JPH0814508B2 - Weak light measurement device with mode switching function - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a weak light measuring device having a mode switching function of automatically switching between an analog mode and a counting mode to measure weak light.

[Conventional technology]

Figure 7 shows the image intensifier and PCD (Plasuma-Coupled Devic) which is a self-scanning linear image sensor.
e), conventional high-sensitivity multi-channel photodetector (Intensified Multichannel) with built-in high voltage power supply and drive circuit
Detector, hereafter referred to as IMD). In the figure, 101 is a spectroscope, 103 is an IMD, 105 is an image intensifier, 107
Is a photocathode, 109 is a mesh electrode, 111 and 113 are focusing electrodes, 1
15 is a micro channel plate (MCP), 117 is a fluorescent surface, 119 is a high voltage power supply, 121 is a fiber plate, 123 is P
CD, 125 is a PCD driving circuit, 127 is an integrating circuit, and 129 is an amplifier.

In the figure, the weak spectrum image dispersed by the spectroscope 101 enters the photocathode 107 of the image intensifier 105, is converted into photoelectrons, and is accelerated by the mesh electrode 109,
The focusing electrodes 111 and 113 are imaged on the input surface of the MCP 115 via
When passing through the inside of the MCP 115, it is multiplied by several thousand times or more, collides with the fluorescent surface 117 and is converted into an optical image again, and as a result, the incident light is enhanced by tens of thousands of times. The enhanced spectral image is guided to the PCD 123 with high efficiency by the fiber plate 121, and is output as an independent time-series electric signal of 512 or 1024 channels in the wavelength direction.

The PCD is driven by the master clock CLK and a start pulse synchronized with the master clock CLK, and the output signal is read out as a video output at a transfer rate of 4 CLK per channel and at a cycle of the start pulse. Since the signals are integrated during the read cycle, a weak light image such as a light spectrum can be read.

[Problems to be solved by the invention]

In such a conventional IMD, since the image intensifier has only one MCP, the light intensity is only tens of thousands of times, and therefore the PCD becomes weak when the input light becomes weak.
The light sent to is weakened, so the integration time must be lengthened on the PCD side to extract this signal. However, if the integration time is lengthened, the signal will be buried by the leakage current generated from the PCD itself, so although the gain is increased to shorten the integration time, skill is required and operability is lacking. There was a problem.

The present invention is for solving the above-mentioned problems, and it is possible to set the integration time short by increasing the light enhancement level, eliminate the influence of leak current, and reduce the charge saturation phenomenon associated with the increase in the light enhancement level. It is an object of the present invention to provide a weak light measurement device equipped with a mode switching function capable of automatically performing switching between an analog mode and a counting mode while performing a measurement in a counting mode by utilizing it.

[Means for solving problems]

To this end, the present invention provides a photocathode, an electron optical system that forms an electron image of electrons emitted from the photocathode, and a secondary electron multiplier that multiplies photoelectrons while maintaining a two-dimensional position. In an apparatus for performing optical measurement by an electron tube having a detection element array for detecting multiplied electrons, the control means is provided with a control means for controlling a driving voltage of the electron tube, and the control means outputs the maximum output channel of the detection element array. The secondary electron multiplier drive voltage is controlled so that becomes a predetermined ratio of the saturation value to enter the analog mode, and in the analog mode, when the secondary electron multiplier drive voltage is equal to or higher than the predetermined value, the secondary electron multiplier There is an event that the output of the maximum output channel of the detector array exceeds a specified value in the counting mode by setting the drive voltage to saturate the detector and switching to the counting mode. And it switches the analog mode when the above ratio.

[Action]

The present invention uses a high-sensitivity multi-channel photodetector having a secondary electron multiplier with a large gain, and when the amount of incident light is large, the output of the maximum output channel of the detector array becomes about 80% of the saturation value. The secondary electron multiplier drive voltage is controlled as described above to perform measurement in the analog mode, and the secondary electron multiplier drive is performed on condition that the secondary electron multiplier drive voltage is equal to or higher than a predetermined value in the analog mode. Set the voltage to a high value, saturate it, and switch to measurement in counting mode. In counting mode, when the output of the maximum output channel of the detector array exceeds a specified value, the event is switched to analog mode and weak It becomes possible to perform automatic measurement of light.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an embodiment of a weak light measuring device having a mode switching function according to the present invention, and FIG.
The figure is a diagram showing a part of the configuration of an embodiment of the image intensifier used in the present invention and the drive voltage in the analog mode and the counting mode. In the figure, 11 is IM
D, 13 is a power supply, 15 is an amplifier, 17 is a sample hold circuit, 19 is a switch circuit, 21 is a control circuit, 23 is an A / D converter, 25 is a comparator, 27 is a CT counter, 29 is a CF counter, 31
Is a cathode, 33 is a mesh electrode, 35 is a focusing electrode, and 37 is a MC
P, 39 are screen electrodes, 41 is cathode power supply, 43 is MCP
And 45 is a screen power supply.

The IMD 11 in this embodiment has the same structure as the IMD 103 in FIG. 7, but as shown in FIG. 2, an image intensifier having two MCPs is used to increase the gain up to 10 ⁶ . Are different. This way IMDs using traditional image intensifiers
It is possible to illuminate up to 100 times brighter than the above, and it is possible to reduce the influence of leak current by shortening the integration time accordingly.

By the way, in the case of one MCP, the gain can be increased up to about 10 ⁴ at most, but the linearity of the input / output characteristics is maintained, and if one electron enters one channel of the MCP, it becomes 1
While 0 ⁴ is output and 10 electrons are input, 10 ⁵ is output, whereas when the gain is increased to 10 ⁶ , the MCP becomes saturated and one is output to one channel. Even if an electron enters, even if two electrons enter, the output will be 10 ⁶ electrons and the charge amount will be uniform, and it will take several tens of milliseconds to recover.

Therefore, in the present invention, when the amount of light is relatively large, the driving voltage of the MCP is set to, for example, 1 to 1.5 KV as shown in FIG.
Set the value to a small value and decrease the gain to measure the incident light amount as a current value (analog mode). If the light is low, set the MCP drive voltage to, for example, 1.9KV as shown in Fig. 2 (b). Is set to a large value and the gain is increased to a saturated state to detect whether or not a photon is incident (counting mode).

In FIG. 1, the PCD detection output of the IMD 11 is amplified by the amplifier 15, sample-held by the sample-hold circuit 17, and read into the control circuit 21 including a CPU, for example. The control circuit 21 controls the power supply 13 according to the read value.
Controls IMD11 gain. In this case, P
Feedback control is performed so that the CD detection voltage becomes a predetermined ratio with respect to the saturation value, for example, an appropriate value such as 80%. The control circuit 21 determines whether the amount of incident light is large and the measurement in the analog mode is appropriate or the amount of incident light is small and the measurement in the counting mode is appropriate based on the read value, and switches the switch circuit 19. In the analog mode, the IMD output is A / D converted in addition to the A / D converter 23 and displayed or recorded by an ammeter, a recorder or the like not shown. Also, in counting mode, the comparator 25 compares the PCD output with the set value, and if the PCD output is smaller than the set value, C
The T counter 27 counts, and if the PCD output is larger than the set value, the CF counter 29 counts these values, and these values
The value is read in 21 and the ratio of the value of the CT counter to the sum of the two is calculated as will be described later. Based on the value of this ratio, it is determined whether or not to switch to the analog mode.

Next, switching between the analog mode and the counting mode will be described.

Fig. 3 shows the relationship between the amount of incident light and the IMD output. Characteristic A shows the case where the channel plate voltage Vmcp = 1.0KV, the screen voltage Vs = 4KV, and the integration time Texp = 10ms.
With p and Vs set low to reduce the light intensity, and Texp set to the minimum so that it can handle the strongest light,
The linearity of the output voltage with respect to the incident light quantity is maintained up to 1.15 × 10 ⁷ pe (photoelectrons) / sec. Characteristic B is
Characteristic C is when Vmcp = 1.4KV, Vs = 5KV, Texp = 10ms
The case where Vmcp = 1.4 KV, Vs = 5 KV, and Texp = 100 ms is shown. In the case of the characteristic C, when the incident light is small, Vmcp is set to be larger than that of the characteristic A but smaller than the saturation value, and the exposure time is lengthened to increase the time for integrating the incident light.

At 10pe / sec, MCP is driven in a saturated state with Vmcp set to 2KV. The relationship between IMD and Vmcp with respect to the incident light amount of 1 pe / sec is as shown in FIG. 4, and is saturated if it is 1.9 KV or more, for example. At this time, Vs is set in relation to the saturation value, and in this state, even if one photon enters, it is saturated, so the integration time is set to the minimum.

The range in which the amount of incident light can be measured using the linearity of these characteristics A to C is the analog mode region, and the IMD output detected by the PCD has the best linearity, for example, 80% of the saturation value. Is set to Vmcp. In this case, Vs is
It is set to the maximum so as not to burden the MCP. When the amount of incident light decreases in this state, the control circuit 21 increases the value of Vmcp so that the PCD detection voltage maintains 80% of the saturation value. Therefore, since the incident light and Vmcp have a relationship that Vmcp increases when the incident light becomes weaker, it is possible to determine how much the incident light is from Vmcp.
Therefore, the relationship between the incident light and Vmcp was measured in advance, and the number of incident electrons in the MCP of the PCD peak channel was 10 pe / s.
If Vmcp that becomes ec is obtained, the switching from the analog mode to the counting mode can be determined by monitoring the value of Vmcp.

At 10 pe / sec or less, Vs is adjusted and set in relation to the saturation voltage as described above, and the integration time is 1
Since it is in a saturated state even when it is individually incident, if it is long, it will not be known what was detected, so the minimum is 10 msec. When the integration time is 10 msec, the probability of detecting photons in one scan of PCD is 0.1 or less,
The output voltage (charge amount) with respect to the incident frequency in one channel of D shows a single photon distribution as shown by the solid line in FIG. When the amount of light increases, photons are incident on the channels of the channel plate corresponding to one channel of the PCD, and the double photon distribution shown by the broken line in FIG. 5 is generated. Therefore, compare the detection output of the PCD with the PCD saturation level or a setting level slightly lower than the PCD saturation level to determine how much the double photon distribution has occurred, that is, whether the light has increased or not depending on the ratio exceeding these levels. Can be determined. In the counting mode, this data is not used when the double photon distribution is detected.

Next, the switching operation from the analog mode to the counting mode will be described with reference to FIG.

In Fig. 6 (a), first reduce the load on the MCP,
The screen voltage Vs is set to the maximum (for example, 6 KV) to improve the linearity (step). Next, the output voltage of the peak channel of the PCD is detected, and it is judged whether this value is, for example, 80% of the saturation value (step,),
If it is not 80%, control the channel plate voltage Vmcp so that an appropriate output is obtained (step). While the PCD output is at 80% of the saturation value, check if the channel plate voltage Vmcp is larger than the preset value (step), and if it is larger, judge that the incident amount is 10 pe / sec or less and count mode Switch to, if it is smaller, go back to step and change Vmcp and IMD
Gain control of.

Next, switching from the counting mode to the analog mode will be described with reference to FIG.

First, Vmcp is set to the maximum and Vs and Texp are set to the minimum to set the saturation region (step), and the peak channel PCD output is detected (step). If the PCD output is larger than the installation voltage, it is counted as a double photon distribution by the CF counter (step), and if the PCD output is smaller than the set voltage, it is counted as a single photon distribution by the CT counter (step) and the sum of these count values is calculated. Calculate the ratio of the count value of the CT counter to (step). If this is less than 0.5, the ratio of the double photon distribution is 50%.
If it is above 0.5, the mode is switched to analog mode, assuming that the light level is high, and if it is greater than 0.5, the process returns to step. In the above description, IMD in analog mode
Although the example in which the gain control is performed by changing Vmcp has been described, the integration time Texp may be variable and controlled.

Further, in the above-described embodiment, the case where the number of MCPs is two has been described, but the point is that the gain is 2 as compared with the case of one conventional MCP.
It is not necessary to limit the number of MCPs as long as it is larger than a digit, and the detection element is not limited to the PCD element, and other optical or electronic detection element array such as CCD may be used. However, in the case of electronic detection, the detection unit may be enclosed in the electron tube.

〔The invention's effect〕

As described above, according to the present invention, the photointensity can be increased and the integration time can be set to be short, the influence of the leakage current can be eliminated, and the charge saturation phenomenon associated with the increase in the photointensity can be used for counting. It becomes possible to perform the measurement in the mode and automatically switch the analog mode and the counting mode to easily measure the weak light.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a weak light measuring device having a mode switching function according to the present invention, and FIG. 2 shows a partial configuration of an image intensifier and driving voltages in an analog mode and a counting mode. Figures and 3 show the relationship between the amount of incident light and IMD output, and Figure 4 shows 1pe / sec.
Shows the relationship between the IMD output and Vmcp with respect to the incident light amount, FIG. 5 shows the relationship between the incident frequency and the charge amount, FIG. 6 shows the switching operation between the analog mode and the counting mode, FIG. FIG. 7 is a diagram showing a configuration of a conventional IMD. 11 …… IMD, 13 …… Power supply, 15 …… Amplifier, 17 …… Sample hold circuit, 19 …… Switch circuit, 21 …… Control circuit, 23 …… A / D converter, 25 …… Comparator, 27 ...... CT counter, 29 …… CF counter, 31 …… cathode, 33 …… mesh electrode, 35 …… focusing electrode, 37 …… MCP, 39 …… screen electrode, 41 …… cathode power supply, 43 …… MCP For power, 45
…… Screen power supply.

Claims (2)

[Claims] 1. A photocathode, an electron optical system for forming an electron image by electrons emitted from the photocathode, a secondary electron multiplier for multiplying photoelectrons while maintaining a two-dimensional position. In an apparatus for performing optical measurement by an electron tube having a detection element array for detecting multiplied electrons, a control means for controlling a driving voltage of the electron tube is provided, and the control means controls the output of the maximum output channel of the detection element array. The secondary electron multiplier drive voltage is controlled so that it becomes a predetermined ratio of the saturation value to enter the analog mode, and when the secondary electron multiplier drive voltage is equal to or higher than the predetermined value in the analog mode, the secondary electron multiplier The drive voltage is set to saturate the sensor, and the mode is switched to the counting mode. Weak light measuring apparatus equipped with a mode switching function, characterized in that to switch to analog mode when. 2. The weak light measuring device having a mode switching function according to claim 1, wherein the detecting element array is an electronic detecting element array or a photodetecting element array.