JPS6334403B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is for measuring two-dimensional weak images in which the input of a single particle such as a single photon, which is the basis of image composition, is within a two-dimensional resolution unit and is below the level that can be resolved in time. This invention relates to a two-dimensional weak image measuring device.

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

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, the image pickup tube using the above-mentioned target essentially has a small dynamic range, and even those with a relatively large dynamic range do not exceed 10 ³ .

In order to measure images with lower illuminance that cannot be captured with the above-mentioned device while maintaining a satisfactory contrast, the inventors of the present invention determined that the incident location of photons is determined 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 the number of photoelectrons and counting the frequency at which photoelectrons are generated from each generation position. When attempting 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 three 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 separated, 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-resolved failure is extremely low.

The third problem is how to obtain the desired optimal measurements, especially when the contrast between light and dark in the image is large.

Generally speaking, in order to measure dark areas, it is necessary to carry out measurements over a long period of time. In that case, more measurements will be taken than necessary for bright areas.

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 output of the microchannel plate due to two or more photoelectrons is incident on the semiconductor position detection device simultaneously or at an interval that cannot be resolved in time, the output of the semiconductor position detection device is larger than that in the case of a single photoelectron. Become. 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 third problem was solved by converting the brightness of pixels into the time required to obtain a constant input.

The main object of the present invention is to produce a two-dimensional image in which the input of a single particle such as a single photon is so weak that it can be time-resolved within a two-dimensional resolution unit, for example, at the lower limit of what can be captured by the aforementioned television imaging device. An object of the present invention is to provide a two-dimensional weak image measuring device that can measure a two-dimensional weak image with a desired quality while maintaining good contrast on a two-dimensional weak image with an illuminance of 200 nm or less.

In order to achieve the above main object, the two-dimensional weak image measuring device according to the present invention is such that the incidence frequency of the particle beam caused by the image, which is incident on the two-dimensional semiconductor position detector, is so weak that it can be resolved in time. A two-dimensional weak image measuring device for measuring a two-dimensional image, which calculates an output signal from a position signal output electrode of the two-dimensional semiconductor position detector, and calculates the output signal of the two-dimensional particle that is the cause of the output signal. an incident position calculation circuit that outputs an address signal indicating the position of incidence on the semiconductor position detector; and an input position calculation circuit that calculates an output signal from the position signal output electrode of the two-dimensional semiconductor position detector to output the signal to the two-dimensional semiconductor position detector. an incident amount calculation circuit that outputs the amount of incident particles; a pulse height selector that determines from the output of the incident amount calculation circuit whether or not the output corresponds to a single particle level and generates a discrimination output; A memory formed from a group of counters corresponding to the address of the two-dimensional semiconductor position detector, and a memory formed from a group of counters corresponding to the address of the two-dimensional semiconductor position detector, and a memory of the address specified by the incident position calculation circuit when it is determined by the pulse height selector that it corresponds to a single particle level. Add a unit signal to the counter, monitor the contents of the counter in the memory, and when the count value of any counter reaches a preset value, store the time until reaching the preset value in the counter at that address. It consists of a memory control circuit and an output device that outputs the contents of the memory.

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 in which a two-dimensional weak image measuring device according to the present invention is used for measuring weak light.

The image of the subject 1 is transferred to the image tube 3 by the optical system 2.
is 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, the illuminance is 10 ^-3 to ^{10 -8} , which is the lower limit illuminance that can be captured by the conventional imaging device mentioned 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 the signal from the microchannel plate 33 caused by all single photoelectrons from 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.

FIG. 3 shows a block diagram of the semiconductor position detector 34 and the incident amount and incident position calculation circuit 4 for calculating the output signal of the semiconductor position detector 34.

The semiconductor position detector 34 has a p-n junction plane parallel to the surface of the silicon semiconductor, and four electrodes 35, 36, 3 electrically separated into parts corresponding to the four sides of a rectangle.
7 and 38 are formed. Here electrodes 35 and 3
6 are facing each other, and electrodes 37 and 38 are facing each other. The electrical resistance between any point 39 on the surface surrounded by the four electrodes 35, 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 whose distance from each electrode to the point 39 is inversely proportional is sent out.
At this time, electron multiplication occurs within 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 adds the outputs of the pulse amplifiers 43 and 44, uses this as a trigger signal, and generates 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. Also during this time,
This 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, it is necessary to insert a delay circuit between the pulse amplifiers 41, 42, 43, 44 and the corresponding integrators 45, 46, 47, 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 is amplified by a current pulse amplifier 44 sent from an electrode 38, and integrated by an integrator 48 to obtain a signal current 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 electrode 36 to 35 is By defining the direction from the X-direction electrodes 38 to 37 as the Y direction, equations (1), (2), and (3) each have the following meanings.

Equation (1): X coordinate (X) of the electron incident point 39 (2) Equation: Y coordinate (Y) of the electron incident point 39 (3) Equation: Amount of electron incident (Z) In this way, the incident position calculation circuit 4 processes the output signal of the image tube 3 and calculates the position of the light incident on the photocathode 31 of the image tube 3 in orthogonal coordinates with the origin at the center point of the semiconductor position detector 34 corresponding to the center of the photocathode. This is a calculation circuit that calculates and outputs the position signals (hereinafter referred to as X and Y) and 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.

Next, referring to FIG. 4, the Z signal and wave height selector 5
Explain the relationship between the threshold values.

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. A Z signal pulse appears every time a single photoelectron is generated on the photocathode, and only an output with the same pulse height should appear 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 of the pulse height selector 5 is set at two points L and H in the figure, and only the Z output between them is the subject of measurement, and only when such Z output is input. A signal is sent to an incrementer 7, which will be described later.

The memory 6 is a random access memory formed from a group of counters corresponding to the addresses of the two-dimensional semiconductor position detector 39.

In this embodiment, the memory 6 has 512×512=262144 counters or 262144 storage locations.

A corresponding address is specified by the output signal of the injection position calculation circuit 4, and the contents of the counter at that address are called into the incrementer 7.

The incrementer 7 adds 1 to the above content on the condition that the signal from the wave height selector 5 is received. The added contents are returned to the original counter in the memory 6. However, the counting time converter 9 described later
When the contents of the counter have already been converted into time data, the addition is not performed.

When the content read from the memory 6 reaches a certain number (for example, 32768), the counting time converter 9 converts it into data of the time from the start of measurement to that point and returns it to the original address.

The count value time value discriminator 9 determines whether the content read from the memory 6 is data that has already been converted into time data or a count value, and then passes the count value time value discriminator 9 to the incrementer 7 and the count value time value discriminator 9. Sends a 9th grade discrimination signal. Based on the determination signal, the incrementer 7 increments the content by 1 if the content being called is a counter value, and returns it to the memory 6 as is if it has been converted to time data.

One bit of the time data stored in each counter in the memory 6 is used as a flag, and is used for the above-mentioned determination.

The monitor 10 is a cathode ray tube display and sequentially reads and displays the contents of the memory 6. It is possible to select one of a mode in which the count value of the counter is converted into a luminance signal and displayed, a mode in which time data is displayed at a specific luminance, and a mode in which both are displayed simultaneously. This allows the measurer to know in real time how much time data has been converted.

The output device 11 is a device that hard copies the contents of the memory 6 after the measurement is completed. Since all the information regarding the image has already been recorded in the memory 6, it is output in any of the following modes.

There is a mode in which the data itself is converted into time by the printer, a mode in which the count value itself is output, and a mode in which each is converted into intensity and output as an image by the halftone printer.

The control device 12 is a device that generates control timing for the entire device, and generates startup control, readout control to the monitor 10, and control signals for the output device 11.

The operation of the device according to the above configuration will be explained.

The upper limit value of the counter in the memory 6 and the threshold value of the wave height selector 5 are set and the device is activated.

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 position on the photocathode 31 from which the photoelectrons are emitted is maintained as the position on the incident surface of the microchannel plate 33. The incident electrons are multiplied by the microchannel plate 33 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.

The contents of the counter at the corresponding address in the memory 6 are read by the incrementer 7 in response to the X position signal and the Y position signal from the incident position calculation circuit 4.

The Z signal of the incident position calculation circuit 4 is input to the pulse height selector 5, and the pulse height selector 5 sends a trigger signal pulse to the incrementer 7 when the Z signal is between an arbitrarily set lower limit and an upper limit. Ru.

When the incrementer 7 receives the trigger signal pulse, it adds 1 to the contents of the counter and returns the counter to the original value.

When there is no trigger signal pulse from the wave height selector 5, the signal that caused the address generation is caused by the simultaneous incidence of two or more photoelectrons or other noise, so the contents of the counter do not change. Return the counter to the original address without adding 1.

The status of the addition is monitored by the numerical time value discriminator 8, and the addition is not performed if the count value has reached the count value set before startup and has already been converted into time data by the counting time converter 9.

Monitor 10 by reading and writing addresses specified by position calculation circuit 4 and sequential scanning
Reading is performed on a time-division basis, and the measurement status is displayed on the monitor 10 in real time.

While observing the screen of the monitor 10, the measurer can grasp the proportion of the portion converted into time data at intervals. The measurement is terminated when the desired ratio is reached, the content of the measurement is outputted by the output device 11, and the measurement is terminated. It is also possible to set the desired ratio in advance to 50% of the previous pixel, count the converted output of one frame, and automatically end the measurement.

As explained above, the measuring device according to the present invention has a microchannel plate that multiplies a single photoelectron to a number of electrons close to a constant value, an image tube that has a two-dimensional semiconductor position detector, and a lower limit on the wave height of the detection pulse. By providing this, it is possible to detect the incident position of a photon on the photocathode by generating one photoelectron, remove noise components due to thermal noise, and measure a two-dimensional image.

The measuring device according to the present invention counts the number of times an incident particle is incident, and when a predetermined number of times is reached, converts it into time data and uses it as the incident intensity at that address.
Image analysis that is different from conventional methods becomes possible.

If the part used for counting the counter in the memory 6 is made 32 bits, a dynamic range of 4×10 ⁹ can be expected.

Since the contents of the memory 6 can be observed in real time on the monitor 10 and the optimal timing for reading image information can be determined, it has become easier to collect necessary data.

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

The two-dimensional semiconductor position detection device described above can provide position-related information even when not only the photoelectrons but also other charged particles and neutrons are incident, so it is possible to It can also be applied to image measurement.

Furthermore, although the above embodiment relates to the measurement of weak images using visible light, infrared rays, ultraviolet rays, X-rays,
It can also be used to measure invisible light weak images using 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 the drawing]

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. 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. 1... Subject, 2... Optical system, 3... Image tube, 31... Photocathode, 32... Focusing electrode, 33...
... Microchannel plate, 34 ... Semiconductor position detector, 4 ... Incident amount and position calculation circuit,
41, 42, 43, 44...Pulse multiplier, 4
5, 46, 47, 48... Integrator, 49, 51...
...Subtractor, 50, 52, 55...Adder, 53,
54...Divider, 5...Pulse height selector, 6...
...Memory, 7...Incrementer, 8...Count value time value discriminator, 9...Count time converter, 10...
Monitor, 11...output device, 12...control device.

Claims (1)

[Claims] 1. Two-dimensional weak image measurement for measuring a two-dimensional image in which the incidence frequency of a particle beam incident on a two-dimensional semiconductor position detector is weak enough to be time-resolved due to the image. A device, which calculates an output signal from a position signal output electrode of the two-dimensional semiconductor position detector and generates an address signal indicating the incident position of the particle that caused the output signal to the two-dimensional semiconductor position detector. an incident position calculation circuit that outputs, and an incidence amount calculation circuit that calculates an output signal from a position signal output electrode of the two-dimensional semiconductor position detector and outputs the amount of particles incident on the two-dimensional semiconductor position detector; a pulse height selector that determines whether the output of the incident amount calculation circuit corresponds to a single particle level and generates a determined output; and a counter that corresponds to the address of the two-dimensional semiconductor position detector. When determined by the pulse height selector to correspond to a single particle level, the incident position calculation circuit adds a unit signal to the counter at the specified address, and adds the unit signal to the counter at the specified address. A memory control circuit that monitors the contents and, when the count value of an arbitrary counter reaches a preset value, stores the time until the preset value is reached in the counter at that address, and an output device that outputs the memory contents. A two-dimensional weak image measurement device consisting of. 2. The memory control circuit adds 1 to the contents of the counter called by the address designation from the injection position calculation circuit, on the condition that a signal is supplied from the pulse height selector, and returns the original value. An incrementer returns the address counter, and when the contents of the counter called by the address specification from the injection position calculation circuit reach a preset count number, it is converted to time data from the start of measurement and returned to the original value. A count time converter returns the counter to the address, and determines whether the contents of the counter called by the address specification from the injection position calculation circuit are converted to time data or counted values, and converted to time data. 2. The two-dimensional weak image measuring device according to claim 1, further comprising a count value/time value discriminator which prohibits addition of said incrementer when the incrementer is incremented. 3 The two-dimensional image, which is caused by the image and which is incident on the two-dimensional semiconductor position detector and whose incident frequency is weak enough to be time-resolvable, is a photocathode, which converts photoelectrons from the photocathode into single photoelectrons. formed on the two-dimensional semiconductor position detector of the image tube, which consists of a microchannel plate that multiplies the number of electrons to a substantially constant value each time, and a two-dimensional semiconductor position detector provided opposite to the exit surface of the microchannel plate. A two-dimensional weak image measuring device according to claim 1. 4 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 3, having a threshold value of . 5. 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. 6. Claim 1, wherein the output device is a hard copy output device that outputs data related to time stored in a counter in a memory after measurement is completed.
The two-dimensional weak image measuring device described in 2. 7. The two-dimensional weak image measuring device according to claim 6, wherein the output device further comprises a television monitor that displays changes in the contents of the counter in the memory.