JPH01163631A - Weak light measuring instrument with mode switching function - Google Patents

Abstract

PURPOSE:To easily measure weak light by bringing microchannel plates (MCP) under feedback control according to the output of a high-sensitivity multichannel detector (IMD) and switching measurement modes. CONSTITUTION:An integration time, etc., is brought under the feedback control of a control circuit 21 according to the incident light detection output of the IMD 11 passed through a sample and hold circuit 17 and the MCP for optical multiplication of the IMD 11 are placed in a 80% saturation state. When the output of the circuit 17 is large, an analog mode measurement is taken by the circuit 21, a switch circuit 19, etc., through an A/D converter 23. The MCPs are placed in a saturation state according to switching and a digital mode measurement is take through a CT counter 27; when the output of the circuit 17 becomes larger than a set value, switching is carried out through a comparator 25 to perform switching to the analog measurement mode by the circuits 21 and 19 according to the ratio of the counted value of a CF counter 29 counting double photons and the sum of the outputs of counters 27 and 29. Thus, the measurement modes are switched automatically to easily take a measurement in the best short integration time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a weak light measuring device having a mode switching function for automatically switching between an analog mode and a counting mode to measure weak light.

[Conventional technology]

Figure 7 shows an image intensifier and a PCD (Plasuma-Co), which is a self-scanning linear image sensor.
A conventional high-sensitivity multichannel photodetector (uploaded device), high-voltage power supply, and drive circuit (
Intensified Multichannel
Detect.

r, hereinafter referred to as IMD). In the figure, 101 is a spectrometer, 103 is a +MD, 105 is an image intensifier, 107 is a photocathode, 109 is a mesh electrode, 111.
113 is a focusing electrode, 115 is a microchannel plate 1- (MCP), 117 is a fluorescent surface, 119 is a high voltage power supply, 121 is a fiber plate, 123 is a PCD, 1
25 is a PCD driving circuit, 127 is an integrating circuit, and 129 is an amplifier.

In the figure, the weak spectrum I and
The image is the photocathode 10 of the image intensifier 105.
7, is converted into photoelectrons, accelerated by the mesh electrode 109, and sent to the MCP 11 via the focusing electrodes 111 and 113.
5, the incident light is multiplied several thousand times or more as it passes through the inside of the MCP 115, collides with the fluorescent surface 117, and is converted into an optical image again, and as a result, the incident light is multiplied tens of thousands of times. It will be strengthened.

The enhanced spectral image is the fiber plate 121
is guided to PCD123 with high efficiency, and 51 in the wavelength direction.
It is output as independent time-series electrical signals of 2 or 1024 channels.

The PCD is driven by master clocks C1, . . . K and a start pulse synchronized therewith, and the output signal is read out as a video output at a transfer rate of 4 CL K per channel and at the period of the start pulse. Since the signal is integrated during the readout period, it becomes possible to read out a weak optical image such as a light spectrum.

[Problems to be solved by the invention]

In such conventional IMDs, since the image intensifier has only one MCP, the light amplification degree is only tens of thousands of times, so when the input light becomes weak, the P
The light sent to the CD becomes weaker, so the PCD side must increase the integration time to extract this signal. However, if the integration time is lengthened, the signal will be buried by leakage current generated from the PCD itself, so we try to shorten the integration time by increasing the gain even a little.
There was a problem in that it required skill and lacked operability.

The present invention is intended to solve the above-mentioned problems. It is possible to increase the degree of photointensification and set the integration time to be short, eliminate the influence of leakage current, and eliminate the charge saturation phenomenon caused by increasing the degree of photointensification. An object of the present invention is to provide a weak light measuring device which is equipped with a mode switching function that can be used to perform measurements in a counting mode and to automatically switch between an analog mode and a counting mode.

[Means for solving problems]

To this end, the present invention provides a photocathode, an electron optical system that forms an electron image using electrons emitted from the photocathode, and a secondary electron multiplier that multiplies photoelectrons while maintaining their two-dimensional position. , an apparatus for performing optical measurement using an electron tube having a detection element array for detecting multiplied electrons, comprising a control means for controlling the drive voltage of the electron tube, the control means controlling the output of the maximum output channel of the detection element array; The secondary electron multiplier drive voltage is controlled to be a predetermined ratio of the saturation value to set 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 is multiplied. The drive voltage is set so as to saturate the device, and the mode is switched to the counting mode. In the counting mode, when the output of the maximum output channel of the detection element array is equal to or greater than a predetermined value, the switching to the analog mode is performed. Features.

[Effect]

The present invention uses a highly sensitive 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 detection element array becomes approximately 80% of the saturation value. Measurement is performed in analog mode by controlling the driving voltage of the secondary electron multiplier as shown in FIG. Set the voltage to a large value, saturate it, and switch to measurement in counting mode. In counting mode, when the output of the maximum output channel of the detection element array exceeds a predetermined value at a predetermined rate or more, switch to analog mode and measure the weak signal. It becomes possible to automatically measure light.

〔Example〕

Examples will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of a weak light measuring device equipped with a mode switching function according to the present invention, and FIG. 2 shows a partial configuration of an embodiment of an image intensifier used in the present invention. , is a diagram showing drive voltages in analog mode and counting mode. In the figure, 11 is IM
D, 13 is a power supply, 15 is an amplifier, 17 is a sample and 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, 2
9 is a CF counter, 31 is a cathode, 33 is a mesh electrode 1.35 is a focusing electrode, 37 is an MCP, 39 is a screen electrode, 41 is a power source for the cathode, 43 is a power source for MCP,
45 is a power source for the screen.

IMDll in this embodiment is IMD103 in FIG.
The structure is similar to that of the above, but the difference is that an image intensifier having two MCPs is used and the gain is increased to 106 as shown in FIG.

In this way, it is possible to make the light up to 100 times brighter than in an IMD using a conventional image intensifier, and the integration time can be shortened to reduce the influence of leakage current.

By the way, in the case of an MCPI chip, the gain can only be increased to about 104 at most, but the input/output characteristics maintain linearity, and if one electron enters one channel of the MCP, 104 will be output. If 10 electrons enter, 10
5 electrons are output, but if the gain is increased to 106, the MCP will be in a saturated state, and even if one or two electrons enter one channel, the output will not be the same. The amount of charge becomes the same as 106 electrons, and it takes several tens of m5ec to recover.

Therefore, in the present invention, when the amount of light is relatively large, the driving voltage of the MCP is adjusted to 1 to 1.5, for example, as shown in FIG.
KV, set it to a small value, lower the gain, and measure the amount of incident light as a current value (analog mode). If the light is small, change the MCP drive voltage as shown in Figure 2 (b).
For example, set it to a large value of 1.9KV and increase the gain.
It is designed to detect whether or not a photon is incident in a saturated state (counting mode).

In FIG. 1, the PCD detection output of IMDII is amplified by an amplifier 15, sampled and held by a sample bold circuit 17, and is sent to a control circuit 21 having a built-in CPU, for example.
is loaded into. The control circuit 21 controls the power supply 13 based on the read value to control the degree of reinforcement of IMDII. In this case, feedback control is performed so that the PCD detection voltage becomes a predetermined ratio of the saturation value, for example, an appropriate value such as 80%, as will be described later. Further, the control circuit 21 determines based on the read value whether the amount of incident light is large and measurement using the analog mode is appropriate, or whether the amount of incident light is small and measurement using the counting mode is appropriate.
Switch. In the analog mode, the IMD output is applied to the A/D converter 23, A/D converted, and displayed or recorded with an ammeter or recorder (not shown). 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, the CT counter 27 counts, and if the PCD output is larger than the set value, the CF counter 29 counts 1-L, These values are read into the control circuit 21, and as will be described later, the ratio of the CT counter value to the sum of both is determined, and it is determined whether or not to switch to the analog mode based on the value of this ratio.

Next, switching between analog mode and counting mode will be explained.

Figure 3 is a diagram showing the relationship between the amount of incident light and the IMD output.Characteristic A is channel plate voltage Vmcp-1, OKV, screen voltage Vs=4KV, integration time "l"exp=1
0ms is shown, Vmcp and Vs are set low to reduce the degree of light amplification, and Texp is set to the minimum so that it can respond to the strongest light, up to 1.15X10
The linearity of the output voltage with respect to the amount of incident light is maintained up to 7 pe (electrons)/sec. Also, characteristic B is Vmcp=], 4KV, Vs=5KV,
When Texp=10ms, characteristic C is Vmcp-]
, 4KV, Vs=5KV, and Texp=100ms. In the case of characteristic C, the incident light is small, and Vmcp is set larger than in the case of characteristic A, but smaller than the saturation value, and the exposure time is lengthened to increase the time for integrating the incident light.

1. Regarding Ope/Sec, the MCP is driven in a saturated state with Vmcp set to 2KV. incident sight], IMD and Vm for p e / sec
The relationship with cp is as shown in Figure 4, for example],,9K
If it is more than V, it will be saturated. At this time, Vs is set in relation to the saturation value, and since saturation occurs even if one photon enters in this state, the integration time is kept to a minimum.

The range in which the incident sight can be measured using the linearity of these characteristics A to C is the analog mode region, and the best linearity is where the IMD output detected by the PCD is, for example, 80% of the saturation value. Vmcp is set. In this case, Vs is set to the maximum so as not to place a burden on the MCP. If the amount of incident light decreases in this state, the control circuit 21
will increase the value of 7m c p so as to maintain 80% of the pcD detected voltage force l inclusive value. Therefore, since there is a relationship between incident light and Vmcp such that Vmcp increases as the incident light becomes weaker, it becomes possible to determine how much incident light is present from Vmcp. Therefore, we measured the relationship between the incident light and Vmcp in advance, and
The number of incident electrons in the MCP of the peak channel of CL D is l
If Vmcp that results in Op e/sec is determined, it is possible to determine whether to switch from the analog mode to the counting mode by monitoring the value of Vmcp.

In addition, below 10 p e / sec, as mentioned above, Vs is adjusted and set in relation to the saturation voltage, and the integration time is set so that it is saturated even if one point is incident. Therefore, if this time is long, it will be difficult to know what has been detected, so the minimum time is 10 msec. Then, if the integration time is 10 m s e (closed, the probability of detecting a horn in one scan of the PCD is less than 0.1, and the output voltage for the frequency of incidence on one channel of the PCD is (charge amount) shows a single photon distribution as shown as a solid line in Figure 5.As the light increases, the PCD
Bottles are incident on a plurality of channels of the channel plate corresponding to one channel of , producing a double photon distribution shown by the broken line in FIG. Therefore, the detection output of the PCD and the PCDCD saturation lens are compared with a set level that is slightly lower than the PCDCD saturation lens, and depending on the proportion of these levels exceeded, it is possible to determine how much double photon distribution has occurred, that is, whether or not the light has increased. can be determined. Note that in the counting mode, if a double photon distribution is detected, this data is not adopted.

Next, the switching operation from analog mode to counting mode will be explained with reference to FIG. 6(a).

In Figure 6 (a), first reduce the burden on the MCP,
In order to improve linearity, set the screen voltage Vs to the maximum (for example, 6KV) (Step 2). Next, detect the output type pressure of the peak channel of the PCD and judge whether this value is, for example, 80% of the saturation value (steps The voltage Vmcp is controlled so that an appropriate output can be obtained (step 2). In the state where the PCD output power l is 80% of the envelope sum value, check whether the channel plate voltage ■mcp is larger than the predetermined set value (step ■), and if it is larger, the incident light amount is 10 p e / s e
Judging that it is less than c, switch to counting mode,
If it is small, return to step ■ and change Vmcp and IMD
Perform gain control 1~roll.

Next, switching from counting mode to analog mode will be explained with reference to FIG. 6(b).

First, to set the saturation region, Vmcp is set to the maximum, Vs, .
! : Set Texp to the minimum (step ■) and detect the peak channel PCD output (step knob ■). If the PCD output is larger than the set voltage, it is assumed that there is a double photon distribution, and the CF counter counts the steps (■).
If the PCD output is smaller than the set voltage, use the CT counter as a single-bottom distribution;! First step (■) is to calculate the ratio of the count value of the CT counter to the sum of these count values.If this is smaller than 0.5, for example, the ratio of double-bottom distribution exceeds 50%, and the light is Switch to analog mode because the number has increased,
If it is larger than 0 or 5, return to step 7b■. In the above explanation, an example has been described in which the IMD cane control in the analog mode is performed by changing Vmcp, but the integral time 'Fexp may also be made variable to control I/roll.

In addition, in the above embodiment, the case where i; There is no need to limit the detection element, and the detection element is not limited to the PCD element, but may be an optical or electronic detection element array such as a CCD. However, in the case of electronically detected
:J The detection section may be enclosed within the electron tube.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to increase the degree of photointensification and set the integration time to be short, eliminate the influence of leakage current, and perform counting by utilizing the charge saturation phenomenon caused by increasing the degree of photointensification. In addition to measuring in
Automatically switching between analog mode and counting mode makes it possible to easily measure weak light.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of a weak light measurement device with a mode switching function according to the present invention, and Figure 2 shows a partial configuration of an image intensifier and drive voltages in analog mode and counting mode. Figure 3 shows the relationship between the amount of incident light and the IMD output, and the fourth figure shows the relationship between the amount of incident light and the IMD output.
A diagram showing the relationship between TMD output and Vmcp with respect to the amount of incident light of p e / sec, Figure 5 is a diagram showing the relationship between incident frequency and charge amount, and Figure 6 explains the switching operation between analog mode and counting mode. diagram for,
FIG. 7 is a diagram showing the configuration of a conventional TMD. ]6 1]...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, 3]... Cathode, 33... Metosh electrode, 35... Focusing electrode, 37... MCP,
39... Screen electrode, 41... Power supply for cathode, 43... Power supply for MCP, 45... Power supply for screen. Applicant Hamamatsu Potonics Co., Ltd. Agent
Person Patent Attorney Hiru Kawa Masa Shin－緘（・い－；＼＋） 6th (A) (B) ■ Lips Ink "Geat"'Zeng Shao Fu VMCP
Max VSCRm1n Texp min ■ Cooling tank PCD output calibration ■ PCD insect power ≧ spider pressure N Go to 6 -1, 11. Back -7s'+ J+, Waniinshi ``7゛ノ'7 History 1 υノ/Tsuma゛ Seal
Heat (-ζ′old 4kumi■ CT ku05 N CT specialist CF

Claims (2)

[Claims] (1) A photocathode, an electron optical system that forms an electron image using electrons emitted from the photocathode, a secondary electron multiplier that multiplies photoelectrons while maintaining their two-dimensional position, and multiplication A device that performs optical measurement using an electron tube having a detection element array that detects electrons detected by The secondary electron multiplier drive voltage is controlled to be a predetermined ratio of The mode switching is characterized in that the driving voltage is set so as to cause the switching to the counting mode, and when the number of events in which the output of the maximum output channel of the detection element array exceeds a predetermined value exceeds a predetermined rate in the counting mode, the mode is switched to the analog mode. A weak light measurement device with various functions. (2) A weak light measuring device with a mode switching function according to claim 1, wherein the detection element array is an electronic detection element array or a photodetection element array.