat base.
The filtered radiation has two wave~ hs in a beam of adjacent waves. If a screen is placed in the way of said filtered radiation, the spot on the screen will comprise two parts of different colours. As the ; angle of incidence of luminous radiation directed to the light filter varies from 0 to +35, both wave-lengths will change. More specifically, the shorter wavelength will change from 380 to 488 nm and the longer wavelength from 570 to 633 nm.
Exam~le 8 The selective interference light filter com~ris-es a layer structure of photoemulsion containing sil-ver bromide. The layer structure is 42 ~ thick. Said layer structure is formed by radiation emitted by two lasers having the wavelengths ~lo = 633 nm and Ro = 488 nm. The layers formed by the first laser occupy the first half of the plate in thickness. Con-versely, the layers formed by the second laser occupy the second part of the plate in thickness. The first 2~
combination of layers is disposed ahead of the second combination of layers in the way of radiation inci-dent on said light filter. An analysis of the filtered radiation sho~rs that it has two wavelengths at one angle of incidence on said light filter. As the angle of incidence changes, the filtered radiation wave-lengths vary from 570 to 633 nm and from 350 to 488 nm for /lo and /10, respectively.
Example 9 The selective interference light filter comprises a layer structure of photoemulsion containing silver bromide. The layer structure is formed by radiation at the wavelength /lo = 633 nm and is disposed on both legs of a triangular prisnl with angles 90, 45 and 45, said prism being a particular case of a rhomboid. The light filter is exposed to radiation from a source characterized by a continuous spectrum. The filtered radiation has a wavelength of 449 nm and a s~ectral bandwidth of 10 nm. The filtration occurs only when the radiation is normal to said light filter, As the angle of incidence changes by 1, the intensity of the filtered radiation decreases twice. The light filter does not practically pass luminous radiation when the angle of incidence changes by 2.
The proposed light filter is a selective narrow-band filter adjustable in wavelengt'ns. Its production is substantially simplified and the range of its uses ~ 8 5 i9 increased, which is an apparent advantage over the prior art.
~ he adjustable light filter having an adjust-ment range within 240 nm at a ~pectral bandwidth of 8 nm can replace 30 unadjustable light filters having the same spectral bandwidth. Considering the cost of one light filter the invention can be very effective economically,
In a general case a prism 47 (~igure 15) i9 intri-cately shaped and comprises at least two pairs of respectively symmetrical side faces 48, 49 and 50, 51 with a common symmetr~ p~ane. One pair of said faces 48, 49 accommodates the layer structures 1, 44, and the angles ~ and ~ between said pairs of the faces 48, 49 and 50, 51, respectively, are chosen by refe-rence to equation (3). The luminous radiation 17 coming to the free face 50 is successively reflected from the layer structures 44 and 1. The filtered ra-diation 19 comes out of the free face 51.
Turning now to ~igure 16 the illustrated light filter comprising the layer structure 1 disposed on the prism 13 has a case 52 having an input hole 53 to pass the radiation 17 and a hole 54 al]o~ing exit of the filtered radiation 19. The input hole 53 in conjunction with holes 55 and 56 forms a di&phragm which may be, for example,any light guide.
The layer structure 1 is arranged relative to the emitted radiation 17 so tlat it may turn with respect to the case 52 and also move linearly inde-2~ 5 pendently or simultaneously. ~o accomplish this, the prism 13 accommodating the layer structure includes a turning mechanism comprising, for example, a worm--and-worm gear 57, 58 and a handle 59. The prism 13 5 is secured to the gear 57 of the worm set 57, 58. More-over, the prism is linearly displaced by a screw 60 interacting with the gear 57 loaded with a spring 61.
The radiation 17 is transmitted through said diaphragm formed by the holes 5~, 55, 56 to the prism 10 whereupon the filtered radiation comes out of the hole 54 on the opposite wall of the case 52.
The case 52' (~igure 17~ may be located beyond the light filter, one of its walls serving as the input face 16 of the prism 13. Arranged on the opposi-15 te wall of the case 52' is the diaphragm formed bythe system comprising the holes 53, 55 and 56 in a sleeve 63. ~he mechanism enabling linear displace-ment of the prism 13 comprises a screw 64 and a spring 65, which interact with the sleeve 63 of the diaphragm 20 to provide for relative linear displacement of the diaphragm and the prism 13. This is done to change the angle of incidence of the radiation 17 directed to the layer structure 1. The prism 13 secured to a rotary base 66 is turned by changing the shape of the 25 case 52' representing bellows. The filtered radiation 19 comes out of the light filter through the face 20.
The selective interference light filter forming 2~ ~8 ~ S
the subject of the present invention operates in the following manner.
The luminuous radiation 17 is directed to the light filter and each layer 2 through 5 (Figure 2) 5 comprised in the layer structure 1 reflects a small portion of said radiation. The reflected radiation 19 consists of a multitude of light beams characteriz-ed by a constant difference in length, which depends on the layer thickness d, the refractive index n and the angle of incidence ~C of light directed to the layer structure 1. The result of interference is such that its peak is attainable only for the wave-length ~ satisfying the following condition:
A = 2dn cos~C (4) The wavelength of the reflected radiation 1 m~y be varied by changing the angle of incidence /~
of light directed to the light filter.
The light-sensitive material of the irradiated element is chosen to be practically transparent to radiation at the predetermined wavelength ~1O. The refractive index of said material may vary slightly under the action of light and its resolution should be sufficient to provide for formation of a layer structure (internal homogeneities within the material should be smaller than /l/15).
In the light filter comprising a base, the ra-diation 21 reflected from the air-filter interface is linearly separated from the radiation 19 reflected from the layers 2 through 5 or even has another direc-tion. Hence, it does not interfere with the radiation19. Consequently, the interference pattern will not be impaired.
If the base i9 a prism or an optical wedge, the radiation 24 reflected from the air-filter interface 10 is separated angularly and the wavelength adjustment range is wider than in the case of a plane-parallel base.
When the lens 15 (~igure 4) is u~ed, the reflect-ed radiation 19 has a peak at one wavelength, mono-15 chromatic light being focused at the focal point23 of the lens 15 if a plane-parallel light beam is incident on the light filter.
When the radiation 17 characterized by a conti-nuous spectrum is incident on the light filter compris-20 ing the combinations 25, 26, 29, 30 and 31 of saidlayers, it reflects two or more wavelengths. The wave~
may be spatially aligned (29', 30', 31'~ or separat-ed (29, 30, 31).
When the radiation 17 is incident on different 25 sections of the light filter of ~igure 8 with layers var~ing in thickness, different wavelengths ~ 1 /~ 2~ ~l3 are reflected.
The wavelength /1 of reflected light changes z~ s as the light filter and the incident beam of lumi-nous radiation are displaced relative to each other over a distance x without varying the angle of in-cidence of the radiation directed to said light filter.
It is also possible to change the wavelength of reflec-ted light by varying the angle of incidence of light directed to said light filter. The light filter illust-rated in ~igures 11 and 12 permits changing the value d/l/dx, that is, di~persion thereof.
If the light filter o~ Figures 13 and 13 is affec-ted by luminous radiation characterized by any spect-rum and transmitted at any angle, said light filter will reflect only one wavelength solely in case when said wave affects the light filter at a predetermined angle (parameters of the prism are chosen so as to provide for separation of the radiation incident on the light filter at right angles to the input face 31)~
The light filter of Figures 15, 16 and 17 gives off solely the light incident thereon at right angleq since the diaphragm (~`igures 16 and 17) does not pass oblique beams. The light filter filters the light at only one wavelength with the diaphragm and the layer structure 1 relatively disposed in a prede~
termined manner. The light filter may be tuned to any 25 wavelength within a preset range by changing relati~e position of said diaphragm and the layer structure 1.
~he orientation of the light filter is changed to effect angle scanning, that is, to determine the direction to the source of light (not shown in the drawing) at a predetermined wavelength.
Given below are examples illustrating the use of the preferred embodiments of the light filter.
Example 1 The selective interference light filter has a layer structure of photoemulsion containing silver bromide. The layer structure is 18 ~ thick. It con-sists of at least 85 layers. The refractive index va-ries from 1.52 to 1,60. Said layer structure is form-ed by light emitted by a helium-neon (~e-Ne) laser at the wavelength /~0 = 633 nm. The filtered radiation has the wavelength A in the range from 480 to 633 nm.
The reflection factor is up to 40~o in the green spectrum. The spectral bandwidth is within 8 - 10 nm within the entire wavelength adjustment range.
Example 2 The selective interference light filter compris-es a layer structure of bromated gelatin (with ammo-nium bichromate). The layer structure is 10 ~ thick.
It consists of at least 60 layers. The re~ractive index varies from 1.50 to 1.60. Said layer structure is formed by light from an argon (Ar+) laser at the wavelength /lo = 488 nm. The filtered radiation has a wavelength in the range from 380 to 488 nm. The - 2~ -X ~ 85 reflection factor i9 Up to 70~o in the blue and greenregions of the spectrum. The spectral bandwidth is within 5 - 6 nm.
xample 3 The selective interference light filter compris-es a layer structure of a photorecording polymeric medium representing an oxidizable recording medium with anthracene. The layer structure is 1 mm thick.
It consists of at least 4500 layers. Said layer struc-10 ture is formed by light from a helium-neon (He-Ne) laser at the wavelength A 0 = 633 nm. The filtered radiation has a wavelength in the range from 475 to 633 nm. The reflection factor is up to 10% in the green spectrum. The spectral bandwidth is within 0.1 - 0.2 nm.
ExamPle 4 The selective interference light filter comp-rises a layer structure of a liquid polymerizing compound. The compound contains a radically polyme-rized vinyl monomer and a stabilizing additive. ~he layer structure is 20JU thick. Said layer structure is formed by light from a helium-cadmium (~e-Cd) laser at the wavelength /lo = 442 nm and consists of about 130 layers. The filtered radiation has a wavelength from 350 to 442 ~m. The reflection factor is 15~ ~nd the spectral bandwidth is within 3 - 4 nm.
Z~8i~5 Exam~le 5 The selective interference light filter comp-rises a layer structure of photoemulsion containing silver bromide. The layer 3tructure is 21JU thick. It consists of at least 100 layers. Said layer structure is formed by light from a helium-neon (He-Ne~ laser at the wavelength /~O = 633 nm. Said layer structure is dispo~ed on the ~o~nu~e fa~e of a triang~r p~sm with a~ ~ 90 45 and 45 . The filtered radiation has a wavelength 10 in the range from 360 to 610 nm. The reflection factor iq 40% or more in the red and violet qpectra and up to 70% in the green spectrum. The spectral bandwidth is within 8 - 10 nm.
Example 6 The ~elective interference light filter comprises a layer structure of photoemulsion containing silver bromide. The layer structure is 21)u thick. It con-sists of at least 100 layers. Said layer structure is formed by light from a helium-neon (Ne--Ne) laser at the wavelength ~0 = 633 nm. Said layer ~qtructure i~
disposed on the face of an optical wedge with an angle of 30. The filtered radiation has a wavelength in the range from 570 to 633 nm. The reflection factor is about 60~.
Example 7 The selective interference light filter comprises ~ 85 a layer structure of photoemulsion containing silver bromide. The layer structure is 21JU thick. Said lay-er structure is formed by light from a helium-neon (,~e-Ne) laser at the wavelength i~ 01 = 633 nm in 5 one part of the photoemulsion plate and by light from an argon (Ar+~ laser at the wavelength ~02 = 488 nm in the other part of said photoemulsion plate.
The layer structure is disposed on a flat base.
The filtered radiation has two wave~ hs in a beam of adjacent waves. If a screen is placed in the way of said filtered radiation, the spot on the screen will comprise two parts of different colours. As the ; angle of incidence of luminous radiation directed to the light filter varies from 0 to +35, both wave-lengths will change. More specifically, the shorter wavelength will change from 380 to 488 nm and the longer wavelength from 570 to 633 nm.
Exam~le 8 The selective interference light filter com~ris-es a layer structure of photoemulsion containing sil-ver bromide. The layer structure is 42 ~ thick. Said layer structure is formed by radiation emitted by two lasers having the wavelengths ~lo = 633 nm and Ro = 488 nm. The layers formed by the first laser occupy the first half of the plate in thickness. Con-versely, the layers formed by the second laser occupy the second part of the plate in thickness. The first 2~
combination of layers is disposed ahead of the second combination of layers in the way of radiation inci-dent on said light filter. An analysis of the filtered radiation sho~rs that it has two wavelengths at one angle of incidence on said light filter. As the angle of incidence changes, the filtered radiation wave-lengths vary from 570 to 633 nm and from 350 to 488 nm for /lo and /10, respectively.
Example 9 The selective interference light filter comprises a layer structure of photoemulsion containing silver bromide. The layer structure is formed by radiation at the wavelength /lo = 633 nm and is disposed on both legs of a triangular prisnl with angles 90, 45 and 45, said prism being a particular case of a rhomboid. The light filter is exposed to radiation from a source characterized by a continuous spectrum. The filtered radiation has a wavelength of 449 nm and a s~ectral bandwidth of 10 nm. The filtration occurs only when the radiation is normal to said light filter, As the angle of incidence changes by 1, the intensity of the filtered radiation decreases twice. The light filter does not practically pass luminous radiation when the angle of incidence changes by 2.
The proposed light filter is a selective narrow-band filter adjustable in wavelengt'ns. Its production is substantially simplified and the range of its uses ~ 8 5 i9 increased, which is an apparent advantage over the prior art.
~ he adjustable light filter having an adjust-ment range within 240 nm at a ~pectral bandwidth of 8 nm can replace 30 unadjustable light filters having the same spectral bandwidth. Considering the cost of one light filter the invention can be very effective economically,
Claims (32)
1. A selective interference light filter comp-rising a first layer structure having a plurality of layers forming a first combination of layers, each layer of said plurality of layers reflecting luminous radiation directed thereto; layers of said plurality made equidistant with refractive index varying perio-dically in depth; said first layer structure obtained by the use of an irradiated element made of a light--sensitive material and exposed to at least one mono-chromatic radiation at a predetermined wavelength;
said light-sensitive material transparent to said monochromatic radiation; said irradiated element placed in front of a mirror only during the emission of radiation and removed on completion of radiation of said irradiated element.
said light-sensitive material transparent to said monochromatic radiation; said irradiated element placed in front of a mirror only during the emission of radiation and removed on completion of radiation of said irradiated element.
2. A selective interference light filter as claimed in Claim 1, wherein said first layer structure is formed with said irradiated element made of a light-sensitive material chosen from the group comp-rising photoemulsion based on salts of silver, bi-chromized gelatin, a photorecording polymeric medium and a photopolymerizing composition of materials.
3. A selective interference light filter as claimed in Claim 1 or 2, comprising a base accommodat-ing said first layer structure.
4. A selective interference light filter as claimed in Claim 3, wherein said base is a prism having a reflective face accommodating said first layer structure and a free face exposed to lumi-nuous radiation.
5. A selective interference light filter as claimed in Claim 3, in which said base comprises a multitude of prisms disposed in close proximity to one another and combined by said first layer structure which is arranged on said multitude of prisms.
6. A selective interference light filter as claimed in Claim 3, wherein said base is an optical wedge having a first face accommodating said first layer structure and a second face exposed to luminous radiation.
7. A selective interference light filter as claimed in Claim 3, wherein said base is an element in the form of a lens.
8. A selective interference light filter as claimed in Claim 1 or 2, comprising said first layer structure having a plurality of combinations of equi-distant layers; each combination of said plurality of combinations corresponding to a natural wavelength of monochromatic radiation; said plurality of combi-nations formed by exposing said element of a light--sensitive material to a corresponding plurality of monochromatic radiations having different wavelengths.
9. A selective interference light filter as claim-ed in Claim 3, comprising said first layer structure having a plurality of combinations of equidistant lay-ers; each combination of said plurality of combinations corresponding to a natural wavelength of monochromatic radiation; said plurality of combinations formed by exposing said element of a light-sensitive material to a corresponding plurality of monochromatic radiations having different wavelengths.
10. A selective interference light filter as claimed in Claim 3, comprising a means for compress-ing said first layer structure, said means being dis-posed on said first layer structure and providing for a linear variation of thickness of said equidistant layers along said first layer structure.
11. A selective interference light filter as claimed in Claim 4, comprising said prism with a rhomboidal section, having first and second symmetri-cal side faces; a second layer structure similar to said first layer structure; said first and said second layer structures arranged, respectively, on said first and said second symmetrical side faces.
12. A selective interference light filter as claimed in Claim 4, comprising said prism having first and second symmetrical side faces and a common plane thereof, which forms a first pair of side faces;
third and fourth symmetrical side faces forming a second pair of side faces; a third layer structure similar to said first layer structure; said first layer structure and said third layer structure dis-posed, respectively, on said first side face and on said third side face.
third and fourth symmetrical side faces forming a second pair of side faces; a third layer structure similar to said first layer structure; said first layer structure and said third layer structure dis-posed, respectively, on said first side face and on said third side face.
13. A selective interference light filter as claimed in Claim 8, wherein in said first layer struc-ture said combinations of said plurality of combina-tions in conjunction with said first combination are arranged successively along luminous radiation direct-ed to said first layer structure.
14. A selective interference light filter as claimed in Claim 8, wherein in said first layer structure said combinations of said plurality of combinations in conjunction with said first combi-nation are arranged successively along lumious radia-tion directed to said first layer structure and are spatially aligned.
15. A selective interference light filter as claimed in Claim 8, in which said first layer struc-ture comprises sections corresponding to separate sections of a wave front of luminous radiation direct-ed to said first layer structure, said sections having their combination of equidistant layers and being formed with parallel beams of monochromatic radiation.
16. A selective interference light filter as claimed in Claim 8, wherein said plurality of layers of said first layer structure is arranged so that said layers are equidistant in a cross-section of said first layer structure in a plane perpendicular both to the direction, in which thickness of said plurality of layers changes, and to any layer of said plurality of layers; said plurality of layers formed with radiation characterized by a continuous spect-rum.
17. A selective interference light filter as claimed in Claim 9, wherein in said first layer structure said combinations of said plurality of combinations in conjunction with said first combina-tion are arranged successively along luminous radia-tion directed to said first layer structure.
18. A selective interference light filter as claimed in Claim 9, wherein in said first layer struc-ture said combinations of said plurality of combina-tions in conjunction with said first combination are arranged successively along luminous radiation direct-ed to said first layer structure and are spatially aligned.
19. A selective interference light filter as claimed in Claim 9, wherein said first layer struc-ture comprises sections corresponding to separate sections of a wave front of luminous radiation directed to said first layer structure, said sections having their combination of equidistant layers and being formed by parallel beams of monochromatic radia-tion,
20. A selective interference light filter as claimed in Claim 9, wherein said plurality of layers of said first layer structure is arranged so that said layers are equidistant in a cross-section of said first layer structure in a plane perpendicular both to the direction, in which thickness of said plurality of layers changes, and to any layer of said plurality of layers; said plurality of layers formed by radiation characterized by a continuous spectrum.
21. A selective interference light filter compris-ing: a first layer structure made up of a plurality of layers forming a first combination of layers; each layer of said plurality of layers reflecting luminous radiation directed thereto; layers of said plurality made equidistant with refractive index varying perio-dically in depth; said first layer structure formed with an irradiated element made of a light-sensitive material and exposed to at least one monochromatic radiation at a predetermined wavelength; said light-sensitive layer transparent to said monochromatic radi-ation; said irradiated element placed in front of a mirror only during the emission of radiation and re-moved on completion of radiation of said irradiated element; a case having a first wall and a second wall and accommodating said first layer structure; a first hole provided in said first wall of said case and adapted to pass luminous radiation to said first layer structure; a second hole provided in said second wall of said case and adapted to release radiation filtered by the entire light filter.
22. A selective interference light filter as claimed in Claim 21, wherein said first layer structu-re is turned and linearly displaced relative to the incoming radiation.
23. A selective interference light filter as claimed in Claim 21, wherein said first layer structu-re turns relative to the incoming radiation.
24. A selective interference light filter as claimed in Claim 21, wherein said first layer structu-re is linearly displaced relative to the incoming radiation.
25. A selective interference light filter as claimed in Claim 21 or 22 or 23 or 24, comprising a base which is a prism having a reflective face accommo-dating said first layer structure and a free face recei-ving luminous radiation; said first wall of said case formed with said free face of said prism; said second wall of said case being opposite to said first wall; a diaphragm disposed on said second wall of said case and suited to pass radiation to said first layer structure.
26. A selective interference light filter as claimed in Claim 21 or 22 or 23, or 24, comprising: a base formed with an optical wedge and having a first face accommodating said first layer structure and a second face receiving luminous radiation; said first wall of said case formed with said second face of said optical wedge; said second wall of said case being opposite to said first wall; a diaphragm dis-posed on said second wall of said case and suited to pass radiation to said first layer structure.
27. A selective interference light filter as claimed in Claim 25, wherein said first layer structu-re and said diaphragm relatively turn.
28. A selective interference light filter as claimed in Claim 25, wherein said first layer struc-ture and said diaphragm are linearly disposed relative to each other.
29. A selective interference light filter as claimed in Claim 25, wherein said first layer struc-ture and said diaphragm are relatively turned and linearly displaced with respect to each other.
30. A selective interference light filter as claimed in Claim 26, wherein said first layer structu-re and said diaphragm are relatively turned.
31. A selective interference light filter as claimed in Claim 26, wherein said first layer struc-ture and said diaphragm are linearly displace relative to each other.
32. A selective interference light filter as claimed in Claim 26, wherein said first layer structu-re and said diaphragm are relatively turned and li-nearly displaced with respect to each other.
- 38 .
- 38 .
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2008485 CA2008485A1 (en) | 1990-01-24 | 1990-01-24 | Selective interference light filter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2008485 CA2008485A1 (en) | 1990-01-24 | 1990-01-24 | Selective interference light filter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2008485A1 true CA2008485A1 (en) | 1991-07-24 |
Family
ID=4144116
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2008485 Abandoned CA2008485A1 (en) | 1990-01-24 | 1990-01-24 | Selective interference light filter |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2008485A1 (en) |
-
1990
- 1990-01-24 CA CA 2008485 patent/CA2008485A1/en not_active Abandoned
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