CN102707542B - Method for regulating best matching state of type-II KDP (Potassium Dihydrogen Phosphate) crystal for frequency multiplication of infrared light - Google Patents
Method for regulating best matching state of type-II KDP (Potassium Dihydrogen Phosphate) crystal for frequency multiplication of infrared light Download PDFInfo
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Abstract
The invention discloses a method for regulating best matching state of a type-II KDP crystal for frequency multiplication of infrared light. Adopted devices comprise a He-Ne light source, a pore aperture, a long-focus lens, a Rochon prism, a photoelectric probe and an oscilloscope. The method comprises the following steps of: firstly, roughly regulating a phase matching angle of the KDP crystal by using an auxiliary light source; secondly, focusing generated weak green lights on the Rochon prism via the long-focus lens, and regulating an azimuth angle of the KDP crystal according to the characteristics of the emergent light of the Rochon prism; and finally, regulating the phase matching angle of the KDP crystal by means of the photoelectric probe and the oscilloscope till the second frequency-multiplied output is the maximum. The method for regulating best matching state of the type-II KDP crystal for frequency multiplication of infrared light disclosed by the invention is characterized in that the azimuth angle of the KDP crystal is regulated by smartly utilizing the polarization detection characteristics of the Rochon prism and the KDP crystal is conveniently regulated in the weaker fundamental frequency light; the frequency multiplication efficiency of the KDP crystal is optimized and the polarization state of the frequency multiplication is guaranteed. The method for regulating best matching state of the type-II KDP crystal for frequency multiplication of infrared light disclosed by the invention has the characteristics of convenience in regulation, simpleness and high efficiency, and strong practicability.
Description
Technical field
The present invention relates to macro-energy double-frequency laser system, particularly the control method of a kind of II class KDP crystal to infrared light frequency multiplication optimum matching state.
Background technology
Ultrashort ultra-intense laser will provide new research means for the development in the fields such as the ultrafast science of high field, Relativistic Nonlinear physics, astrophysics, this technology has obtained development by leaps and bounds since middle 1980s, and the each scientific and technological power of the world including China has set up large-scale high power ultra-short pulse laser facility in succession.In femtosecond magnitude ultrafast laser system, it is main technology path that the chirped pulse based on titanium jewel (Ti:Sapphire) crystal amplifies (CPA); And large-aperture KDP crystal is the main frequency-doubling crystal of 1053nm fundamental frequency light, so the output efficiency that improves as much as possible KDP crystal is to improve pump energy, realize one of gordian technique of high energy laser output.
Be afraid of watt at high energy PW() in laser system, the method for optimizing KDP crystal double frequency efficiency is mainly to regulate phase matching angle and the position angle of KDP crystal to make frequency doubled light output efficiency maximum; The party's ratio juris can be summarized as follows:
The expression formula of II class KDP crystal double frequency is o+e → e, and the shg efficiency of KDP crystal is relevant with light transmition direction (θ, φ), deff=(d
14+ d
36) sin θ cos θ cos2 φ, optimum phase matching problem is exactly in the situation that phase matching angle θ is satisfied, selects the position angle φ of light transmition, makes the shg efficiency of KDP crystal reach maximum.Figure (1) has provided the frequency multiplication process of fundamental frequency light in KDP crystal; θ in figure is phase matching angle, and for fundamental frequency optical propagation direction is with respect to the angle of optical axis of crystal Z direction, φ angle is that light is at the projection of xy plane and the angle of optical axis.Regulate in order to reduce reflection loss and to be convenient to, in experiment, general total hope allows fundamental frequency light positive incident plane of crystal.So when processing frequency-doubling crystal, must press certain orientation sliced crystal, so that crystal normal direction becomes θ with optical axis direction, see figure (2).Therefore, in the time regulating the phase matching angle of KDP crystal, as long as make fundamental frequency light vertical incidence to plane of crystal.But owing to there being mismachining tolerance, be incident to after plane of crystal at definite fundamental frequency light positive, still need to finely tune phase matching angle and make KDP crystal reach optimum matching state; The fundamental frequency polarisation of light state of incident in II class frequency multiplication is 45
0line polarisation, when output light is horizontal polarization light or vertical polarization light time, now corresponding position angle φ is 0 ° or 90 °, known according to the expression formula of effective nonlinear coefficient, effective nonlinear coefficient maximum now, conversion efficiency is the highest.When the polarization state of frequency doubled light is not during at this two states, crystal is not in best frequency multiplication state, and output efficiency is on the low side.By rotating crystal, can change azimuthal size, and output polarisation of light state changes with the change at phasing degree.
At present, in high energy PW laser system, the key step of the control method of heavy caliber KDP frequency-doubling crystal can be summarized as follows: KDP frequency-doubling crystal is placed on after amplifier, makes light be incident to germ nucleus; Adjust phase matching angle and the position angle of KDP crystal, the power of simultaneously observing green glow with blank sheet of paper after KDP, until green glow stops the rotation when the strongest, fixes KDP crystal frame; Mainly there is following shortcoming in the method: due to only invisible light of fundamental frequency, and general KDP plane of crystal is all coated with 1053nm anti-reflection film, directly observe fundamental frequency only no vertical incidence plane of crystal be very difficult; Utilize the power of eye-observation green glow to be easy to cause eye fatigue, and then cause and judge inaccurately, affected frequency multiplication output; Even in the time that the green glow of exporting is the strongest, corresponding not necessarily horizontal polarization light of output polarisation of light state, is likely also orthogonal polarized light; The method need to be carried out the experiment of single-shot repeatedly just can obtain higher shg efficiency, consuming time very long, and shg efficiency can not get maximizing, and can not guarantee to export polarisation of light state.
Summary of the invention
The object of the invention is to overcome the shortcoming of above-mentioned existing heavy caliber KDP frequency-doubling crystal control method; The control method of a kind of II class KDP crystal to infrared light frequency multiplication optimum matching state is provided, and the method both can make shg efficiency maximize, and can guarantee to export again the control method of polarization state, and the method is simple to operate, scientific and effective not only, and practical.
Technical solution of the present invention is as follows:
The control method of II class KDP crystal to infrared light frequency multiplication optimum matching state, is characterized in that the method comprises the following steps:
1. prepare: in the near infrared fundamental frequency light light path that KDP crystal is set, the first aperture and second orifice diaphragm are placed respectively in two positions of the light path before KDP crystal design position, when utilizing infrared light detecting sheet to survey basic frequency beam, adjust the first aperture and second orifice diaphragm, make the center of described basic frequency beam through described the first aperture and second orifice diaphragm, to determine fundamental frequency direction of light;
2. the phase matching angle of coarse adjustment KDP crystal: placed He-Ne laser instrument before fundamental frequency light light path neutralizes the first aperture, regulate the adjustment rack of described He-Ne laser instrument, make the He-Ne laser beam of He-Ne laser instrument output by described the first aperture and second orifice diaphragm, now He-Ne laser beam overlaps with fundamental frequency light direction; To be fixed on KDP crystal on adjustment rack and be placed on the design attitude of KDP crystal in the light path after second orifice diaphragm, and make He-Ne laser beam be incident to the center of KDP crystal, by regulating pitching and the deflection of adjustment rack of KDP crystal, make the center superposition with described second orifice diaphragm from the He-Ne light beam of KDP plane of crystal reflection, the then adjustment rack of the KDP crystal described in locking;
3. regulate the position angle of KDP crystal: described He-Ne laser instrument, the first aperture and second orifice diaphragm are removed, opened fundamental frequency light, described fundamental frequency light has faint green glow output after described KDP crystal; A long focus lens is placed in the light path after described KDP crystal, near the focus of described long focus lens, place Rochon prism, rotate described KDP crystal by adjustment rack, after described Rochon prism, utilize white to observe green glow, in the time that the luminous point of green glow is unique, locking KDP crystal;
4. the phase matching angle of accurate adjustment KDP crystal: place photoelectric probe in the light path after described Rochon prism, the output terminal of described photoelectric probe is connected with oscillographic input end, the output of described photoelectric probe is input in oscillograph, then finely tune the adjustment rack pitching of KDP crystal and deflection, when waveforms amplitude on observation oscilloscope reaches maximum, the adjustment rack of fixing described KDP crystal, regulates completely, and described long focus lens, Rochon prism, photoelectric probe and oscillograph are removed.
Compared with first method, the present invention has following outstanding feature:
1, utilize visible He-Ne light to determine phase matching angle as secondary light source, very effectively simple in the time observing KDP plane of crystal light echo, can save the plenty of time;
2, utilize Rochon prism to judge the optimum azimuth of KDP crystal, accuracy is high, and maximum can reach desirable position angle, thereby has ensured that the green glow of output is the strongest, and shg efficiency is maximized;
3, utilize Rochon prism to guarantee the horizontal polarization state of frequency doubled light, ensured the absorption maximum of laser crystal to pump light, thereby can improve the amplification efficiency of final seed light.
Brief description of the drawings
Fig. 1 is o light and the e light in KDP uniaxial crystal.
Fig. 2 is the cutting of nonlinear crystal.
Fig. 3 is the simple and easy index path of the control method of II class KDP crystal of the present invention to infrared light frequency multiplication optimum matching state.
Embodiment
Below in conjunction with embodiment and accompanying drawing, the invention will be further described, but should not limit the scope of the invention with this.
First refer to Fig. 3, Fig. 3 is the simple and easy index path of the control method of II class KDP crystal of the present invention to infrared light frequency multiplication optimum matching state.The control method of II class KDP crystal of the present invention to infrared light frequency multiplication optimum matching state, comprises the following steps: as seen from the figure
1. prepare: in the near infrared fundamental frequency light light path (light beam working direction from left to right) that KDP crystal is set, the first aperture 2 and second orifice diaphragm 3 are placed respectively in two positions of the light path before KDP crystal, when utilizing infrared light detecting sheet to survey basic frequency beam, adjust the first aperture 2 and second orifice diaphragm 3, make the center of described basic frequency beam through described the first aperture 2 and second orifice diaphragm 3, to determine fundamental frequency direction of light;
2. the phase matching angle of coarse adjustment KDP crystal: placed He-Ne laser instrument 1 before fundamental frequency light light path neutralizes the first aperture 2, regulate the adjustment rack of described He-Ne laser instrument 1, make the He-Ne laser beam that He-Ne laser instrument 1 is exported pass through described the first aperture 2 and second orifice diaphragm 3, now He-Ne laser beam overlaps with fundamental frequency light direction; The KDP crystal 4 being fixed on adjustment rack is placed in the rear light path of second orifice diaphragm 3, and make He-Ne laser beam be incident to the center of KDP crystal 4, by regulating pitching and the deflection of adjustment rack of KDP crystal 4, make from the center superposition of the He-Ne light beam of KDP crystal 4 surface reflections and described second orifice diaphragm 3, the then adjustment rack of fixing described KDP crystal 4;
3. regulate the position angle of KDP crystal: described He-Ne laser instrument 1, the first aperture 2 and second orifice diaphragm 3 are removed, opened fundamental frequency light, described fundamental frequency light has faint green glow output after described KDP crystal 4; A long focus lens 5 is placed in the light path after described KDP crystal 4, near the focus of described long focus lens 5, place Rochon prism 6, by adjustment rack around the KDP crystal 4 described in Beam rotation, observe green glow at the rear utilization white of described Rochon prism 6 screen, in the time that the luminous point of green glow is unique, locking KDP crystal 4;
4. the phase matching angle of accurate adjustment KDP crystal: place photoelectric probe 7 in the light path after described Rochon prism 6, the output terminal of described photoelectric probe 7 is connected with the input end of oscillograph 8, the output of described photoelectric probe 7 is input in oscillograph 8, then finely tune 4 adjustment rack pitching and the deflections of KDP crystal, when waveforms amplitude on observation oscilloscope 8 reaches maximum, the adjustment rack of the KDP crystal described in locking, regulate completely, described long focus lens 5, Rochon prism 6, photoelectric probe 7 and oscillograph 8 are removed.
Claims (1)
1. the control method of II class KDP crystal to infrared light frequency multiplication optimum matching state, is characterized in that the method comprises the following steps:
1. prepare: in the near infrared fundamental frequency light light path that KDP crystal is set, the first aperture (2) and second orifice diaphragm (3) are placed respectively in two positions of the light path before KDP crystal, when utilizing infrared light detecting sheet to survey basic frequency beam, adjust the first aperture (2) and second orifice diaphragm (3), make the center of described basic frequency beam through described the first aperture (2) and second orifice diaphragm (3), to determine fundamental frequency direction of light;
2. the phase matching angle of coarse adjustment KDP crystal: neutralize the first aperture (2) in fundamental frequency light light path and place before He-Ne laser instrument (1), regulate the adjustment rack of described He-Ne laser instrument (1), make the He-Ne laser beam of He-Ne laser instrument (1) output by described the first aperture (2) and second orifice diaphragm (3), now He-Ne laser beam overlaps with fundamental frequency light direction; The KDP crystal (4) being fixed on adjustment rack is placed in the rear light path of second orifice diaphragm (3), and make He-Ne laser beam be incident to the center of KDP crystal (4), by regulating pitching and the deflection of adjustment rack of KDP crystal (4), make from the center superposition of the He-Ne light beam of KDP crystal (4) surface reflection and described second orifice diaphragm (3), the then adjustment rack of fixing described KDP crystal (4);
3. regulate the position angle of KDP crystal: described He-Ne laser instrument (1), the first aperture (2) and second orifice diaphragm (3) are removed, open fundamental frequency light, described fundamental frequency light has faint green glow output after described KDP crystal (4); A long focus lens (5) is placed in the light path after described KDP crystal (4), near the focus of described long focus lens (5), place Rochon prism (6), rotate described KDP crystal (4) by adjustment rack, after described Rochon prism (6), utilize white screen to observe green glow, in the time that the luminous point of green glow is unique, the rotation knob of the adjustment rack of locking KDP crystal (4);
4. the phase matching angle of accurate adjustment KDP crystal: place photoelectric probe (7) in the light path after described Rochon prism (6), the output terminal of described photoelectric probe (7) is connected with the input end of oscillograph (8), the output of described photoelectric probe (7) is input in oscillograph (8), then finely tune KDP crystal (4) adjustment rack pitching and deflection, when waveforms amplitude on observation oscilloscope (8) reaches maximum, the adjustment rack of the KDP crystal described in locking, regulate complete, by described long focus lens (5), Rochon prism (6), photoelectric probe (7) and oscillograph (8) are removed.
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| CN103278997B (en) * | 2013-04-28 | 2016-01-20 | 哈尔滨工业大学 | A kind of mixer crystal four-dimensional high-precision adjustment mechanism |
| CN103278128B (en) * | 2013-05-17 | 2015-11-04 | 中国工程物理研究院激光聚变研究中心 | One is KDP crystal optimum matching angle accurate measurement method fast |
| CN103457146B (en) * | 2013-09-05 | 2015-12-23 | 中国科学院上海光学精密机械研究所 | Determine titanium gem crystal crystallographic axis towards method |
| CN108168470B (en) * | 2018-03-21 | 2023-07-04 | 中国工程物理研究院激光聚变研究中心 | Device and method for measuring characteristic angle of frequency doubling crystal based on divergent light beam |
| CN111244731A (en) * | 2018-11-28 | 2020-06-05 | 中国科学院大连化学物理研究所 | Crystal constant temperature equipment with adjustable angle |
| CN111913332A (en) * | 2020-08-17 | 2020-11-10 | 江苏博创翰林光电高科技有限公司 | Second harmonic bandwidth compression method |
| CN114414210B (en) * | 2021-11-25 | 2023-03-21 | 清华大学 | Rapid measurement system and method for phase matching direction of laser frequency doubling crystal |
| CN114413794B (en) * | 2022-01-29 | 2023-09-22 | 中国工程物理研究院激光聚变研究中心 | System and method for measuring optimal phase matching angle of large-caliber KDP crystal |
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| CN2629933Y (en) * | 2003-03-17 | 2004-08-04 | 中国科学院福建物质结构研究所 | Adjustable cutting device of double-frequency crystal I phase matching angle |
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| US7433373B2 (en) * | 2004-06-15 | 2008-10-07 | National Tsing Hua University | Actively Q-switched laser system using quasi-phase-matched electro-optic Q-switch |
| US8102593B2 (en) * | 2007-08-07 | 2012-01-24 | Onyx Optics, Inc. | Quasi non-critical phase matched and contra-phase matched structures |
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