JPH0230447B2 - NIJIGENBIJAKUGAZOKEISOKUSOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides two-dimensional weak image measurement for measuring two-dimensional weak images whose single photon input, which is the basis of image composition, is in two-dimensional resolution units and is below the level that can be resolved in time. Regarding equipment.

2. Description of the Related Art Conventionally, as a device for detecting a weak optical image, a television imaging device using an ultra-high-sensitivity photographed image is known.

The apparatus includes a photocathode as an imaging tube, a silicon semiconductor target provided opposite to the photocathode, a silicon multiplier vidicon having an electron gun for scanning the silicon semiconductor target with an electron beam, and further in front of the photocathode. A silicon intensifying vidicon equipped with an image intensifier tube is used.

The lower limit illuminance at which an image can be captured by the above-mentioned television imaging device is from several millilux to a fraction of a millilux. If this illuminance is expressed as the number of photons incident on the photocathode, it corresponds to 10 ⁹ to 10 ⁸ photons/(cm ² seconds). In this type of device, if the reading operation is interrupted while an optical image is incident, a signal corresponding to the incident optical image can be accumulated on the target, thereby increasing the sensitivity. However, there are disadvantages such as the accumulation of thermoelectrons generated at the photocathode and the target, and the leakage of charges accumulated in the target. As a result, even if the sensitivity is improved, the problem of poor contrast and image quality remains. Furthermore, an image pickup tube using the above-mentioned target essentially has a small dynamic range, and even if the dynamic range is relatively large, it does not exceed 10 ³ .

In order to measure images of lower illuminance that cannot be captured with the above-mentioned device while maintaining a satisfactory contrast, the inventor of the present invention determined the photoelectron generation position by changing the incident location of photons in units of single photoelectrons generated from the photocathode. We focused on the fact that it is possible to measure a weak two-dimensional image by identifying and counting the frequency of photoelectron generation from each generation position. When trying to realize the above idea using an image tube having a photocathode, a microchannel plate, and a semiconductor position detection device, which will be described later, there were two basic problems that had to be solved.

The first problem is the signal caused by a single photon that is multiplied by the microchannel plate and whose position is determined by the semiconductor position detector, and the thermal noise caused by the microchannel plate, semiconductor position detector, etc. themselves. It is to distinguish between

The second problem is that even if the average value of the generation interval of single photoelectrons generated from the entire surface of the photocathode of the image tube is sufficiently time-resolvable, it may become partially time-resolvable. It is.

When inputs caused by two or more single photoelectrons occur within a fixed period of time that cannot be resolved, the semiconductor position detection device outputs information on an average position that is not one of the respective incident positions. Therefore, if the generation interval of a single photoelectron cannot be resolved in time by the semiconductor position detection device, the semiconductor position detection device may output noise that is unrelated to the image even though the input signal is caused by the photoelectrons. become. The second problem will be referred to as the problem of signal-specific noise.

This signal-specific noise problem is less fundamental than the first device-specific noise problem, and is an acceptable problem in some cases, where the probability of time resolution failure is extremely low.

The inventors of the present invention solved the problem of noise inherent in the device as follows.

The multiplication factor of the microchannel plate is selected such that the microchannel plate amplifies photoelectrons due to single photons sufficiently to distinguish them above the noise level inherent in the device, and the variation in the multiplication factor is extremely small. I did it like that. The signals are then separated by a pulse height selector having a threshold between the signal caused by a single photon and the noise inherent in the device.

The problem of noise inherent in the signal is also solved as follows. When the outputs of the microchannel plate caused by two or more photoelectrons are incident on the semiconductor position detection device simultaneously or at intervals that cannot be resolved in time, the output of the semiconductor position detection device is smaller than that in the case of a single photoelectron. growing. Therefore, it can be separated by a pulse height selector with a threshold that lies between the signal due to single photons and the noise inherent in the signal.

The main object of the present invention is to produce a two-dimensional image in which the input of a single photoelectron is so weak that it can be time-resolved within a two-dimensional resolution unit, for example, 1/10 of the lower limit illuminance at which the above-mentioned television imaging device can image. The object of the present invention is to provide a two-dimensional weak image measuring device that can measure two-dimensional weak images with an illuminance of ³ to 1/10 ⁸ while maintaining good contrast.

Another object of the present invention is to provide a two-dimensional weak image measuring device that solves the problems of noise inherent in the device and noise inherent in the signal.

Still another object of the present invention is to provide a two-dimensional weak image measuring device equipped with an output device capable of outputting data of the results of the two-dimensional weak image measurement or measurement images of the measurement process in real time. be.

In order to achieve the above main object, the two-dimensional weak image measuring device according to the present invention is a two-dimensional weak image measuring device for measuring a two-dimensional image in which photoelectrons generated by incident light from an image to be measured are so weak that they can be resolved in time. A dimensional weak image measuring device, comprising a photocathode, a microchannel plate capable of multiplying photoelectrons from the photocathode to a substantially constant number of electrons for each single photoelectron, and provided opposite to an output surface of the microchannel plate. an image tube consisting of a two-dimensional semiconductor position detector, and output signals from a position signal output electrode of the two-dimensional semiconductor position detector to output a position signal indicating that electrons are incident on the two-dimensional semiconductor position detector. an incident position calculation circuit; an incident amount calculation circuit that adds output signals from position signal output electrodes of the two-dimensional semiconductor position detector to output an amount of electrons incident on the two-dimensional semiconductor position detector; a half-divided circuit that determines from the output of the quantity calculation circuit whether or not the output corresponds to a single photon level and generates a determined output; and when it is determined by the half-divided circuit that the output corresponds to the single photon level; and a two-dimensional counter that adds a unit signal to a counter at an address specified by the output signal of the injection position calculation circuit.

According to the configuration, an image of ultra-weak light can be detected with a high dynamic range.

Furthermore, if an image with an intensity that can be captured by the conventional video camera tube described above is attenuated once and then measured and reconstructed, it can be detected and reconstructed as a high-quality image with a larger dynamic range than the image captured by the conventional device. You can also.

The present invention will be described in more detail below with reference to the drawings and the like.

FIG. 1 is a block diagram showing an embodiment of a two-dimensional weak image measuring device according to the present invention.

The image of the subject 1 is transferred to the image tube 3 by the optical system 2.
formed on the photocathode.

The illuminance of the image formed by the subject 1 on the photocathode of the image tube 3 is low enough to generate 10 ⁴ or less photoelectrons per second from the photocathode of the image tube. Considering the quantum efficiency and the area of the photocathode, this is 1/10 ³ to 1/10 ⁸ of the lower limit illuminance that can be captured by the conventional imaging device described above.

Note that if the subject has higher brightness, it is necessary to reduce the number of incident photons using a density filter with low transmittance so that the illuminance is about the above-mentioned level.

The structure of the image tube 3 used in the apparatus according to the present invention will be explained with reference to FIG.

The photocathode 31 forms a photoelectron source that emits electrons in response to a subject image formed on the photocathode, more precisely, an image of photons incident on the photocathode.

This embodiment uses a photocathode made of alkali metal and antimony. The photocathode 31 is formed on the inner wall surface of an entrance window 30 that constitutes a part of the airtight container 3 . A photoelectron image emitted from the photocathode 31 is focused onto the incident surface of the microchannel plate 33 by the focusing electrode 32 . The microchannel plate 33 has a large number of through holes (channels) connecting from the incident surface to the exit surface, and a secondary electron emitting surface is formed on the inner wall of the through hole. The electrons that have entered the incident surface of the microchannel plate 33 are multiplied while maintaining the information of the incident position and are emitted from the exit surface of the microchannel plate 33. Microchannel plate 33
In order to make the multiplication factor for multiplying one incident photoelectron as close to a constant value as possible, the channel is curved and the channel length is given to be more than 100 times the channel diameter.

The resistance of the dynode wall formed on the inner surface of the channel is increased.

With this configuration, the multiplication factor of a single photoelectron becomes a substantially constant value, and it becomes possible to distinguish between the noise generated from the microchannel plate 33 caused by all single photoelectrons and the noise generated from the inner surface of the channel due to heat. .

The semiconductor position detector 34 is a two-dimensional position detector that outputs a current signal corresponding to the incident position when electrons are incident on its incident surface.

A power source E1 is connected between the focusing electrode 32 and the photocathode 31, a power source E2 is connected between the photocathode 31 and the incident surface of the microchannel plate 33, and a power source E3 is connected between the incident surface and the exit surface of the microchannel plate 33. A power source E4 is connected between the output surface of the semiconductor position detector 33 and the semiconductor position detector 34.

The structure and operation of the semiconductor position detector 34 will be described later together with the structure and operation of the incident position calculation circuit 4 (FIG. 1).

The incident position calculation circuit 4 processes the output signal of the image tube 3 and determines the position of the light incident on the photocathode 31 of the image tube 3 by setting the center point of the semiconductor position detector 34 corresponding to the center of the photocathode as the origin. This is an arithmetic circuit that calculates and outputs a position signal expressed in orthogonal coordinates (hereinafter referred to as X and Y) and a signal related to the amount of electrons incident on the semiconductor position detector 34 (hereinafter referred to as Z).

The pulse height selector 5 has a first threshold value set between the center of the Z output signal caused by a single photoelectron of the incident position calculation circuit 4 and the output due to thermal noise from a microchannel plate, etc. It is a window comparator with a second threshold set between the signal and the output due to inherent noise.

However, in some cases, the second threshold may be omitted and all signals greater than the first threshold may be extracted.

The first address signal generator 6 is composed of an analog-to-digital converter, and outputs a signal specifying each counter address of the two-dimensionally arranged counter 11 from the X and Y signals of the position calculation circuit 4.

Counter 7 counts the output pulses of clock pulse generator 10 and is reset by the vertical and horizontal synchronization signals of synchronization signal generator 17. The count value reset by the vertical synchronization signal changes the Y coordinate to
The counter reset by the horizontal synchronization signal is
Represents coordinates.

The second address signal generator 8 converts the output signal of the counter 7 into a signal specifying the address of the two-dimensional counter 11. First selection gate circuit 20
passes either the output signal of the first address signal generator 6 (write address signal) or the external address signal (read address signal) to the second selection gate circuit 9.

The second selection gate circuit 9 selects either the output signal of the first selection gate circuit 20 or the output signal of the second address signal generator 8 using the output signal of the 1/8 counter 18 and passes the selected signal to the two-dimensional counter 11. .

The two-dimensional memory 111 of the two-dimensional counter 11 is
A large number of counters are formed to correspond to two-dimensional pixels.

The detailed configuration of the two-dimensional counter 11 will be explained with reference to FIG. The two-dimensional counter 11 includes a two-dimensional memory 111 and a buffer memory 112 connected to the data output terminal of the two-dimensional memory 111. The output of the buffer memory 112 is selectively sent to an incrementer 115 or to the outside according to an external command. a third selection gate circuit 114 that sends a signal;
Incrementer 1 that adds 1 to the input signal and sends it out
15, it includes this incrementer 115, an input buffer memory 116 connected to the data input end of the two-dimensional memory 111, and a read/write control circuit 121 that makes the two-dimensional memory 111 ready for reading or writing. ing.

When the output signal of the pulse height selector 5 is input to the first input terminal of the read/write control circuit 121, the two-dimensional counter 11 counters the address specified by the output signal of the first address signal generator. Add 1 (unit signal) to the contents of. This operation will be called counting. Further, the contents of the counter at the address specified by the second address signal generator 8 are read out and used for reading by a television monitor, which will be described later. 2D counter 11
The count value is not reset by reading the contents.

The detailed counting and reading operations will be described later.

12 and 12' are buffer memories, and 13 is a scale controller. The number of digits to shift the output signal of the buffer memory 12 (which is a parallel signal consisting of a plurality of bits) depends on the output of the highest order detector 14. The highest level detector 14 is buffer memory 1
The highest level of "1" among the output signals in the binary signal format of 2 is detected. If the highest level of the output signal of the buffer memory 12, which is "1", is not higher than the already detected level, the output of the highest level detector 14 is held. The scale controller 13 shifts the digits so that the digit indicated by the output signal of the highest detector 14 becomes the most significant output of the scale controller 13, and outputs the data. 15 is a digital to analog converter. A synchronous mixer 19 synthesizes the output of the digital-to-analog converter 15 into a standard television video signal. 16 is a television monitor. Displays the video signal on a cathode ray tube. This operation will be referred to as television reading. Displaying only a certain number from the highest level on the TV monitor in this way eliminates the difficulty in viewing the image due to the small dynamic range of the TV monitor.

FIG. 3 shows a block diagram of the semiconductor position detector 34 and the incident position calculation circuit 4 that calculates the output signal of the semiconductor position detector 34. The semiconductor position detector 34 has a pn junction plane parallel to the surface of the silicon semiconductor, and four electrodes 35, 36, 37, and 38 separated into portions corresponding to the four sides of a rectangle. Here, it is assumed that electrodes 35 and 36 are facing each other, and electrodes 37 and 38 are facing each other. 4 electrodes 3
The electrical resistance between any point 39 on the surface surrounded by points 5, 36, 37, and 38 and each of the electrodes is proportional to the distance therebetween. Therefore, when electrons are incident on the point 39, a current that is inversely proportional to the distance from each electrode to the point 39 is sent out. At this time, electron multiplication occurs in the silicon semiconductor in response to the energy of the incident electrons. 41, 42, 43, and 44 are pulse amplifiers. 45, 46, 47, and 48 are integrators. The timing signal generator 56 is connected to the pulse amplifier 4
The outputs of 3 and 44 are added together and used as a trigger signal to generate a timing signal. This timing signal limits the timing for starting the integration of the integrators 45, 46, 47, and 48 and the integration time. This integration time is, for example, 6 microseconds. This time is determined in accordance with the magnitude of the time constant of the output signal of the semiconductor position detector 34. Further, this time is sufficiently longer than the operation cycle of a two-dimensional counter, which will be described later.

Note that when there is a delay time in timing generation in the circuit shown in FIG. 3, the integration start time will be delayed with respect to the input signal, and there is a possibility that the integration accuracy will deteriorate. In such a case, the pulse amplifier 4
It is necessary to insert a delay circuit between the integrators 1, 42, 43, and 44 and the corresponding integrators 45, 46, 47, and 48, respectively.

In FIG. 3, the current sent out from the electrode 35 is amplified by a pulse amplifier 41, the signal current obtained by integrating it by an integrator 45 is amplified by I35, and the current sent out from the electrode 36 is amplified by a pulse amplifier 42. , the signal current obtained by integrating by the integrator 46 is amplified by the pulse amplifier 43, the current sent from the electrode 37 is amplified by the pulse amplifier 43, and the signal current obtained by integrating by the integrator 47 is
I37, pulse amplifier 44 delivered from electrode 38
The signal current obtained by amplifying the signal and integrating it by the integrator 48 is designated as I38.

The adder 50 receives the output I35 of the integrators 45 and 46.
and I36 are added to output (I35 + I36).

The adder 52 receives the output I37 of the integrators 47 and 48.
and I38 are added to output (I37 + I38).

Adder 55 adds the outputs of the adders 50 and 52 and outputs (I35+I36+I37+I38).

Similarly, the subtracter 49 outputs (I35-I36) and the subtracter 51 outputs (I37-I38).

53 and 54 are dividers, and the output signal X of the divider 53 is given by the following equation.

X=(I35−I36)/(I35+I36) (1) The output signal Y of the divider 54 is given by the following formula.

Y=(I37−I38)/(I37+I38) (2) The output signal Z of the adder 55 is given by the following equation as described above.

Z=(I35+I36+I37+I38) ...(3) The center of the square surrounded by the four electrodes 35, 36, 37, and 38 is the origin, the distance of each electrode from the origin is 1, and the direction from electrodes 36 to 35 is X. By defining the direction from the direction electrodes 38 to 37 as the Y direction, equations (1), (2), and (3) have the following meanings.

(1) Equation: X coordinate (X) of electron incident point 39 (2) Equation: Y coordinate (Y) of electron incident point 39 (3) Equation: Electron incident amount (Z) This will be explained together with the detailed structure.

At the start of the operation, the first selection gate circuit 2
0 connects between the first address signal generator 6 and the second selection gate circuit 9, and connects the third selection gate circuit 114.
connects between the output buffer 112 and the incrementer 115.

When photons are incident on the image tube 3 from the subject 1, photoelectrons are emitted from the photocathode 31 and incident on the microchannel plate 33 with a certain probability, for example, 20%. At this time, the photoelectron position on the photocathode 31 is maintained as a position on the incident surface of the microchannel plate 33. Microchannel plate 3
3, the incident electrons are multiplied and reach the exit surface. The multiplied electrons emitted from the emission surface enter the semiconductor position detector 34. During this time as well, the position of the light incident point on the photocathode 31 is maintained.

Here, the relationship between the Z signal and the threshold value of the pulse height selector 5 will be explained with reference to FIG.

FIG. 4 is a histogram showing the Z signal pulse height on the horizontal axis and the frequency of each output value on the vertical axis. The Z signal pulse appears every time a single photoelectron is generated on the photocathode, and only the output should appear at the same pulse height for every single photoelectron, but in reality, two pulses are generated as shown in Figure 4D. peak p, q
It appears as a distribution with . This curve D is estimated to be given as the sum of the output frequency distribution B caused by thermal noise, the output distribution A caused by a single photoelectron, and the output distribution C when photoelectrons are generated continuously to an inseparable extent. can.

Therefore, in the present invention, the threshold values of the pulse height selector 5 are set at two points L and H in the figure, and only the Z output between them is measured.

The X position signal and Y position signal from the incident position arithmetic circuit 4 are converted into address signals for the two-dimensional counter 11 by the first address signal generator 6, and are converted into address signals for the two-dimensional counter 11 via the selection gate circuit 9. Specify. Since the maximum repetition period of the output of the incident position calculating circuit 4 is longer than the operation cycle of the two-dimensional counter 11, the two-dimensional counter 11 may be inputted when the output of the incident position calculating circuit 4 is generated. The two-dimensional counter 11 has 512×512=262144 counters, in other words, the two-dimensional memory 111 has
Assume that it has 2621144 memory locations. The Z signal from the incident position calculation circuit 4 is input to a wave height selector 5. The wave height selector 5 sends out a trigger signal pulse when the Z signal is between an arbitrarily set lower limit and an upper limit, and the two-dimensional counter 11 changes the contents of the counter at the specified address to 1 when receiving the pulse. Put it in your mouth. In this way, the two-dimensional counter 1
1, only the signal corresponding to one photoelectron can be added, excluding thermal noise and the pulse corresponding to two photoelectrons.

The frequency of the clock pulse is selected so that one clock pulse corresponds to each address of the two-dimensional counter 11, taking into account the retrace period of television scanning. As mentioned above, the address in the X direction can be specified by the value counted by the counter 7 after the frequency of the clock pulse is reset by the horizontal periodic signal.

The address in the Y direction can be reset by the vertical synchronization signal without counting clock pulses, and then
It is sufficient to count the number of horizontal synchronization signals. While the output of the incident position calculation circuit 4 has its origin at the center of the screen, the count output from the counter 7 has its origin at the upper left corner of the screen, and the reading order is an interlaced scanning method. Appropriate amendments must be made to make it compatible. The second address signal generator 8 corrects the count value output from the counter 7 and converts it into an address signal for the two-dimensional counter 11.
The above correction is, for example, 512/2 for the count value in the X direction.
=256, and in the Y direction, the count for one horizontal scan is doubled, and 245 is subtracted in the first field, and 244 is subtracted in the second field.

The second selection gate circuit 9 is controlled by a pulse obtained by dividing the output of a clock pulse generator 10 by a ⅛ counter 18. FIG. 5 shows the waveform sent out from the 1/8 counter 18. This is two-dimensional memory 111
It controls the basic timing (basic cycle) of , and is divided into the first half and the second half as shown in FIG. The first half of one cycle is "1" (high state) and the second half is "0" (low state). This pulse causes the second selection gate circuit 9 to
is used for counting or reading the contents to the outside through the address signal output from the first address signal generator or an external address signal in the first half of one cycle, and is used for counting or reading the contents to the outside through the address signal output from the second address signal generator in the second half. Used to read the contents of the dimensional counter using the television method.

The pulse outputted from the 1/8 counter 18 to the second selection circuit 9 is also outputted to the two-dimensional counter 11,
The wave height selector 5 is connected to the read/write control circuit 121
Only when a trigger signal pulse is sent to the first input terminal 122 of the _T1 in FIG. In the first half of the next basic cycle shown in Figure 5 T ₂ ,
Write to the same address in the two-dimensional memory 111.
The above-mentioned counting is performed by this operation. Fifth
In the latter half of each basic cycle shown in Figures _T3 and _T4 , the memory contents of eight consecutive addresses starting from the designated address are read non-destructively. The stored contents read out by this operation are used for the television reading described above.

The reason for reading out the signals of eight counters at once is as follows. If one counter signal is read out in one cycle, the readout period will be 9.7MHz, taking into account the horizontal and vertical retrace periods. Furthermore, since the data must be read out in the latter half of one cycle, the time given for one readout is 52 nanoseconds. This is impossible or near the time limit with currently available equipment. If eight counters are read at once, the time given for one reading is 416 nanoseconds, which is plenty of time. This reading operation follows the horizontal and vertical synchronization signals sent by the television synchronization signal generator 17. Such an operation is called parallel-to-serial conversion. Also, as mentioned above, the two-dimensional counter 11 has 512 x 512 counters. Therefore, if 512 counters are made to correspond to one horizontal scanning line, even if 8 counters are read at once, one horizontal scanning line will be read out 64 times. can be processed. On the other hand, television has 525 scanning lines, but only 488 are displayed because 6.5% of them correspond to the vertical blanking period.

The output signals of the eight counters read from the two-dimensional counter 11 are temporarily stored in the first buffer memory 12.
8, and the output signals of each counter are read out sequentially. Reading from the first buffer memory 128 is allotted the next cycle, or 816 nanoseconds. In the second half of the cycle in which data is read from the first buffer memory 128, data is read from the two-dimensional counter 11 to the second buffer memory 129. Therefore, two-dimensional counter 1
1 and the input terminals of the first buffer memory 128 and the second buffer memory 129. However, since this is self-evident, the description thereof is omitted in FIG. 1 and this specification. do. The signal output from the first buffer memory 128 or the second buffer memory 129 is input to the scale controller 13 and also to the highest position detector 14. The highest order detector 14 detects which digit is the highest order "1" in the output signal of the buffer.

The highest level detector 14 detects the highest level for all inputs, but the output signal is held unless a signal larger than the previous input is input.

The position controller 13 shifts the input signal according to the output of the highest position detector 14. That is, the digit of the input signal indicating the output of the highest detector 14 is shifted so that it always becomes the same digit in the output signal.

The output of the position controller 13 is converted into an analog signal by a digital-to-analog converter 15, and then mixed by a synchronization mixer with the horizontal and vertical synchronization signals sent out from the television synchronization signal generator 17. The signal is input to the digital monitor 16 as a video signal.

Here, when the observer recognizes that the image displayed on the television monitor 16 is good due to the sufficient number of photons, the observer selects the first selection gate by an external address selection signal by manual operation. The first selection gate circuit 20 that operates the circuit 20 is
Open the gate between the external address generator (not shown) and the second selection gate circuit 9. At the same time, the two-dimensional counter 11 receives the third external address selection signal.
It is input to the second input terminal 123 of the selection gate circuit 114 and the read/write control circuit 121. At this time, the first half of the basic cycle shown by T ₁ T ₂ in FIG. 5 is always in the read mode. Output buffer 112
and an external display device (not shown) opens, output buffer 112 and incrementer 1
The gate between 15 closes. Furthermore, the memory 111 enters the read mode in the first half of the basic cycle.

At the same time, an arbitrary address signal is sent to the first selection gate circuit 20 from the external address generator.

Through this operation, the image signal stored in the two-dimensional memory 111 of the two-dimensional counter 11 is read out from the two-dimensional counter 11 as a digital signal to an external display device and an external storage device through the third selection gate circuit 114. be able to.

At this time, the contents of the two-dimensional memory 111 are not changed by reading.

An example of an external display device is a printer, and an example of an external storage device is magnetic tape.

The addresses for this readout may be in the same order as the readout for television display described above. Alternatively, only a specific part of the image may be used.

For example, the reading speed uses two cycles of a 9.7 MHz clock pulse. 1 for each read
Only one counter is read. These can be fully understood from the configuration and operation of this embodiment described above.

Since the present invention is configured and operates as described above, it has the following effects.

By setting a lower limit on the wave height of the detection pulse and an image tube with a microchannel plate and a two-dimensional semiconductor position detector that multiply a single photoelectron to a number of electrons close to a certain value, photoelectrons can be generated by generating one photoelectron. A quadratic image can be measured by detecting the incident position of photons on the surface and removing noise components due to thermal noise.

Furthermore, since this is counted in terms of addresses using a two-dimensional counter, extremely weak optical images can be observed with a large dynamic range. In this embodiment, a dynamic range of 6×10 ⁴ is obtained by making each address of the two-dimensional counter 16 bits.

Furthermore, in detecting pulses of the Z signal, setting an upper limit on the wave height may indicate an incorrect position. The output (signal-specific noise) caused by two simultaneously incident photoelectrons is removed, making it possible to detect an optical image more accurately.

By displaying the output of the two-dimensional counter on television, the image being formed can be observed in real time, and the optimal timing for reading image information can be determined.

Various modifications can be made to the embodiments described in detail above within the scope of the present invention.

It can be used not only to measure weak images using visible light, but also to measure invisible light weak images using infrared rays, ultraviolet rays, X images, and gamma rays. Therefore, in the present invention, the photocathode should be interpreted in a broad sense, even though it means converting the energy of electromagnetic radiation into electrons. These measurements can be easily carried out by changing the properties of the entrance window and photocathode of the above-mentioned embodiment device to be suitable for each electromagnetic radiation.

A gallium arsenide photocathode is suitable for measuring weak images using infrared rays.

For the measurement of weak images using ultraviolet light, a thin plate of lithium fluoride is suitable for the gallium iodide photocathode and the entrance window.

For the measurement of invisible light weak images using X-rays and gamma rays, a thin gold plate is suitable for the photocathode, and a thin plate of beryllium or aluminum is suitable for the entrance window.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of a two-dimensional weak image measuring device according to the present invention, Fig. 2 is a schematic diagram showing the structure of an image tube, and Fig. 3 shows a semiconductor position detector and a position calculation circuit in detail. Block diagram, No. 4
The figure is a histogram showing the distribution of Z output of the incident position calculation circuit, and Figure 5 is from the clock pulse generator.
A waveform diagram showing pulses sent to the 1/8 counter,
FIG. 6 is a block diagram showing the detailed configuration of the two-dimensional counter. 1... Subject, 2... Optical system, 3... Image tube, 31... Photocathode, 32... Focusing electrode, 33...
... Microchannel plate, 34 ... Semiconductor position detector, 4 ... Incident position calculation circuit, 41, 4
2, 43, 44...pulse multiplier, 45, 46,
47, 48... Integrator, 49, 51... Subtractor,
50, 52, 55... Adder, 53, 54... Divider, 5... Pulse height selector, 56... Timing signal generator, 6... First address signal generator, 7... Counter, 8... Second address signal generator, 9... Second selection gate circuit, 10... Clock pulse generator, 11... Two-dimensional counter, 11
DESCRIPTION OF SYMBOLS 1... Two-dimensional memory, 112... Buffer memory, 114... Selection gate circuit, 115... Incrementer, 116... Buffer memory, 12
8,129... Buffer memory, 13... Scale control device, 14... Highest level detector, 15... Digital analog converter, 16... Television monitor, 17... Synchronization signal generator, 18... 1 /8 counter, 19... synchronous mixer, 20... first selection gate circuit, 21... gate circuit.

Claims (1)

[Claims] 1. Two-dimensional weak image measurement for measuring a two-dimensional image in which photoelectrons generated by the photocathode are weak enough to be time-resolved by receiving incident light from an image to be measured on a photocathode. A device comprising a photocathode, a microchannel plate capable of multiplying photoelectrons from the photocathode to a substantially constant number of electrons for each single photoelectron, and a two-dimensional semiconductor provided opposite to an exit surface of the microchannel plate. an image tube comprising a position detector; and an incident position calculation circuit that calculates output signals from a position signal output electrode of the two-dimensional semiconductor position detector and outputs a position signal indicating that electrons are incident on the two-dimensional semiconductor position detector. and an incident amount calculation circuit that adds output signals from the position signal output electrodes of the two-dimensional semiconductor position detector and outputs the amount of electrons incident on the two-dimensional semiconductor position detector; a pulse height selector that determines from the output whether the output corresponds to a single photoelectron level and generates a determined output; and when the pulse height selector determines that the output corresponds to a single photoelectron level, the input A two-dimensional weak image measuring device comprising a two-dimensional counter that adds a unit signal to a counter at an address specified by an output signal of a position calculation circuit. 2 The pulse height separator is a first pulse height selector for separating low-level thermal noise output from output caused by a single photoelectron.
A two-dimensional weak image measuring device according to claim 1, having a threshold value of . 3. Claim 2, wherein the pulse height selector further comprises a second threshold for separating signal-specific noise caused by simultaneous generation of two or more photoelectrons from output caused by a single photoelectron. The two-dimensional weak image measuring device described. 4 A two-dimensional weak image measuring device for measuring a two-dimensional image in which photoelectrons generated by the photocathode are weak enough to be time-resolved by receiving incident light from an image to be measured on a photocathode, An image consisting of a surface, a microchannel plate capable of multiplying photoelectrons from the photocathode to a substantially constant number of electrons for each single photoelectron, and a two-dimensional semiconductor position detector provided opposite to the exit surface of the microchannel plate. a tube, an incident position calculation circuit that calculates an output signal from a position signal output electrode of the two-dimensional semiconductor position detector and outputs a position signal that electrons are incident on the two-dimensional semiconductor position detector, and the two-dimensional semiconductor an incident amount calculation circuit that adds output signals from position signal output electrodes of the position detector and outputs the amount of electrons incident on the two-dimensional semiconductor position detector; a pulse height selector that determines whether or not it corresponds to a single photoelectron level and generates a discrimination output; and an output signal of the incident position calculation circuit when the pulse height selector determines that it corresponds to a single photoelectron level; A two-dimensional weak image measuring device comprising: a two-dimensional counter that adds a unit signal to a counter at an address specified by the two-dimensional counter; and an output device that outputs the contents of the two-dimensional counter. 5 The pulse height separator is a first pulse height selector for separating low level thermal noise output from output caused by a single photoelectron.
A two-dimensional weak image measuring device according to claim 4, having a threshold value of . 6. Claim 5, wherein the pulse height selector further comprises a second threshold for separating signal-specific noise caused by simultaneous generation of two or more photoelectrons from output caused by a single photoelectron. The two-dimensional weak image measuring device described. 7. The two-dimensional weak image measuring device according to claim 4, wherein the output device is a television monitor device and is configured to display the contents of the two-dimensional counter during measurement in real time. 8. The two-dimensional weak image measuring device according to claim 7, wherein the output device further includes a printer device that outputs the contents of the two-dimensional counter as numerical data. 9. The two-dimensional weak image measuring device according to claim 7, wherein the output device is a magnetic tape device that externally stores the contents of the two-dimensional counter.