JP2000275101A - Apparatus and method for measuring light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus for measuring for a long time a light capable of measuring 'when and how many photons' come. SOLUTION: The apparatus 10 for measuring light comprises a photon detector 12 for detecting incident photon, a time signal output unit 14 for outputting a time signal, and a storage unit 16 for storing the time signal output from the unit 14 when the photon has been detected by the detector 12. The detector 12 has an HPD 24 having a photoelectric surface 24a and an APD 24b, a TZ amplifier 26, a peak holding circuit 28, and an A-D converter 30. The unit 14 has a timer 32 and a counter 34. The unit 16 has a comparator 36 and a memory 38. When the photon is incident on the HPD 24, a trigger signal is output from the comparator 36, and number of the photons output from the converter 30 and time information output from the counter 34 are stored in the memory 38.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical measurement device and an optical measurement method, and more particularly to an optical measurement device and an optical measurement method for detecting photons.

[0002]

2. Description of the Related Art With the development of optical technology in recent years, light is used in various fields such as optical communication, optical sensing, and optical computers, and it is doubtful that the field of application will be further expanded in the future. There is no room. In such a situation,
"Measuring light" is extremely important.
As a tool for "measuring light", for example, a photomultiplier tube is widely known. According to such a photomultiplier, even weak light can be efficiently detected by the photomultiplier effect.

[0003]

However, in expanding a new field of use of light in the future, it is necessary to measure light at the photon level in time and space, such as "when and how many photons came". It is extremely important. In contrast,
Conventional tools (methods) for "measuring light" including the photomultiplier tube are not tools for measuring light at the photon level in space and time.

On the other hand, in order to measure light at the photon level in space and time, for example, a method of observing the output from an avalanche photodiode capable of detecting light at the photon level with a digital oscilloscope is conceivable. However, since it is not for detecting photons, there is a problem in that it has an unnecessarily high resolution and the time width in which measurement can be performed is extremely limited.

Therefore, the present invention solves the above problems,
"When did photons come?" Or "How many photons came?"
It is an object of the present invention to provide an optical measurement device and an optical measurement method that can measure the distance over a long period of time.

[0006]

In order to solve the above-mentioned problems, an optical measuring device according to the present invention comprises a photon detecting means for detecting an incident photon, a time signal outputting means for outputting a time signal, and a photon detecting means. Storage means for storing a time signal output from the time signal output means when a photon is detected by the control means.

When a photon is detected by the photon detection means, the time signal output from the time signal output means is stored, so that "when the photon came" can be measured. On the other hand, when no photons are detected by the photon detection means, no information is stored in the storage means, and the amount of data stored in the storage means is extremely small.

In the optical measuring apparatus according to the present invention, the photon detecting means detects the number of incident photons, and the storing means detects the photons detected by the photon detecting means when the photons are detected by the photon detecting means. And the time signal output from the time signal output means may be stored.

When a photon is detected by the photon detecting means, the number of photons detected by the photon detecting means and the time signal output from the time signal output means are stored.
"When and how many photons came" can be measured. On the other hand, when no photons are detected by the photon detection means, no information is stored by the storage means, so that the amount of stored data is extremely small.

Further, in the optical measuring device of the present invention, the photon detecting means has an A / D converter, and the A / D converter is
The number of incident photons may be output as a digital value.

By outputting the number of incident photons as a digital value, the signal output from the photon detecting means can be directly
It can be stored by storage means.

Further, in the optical measuring device of the present invention, the photon detecting means includes: a photocathode for emitting photoelectrons according to the number of incident photons; an accelerating means for accelerating the photoelectrons emitted from the photocathode; It is preferable that the semiconductor device further includes a semiconductor photodetector that makes photoelectrons accelerated by the means incident thereon and outputs an output signal corresponding to the number of photoelectrons.

The number of photons incident simultaneously (or at a very close timing) can be efficiently detected by using the photon detecting means provided with the photocathode, the accelerating means and the semiconductor photodetector.

[0014] In the optical measuring apparatus of the present invention, it is preferable that the semiconductor photodetector is an avalanche photodiode.

According to another aspect of the present invention, there is provided a photometric method comprising: a photon detecting step for detecting an incident photon; a time signal outputting step for outputting a time signal; and a photon detecting step. And a storing step of storing the time signal output in the time signal output step.

By storing the time signal output in the time signal output step when a photon is detected in the photon detection step, "when the photon has come" can be measured. On the other hand, when no photons are detected in the photon detection step, no information is stored in the storage step,
The amount of data stored is extremely small.

Further, in the optical measurement method of the present invention, the photon detecting step separates and detects a plurality of incident photons, and the storing step includes the steps of: detecting a photon in the photon detecting step; And storing the number of photons detected by the time signal and the time signal output in the time signal output step.

By storing the number of photons detected in the photon detection step and the time signal output in the time signal output step when a photon is detected in the photon detection step, "when and how many photons came" Can be measured. On the other hand, when no photons are detected in the photon detection step, no information is stored in the storage step, and thus the amount of stored data is extremely small.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical measuring device according to a first embodiment of the present invention will be described with reference to the drawings. First, the configuration of the optical measurement device according to the present embodiment will be described. FIG. 1 is a configuration diagram of an optical measurement device according to the present embodiment.

The light measuring device 10 according to the present embodiment includes a photon detector 12 (photon detector) for detecting an incident photon, a time signal output unit 14 (time signal output unit) for outputting a time signal, and a photon detector. A storage unit 16 (storage means) for storing a time signal output from the time signal output unit 14 when a photon is detected by the unit 12, a CPU 18 for controlling the entire apparatus, an external memory 20 for storing set values and the like, and a measurement result And the like. Hereinafter, each component will be described in detail.

The photon detector 12 includes a hybrid photodetector (hereinafter referred to as HPD 24), a transimpedance amplifier (hereinafter referred to as TZ amplifier 26), a peak hold circuit 28, and an A / D converter 30.

The HPD 24 is an avalanche photodiode (avalanche photodiode) which is a semiconductor photodetector which outputs a photocathode 24a for emitting photoelectrons corresponding to the number of incident photons and an output signal corresponding to the number of photoelectrons emitted from the photocathode 24a. Hereinafter, A
PD 24b) in the vacuum housing 24c. Here, a negative high voltage (for example, −
8 kV) is applied and the anode of the APD 24b is
A reverse bias voltage (for example, +150 V) is applied between the cathodes by a bias circuit 24e. Also,
The HPD 24 is provided with an electronic lens unit (not shown), and efficiently converts photoelectrons emitted from the photocathode 24a to A.
The light can be incident on the PD 24b.

When photons enter the photocathode 24a, photoelectrons corresponding to the number of incident photons are emitted from the photocathode 24a. The photoelectrons are accelerated by the action of the electric field, converged by the action of the electron lens, and enter the APD 24b. When the photoelectrons incident on the APD 24b lose their energy, they generate a large number of hole-electron pairs, and this becomes the first-stage multiplication factor. The first stage multiplication factor depends on the electron acceleration voltage (voltage applied to the photocathode), and the voltage is −8.
It becomes about 1200 in the case of kV. Thereafter, the electrons are further avalanche-multiplied by about 50 times. As a result, APD
A gain of about 60000 times is obtained for the entire 24b. Here, since the multiplication factor of the first stage is as large as about 1200, the multiplication fluctuation of the HPD 24 using the APD 24b is extremely small. Therefore, by using HPD24,
As can be seen from the output wave height distribution diagram for the multiphoton shown in FIG. 2, it is possible to distinguish and detect the number of incident photons. Here, FIG.
The measurement results were obtained by using a preamplifier of Model No. 142A manufactured by Oltech Co., with the applied voltage of a set to −8 kV and the reverse bias voltage of the APD 24b set to +150 V. Also, HPD2
Considering that the gain of No. 4 is about 60000 and the full width at half maximum (FWHM) of the output waveform corresponding to one electron from HPD 24 is about 2 ns, the peak value of the current output from HPD 24 is one photon. 5 μA per unit (for simplicity, the photo-electron conversion efficiency is 100%).

The TZ amplifier 26 is connected to the APD 2 of the HPD 24.
This is a current-to-voltage conversion circuit that amplifies the current signal output from 4b, converts it into a voltage, and outputs it. Such T
The Z amplifier 26 preferably has an amplification factor of amplifying 1 μA to about 50 mV and has a band of about 300 MHz. For example, AU-1494-3 manufactured by Miteq Corporation
00 (product name) or the like is preferable. Here, the peak value of the voltage output from the TZ amplifier 26 is about 0.25 V per photon due to the amplification factor.

The peak hold circuit 28 includes a TZ amplifier 2
6 is output while holding the peak value of the output signal for a certain period. The peak value output from the peak hold circuit 28 is reset by receiving a reset signal from the time signal output unit 14.

The A / D converter 30 receives the trigger signal from the storage unit 16 and A / D converts the signal output from the peak hold circuit 28 and outputs it. At this time, the resolution is adjusted so that the number of incident photons is output as a digital value. More specifically, the input range (0 to 1
V) is divided into four gradations, and the input voltage is from 0.125 V to 0.
In the case of 375V, the digital value is "1" and the input voltage is 0.3
A digital value "2" is output when the input voltage is 75V to 0.625V, a digital value "3" is output when the input voltage is 0.625V to 0.875V, and a digital value "4" is output when the input voltage is 0.875V or more. I do. By adjusting the resolution in this way, the digital value “1” when one photon enters the HPD 24 and the digital value when two photons enter ”
When 2 "and 3 photons enter, the digital value is" 3 ",
When four photons enter, the digital value “4” is output from the A / D converter 30.

The time signal output section 14 includes a timer 32 and a counter 34. The timer 32 generates and outputs a pulse signal at regular intervals (for example, every 5 ns).
The counter 34 receives a pulse signal from the timer 32 and outputs a reset signal to the peak hold circuit 28 at regular intervals (for example, 5 ns). The counter 34 counts the pulse signal received from the timer 32 and outputs a value obtained by multiplying the count value by a period (for example, 5 ns) of the pulse signal to the storage unit 16 as a time signal. Here, the cycle of the pulse signal generated by the timer 32 is preferably set as short as possible to improve the accuracy in terms of determining the time resolution of the optical measurement device 10.
It is preferable to make the time width larger than the time width of the response waveform of one photon output from the photon. This is because if the cycle of the pulse signal is shorter than the response waveform of one photon, one photon may be measured several times. Also, the counter 34
It is reset by a reset signal from the CPU 18 at the start of measurement or the like.

The storage section 16 includes a comparator 36 and a memory 38. The output signal from the peak hold circuit 28 is input to the + input terminal of the comparator 36,
The reference voltage is input to the side input terminal. Here, the reference voltage is 1 at the output of the peak hold circuit 28.
0.13 lower than the voltage (0.25 V) corresponding to photons
V is set. The output of the comparator 36 is output to the A / D converter 30 and the memory 38 as a trigger signal.

The memory 38 stores the output signal output from the A / D converter 30 and the time signal output from the counter 34 at the timing when the trigger signal is received from the comparator 36.

The operation of the storage unit 16 having the above configuration is as follows. That is, while no photon is incident on the HPD 24, no trigger signal is output from the comparator 36, so that data is not stored in the memory 38. On the other hand, when a photon enters the HPD 24, the comparator 3
6 outputs a trigger signal to the A / D converter 30 and the memory 38. In this case, the number of photons is output as a digital value from the A / D converter 30 and stored in the memory 38, and the time signal output from the counter is also stored in the memory 38.

Next, the operation of the optical measurement device according to the present embodiment will be described, and the optical measurement method of the present invention will be described. FIG. 3 is a timing chart showing the operation of the optical measurement device according to the present embodiment. Here, as shown in FIG. 3 (a), two minutes after the measurement start time (t = 0)
Two photons after 8 ns, one photon after 57 ns, 88
One photon after ns, three photons after 103 ns
Consider the case where the light enters D24. When the measurement is started, first, a reset signal is output from the CPU 18 to the counter 34, and the counter 34 is reset. Further, with the reset of the counter 34, counting of the pulse signal received from the timer 32 is started.

Here, until a photon is detected by the HPD 24, that is, until 28 ns after the start of measurement,
Since the output of the HPD 24 and the output of the TZ amplifier 26 are small and the output of the peak hold circuit 28 does not exceed the reference voltage, no trigger signal is output from the comparator 36 and the memory 3
8 is not stored.

On the other hand, 28 ns from the measurement start time
Later, when two photons enter the HPD 24, the photocathode 2
Photoelectrons are emitted from 4a, and electron multiplication is performed by APD 24b. The current output from the HPD 24 is T
The voltage is converted into a voltage by the Z amplifier 26, and a voltage of about 0.5 V corresponding to two photons is output as shown in FIG.

The output signal from the TZ amplifier 26 is output to the A / D converter 30 and the comparator 36 while the peak value is held by the peak hold circuit 28 for a certain period.
Here, since the voltage of 0.5 V is higher than the reference voltage (0.13 V) input to the comparator 36, the voltage of the comparator 3
6 outputs a trigger signal to the A / D converter 30 and the memory 38.

When a trigger signal is input from the comparator 36 to the A / D converter 30, the input signal is A / D converted by the A / D converter 30. Specifically, 2 as an input signal
Since 0.5 V corresponding to a photon is input, FIG.
As shown in the figure, the A / D converter 30 outputs a digital value "
2 "is output.

Further, since the trigger signal is input from the comparator 36 to the memory 38, the output value from the A / D converter 30 and the time signal output from the counter 34 as shown in FIG. Stored in the memory 38.

On the other hand, as shown in FIG. 3C, a reset signal is output from the counter 34 to the peak hold circuit 28 at regular intervals (for example, 5 ns). Accordingly, the output signal of the peak hold circuit 28 is as shown in FIG.
As shown in (1), it is reset at regular intervals (for example, 5 ns).

Similarly, when photons enter the HPD 24, the number of incident photons and the time signal at that time are stored in the memory 38. As a result, the data stored in the memory 38 is as shown in FIG. become that way.

Next, the operation and effects of the optical measurement device according to the present embodiment will be described. When the photon is detected by the HPD 24, the optical measurement device 10 according to the present embodiment stores the number of photons detected by the HPD 24 and the time signal output from the counter 34 in the memory 38, thereby “when the photon is detected. , How many came? " On the other hand, when no photons are detected by the HPD 24, no information is stored in the memory 38, and the amount of data stored is extremely small. Therefore, the capacity of the memory 38 can be effectively used, and “when and how many photons have arrived” can be measured for a long time.

More specifically, for example, when photons enter with a time-series distribution as shown in FIG. 4A, it is attempted to measure when and how many photons arrive using a digital oscilloscope. Then, as shown in FIG. 4B, the output value must be stored in the memory in 256 gradations (8 bits) every 1 ns in the time axis direction, whereas the light measurement according to the present embodiment is performed. If the device 10 is used, FIG.
As shown in (1), the number of photons of up to four gradations (2 bits) and the time information at that time need only be stored in the memory only when the photons are incident. That is, when the optical measurement device 10 according to the present embodiment is used, if a measurement time is 150 s and a time resolution is 5 ns, a memory of 64 Mbytes can be used to measure and record up to a maximum of 16 M events (photon incidence). it can. In addition, the use of the external memory 20 enables measurement and recording for a longer time.

The optical measuring device 10 according to the present embodiment
In, by outputting the number of incident photons as a digital value by the A / D converter 30, the signal output from the A / D converter 30 can be directly stored in the memory 38 and displayed. It can also be displayed directly on the unit 22.

The optical measuring device 10 according to the present embodiment
By using the HPD 24 having the photocathode 24a and the avalanche photodiode 24b, the number of photons incident simultaneously (or at a very close timing) can be efficiently detected.

In the optical measuring device 10 according to the present embodiment, the HPD 24 is used as the light detecting means. However, this is a VLPC (Visual Light Photon).
Counter). VLPC consists of an arsenic-doped silicon substrate and a thin non-doped layer epitaxially grown on the silicon substrate. VLPC
Is cooled to about 7K, and avalanche multiplication occurs by applying about 7V, and a gain of about 5 × 10 ⁴ is obtained. The reason why such a high gain is obtained in VLPC is that
This is because the band gap can be considered to be equal to the ionization energy from the impurity level. Since the VLPC has such a high gain, similarly to the HPD, it is possible to distinguish and output the number of incident photons.

The optical measuring device 10 according to the present embodiment
The following modifications can be considered. An optical measurement device 50 according to a first modification will be described with reference to FIG.
In the optical measurement device 50, the reset signal is not output from the counter 34 to the peak hold circuit 24, but is output from the newly provided delay circuit 29 to the peak hold circuit 24. The trigger signal output from the comparator 36 is input to the delay circuit 29.

In such a configuration, when a photon enters the HPD 24, the input voltage of the comparator 36 becomes higher than the reference voltage, so that the comparator 36 outputs a trigger signal. A / D conversion circuit 30 receiving such a trigger signal
A / D converts the output signal from the peak hold circuit 28 and outputs it to the memory 38. The memory 38, which has also received the trigger signal, outputs the output signal from the A / D conversion circuit 30 and the time signal from the counter 34. And are stored. On the other hand, the trigger signal is delayed by the delay circuit 29 and then output to the peak hold circuit 28 as a reset signal. Therefore, the peak hold circuit 28 is reset after a predetermined time has elapsed from the output of the trigger signal from the comparator 36.

FIG. 6 is a timing chart showing the operation of the optical measuring device 50. The operation of the optical measurement device 50 differs from the optical measurement device 10 according to the above-described embodiment in that
The point is that the peak hold circuit 28 is reset in response to the generation of a trigger signal from, that is, in response to the incidence of a photon. Here, the reset signal is output from the comparator 3
6 is delayed by a predetermined time by the delay circuit 29, the timing signal A /
After the A / D conversion is performed by the D conversion circuit 30, the peak hold circuit 28 is reset. With such a configuration, even if a plurality of photons are sequentially incident within the reset interval in the optical measurement device 10 according to the embodiment, it is possible to record the number of incident photons and the time of each photon.

FIG. 7 is a configuration diagram of an optical measurement device 60 according to the second modification. In the optical measurement device 10 according to the above-described embodiment, the current signal output from the HPD 24 is converted into a voltage by the TZ amplifier 26, and the peak hold circuit 28 outputs an output signal holding a peak value for a certain period. This is the optical measurement 6 according to this modification.
A charge amplifier 40 with a reset function such as 0 may be used. The charge amplifier 40 has one input terminal grounded, the other input terminal supplied with the output current of the HPD 24, and the output terminal connected to the input terminal of the A / D converter 30 and the comparator 3.
6, an operational amplifier 40a connected to the + input terminal, a capacitor 40b connecting the other input terminal and the output terminal of the operational amplifier 40a, and a reset switch 40c connected in parallel with the capacitor 40b. Be composed. Here, the charge amplifier 40 integrates and outputs the charge amount output from the HPD 24, and turns on the reset switch 40c by a reset signal from the counter 34.
Is reset. In the optical measuring device 60, the counter 34 of the time signal output unit 14 outputs a read signal immediately before outputting the reset signal.
On the other hand, an AND circuit 42 is provided downstream of the comparator 36 in the storage unit 16. The read signal output from the counter 34 and the trigger signal output from the comparator 36 are input to the AND circuit 42, and the output signal of the AND circuit is transmitted to the A / D converter 30 and the memory 38. Output. Therefore, in the optical measurement device 60,
After the output voltage from the charge amplifier 40 exceeds the reference voltage, when the read signal is output from the counter 34, the A / D conversion circuit 30 performs A / D conversion,
An output signal from the A / D conversion circuit 30 and a time signal from the counter 34 are stored in the memory 38. With this configuration, the peak hold circuit 28 becomes unnecessary. Further, even when a plurality of photons are continuously incident in a short time, errors can be minimized.

The optical measuring device 1 according to the above embodiment
In the case of 0, the counter 34 is reset by a reset signal from the CPU 18 at the start of measurement. However, the counter 34 may be reset by a trigger signal of the comparator 36. With this configuration, the counter 34 is reset with the incidence of photons, and the time signal output from the counter 34 is
This indicates the interval at which photons are incident on the HPD 24. Therefore, by adopting such a configuration, the memory 38 has the HP
The number of photons incident on D24 and the interval between incident photons are stored.

The optical measuring device 1 according to the above embodiment
At 0, the APD 24b is used as a semiconductor photodetector, but this may be a photodiode or the like.

[0050]

The optical measuring device and the optical measuring method according to the present invention are:
By storing a time signal when a photon is detected, it is possible to measure "when the photon has come". On the other hand, when no photons are detected, since no information is stored, the amount of data stored as a whole is extremely small. as a result,
It is possible to measure "when the photon came" over a long period of time.

In the optical measuring device and the optical measuring method of the present invention, when a photon is detected, the number and the time signal of the photon are stored, so that "when and how many photons came"
Can be measured. On the other hand, when no photons are detected, since no information is stored, the amount of data stored as a whole is extremely small. As a result, it is possible to measure "when and how many photons came" over a long period of time.

Further, in the optical measurement device of the present invention, by outputting the number of incident photons as a digital value, the signal output from the photon detection means can be stored directly by the storage means.

Further, in the optical measuring device of the present invention, a photocathode for emitting photoelectrons according to the number of incident photons, an accelerating means for accelerating photoelectrons, and an avalanche for outputting an output signal according to the number of photoelectrons. By using a photon detecting means including a semiconductor photodetector such as a photodiode, the number of photons incident simultaneously (or at a very close timing) can be efficiently detected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical measurement device.

FIG. 2 is an output wave height distribution diagram for a multiphoton.

FIG. 3 is a timing chart showing the operation of the optical measurement device.

FIG. 4 is a timing chart showing an effect of the optical measurement device.

FIG. 5 is a configuration diagram of an optical measurement device.

FIG. 6 is a timing chart showing the operation of the optical measurement device.

FIG. 7 is a configuration diagram of an optical measurement device.

[Explanation of symbols]

10, 50, 60: optical measurement device, 12: photon detector, 1
4 time signal output unit, 16 storage unit, 18 CPU, 2
0: external memory, 22: display unit, 24: HPD, 26 ...
TZ amplifier, 28: peak hold circuit, 30: A / D
Converter, 32 timer, 34 counter, 36 comparator, 38 memory, 40 charge amplifier

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Morita Tetsuya 1126 Nomachi, Ichinomachi, Hamamatsu City, Shizuoka Prefecture Inside Tonics Co., Ltd. F-term (reference) in Tonics Corporation 2G065 AA20 AB04 BA09 BA17 BC08 BC17 BC22 BC28 BC33 DA13 DA20

Claims (7)

[Claims] 1. A photon detection means for detecting an incident photon, a time signal output means for outputting a time signal, and a time signal output from the time signal output means when a photon is detected by the photon detection means. An optical measurement device, comprising: storage means for storing 2. The photon detection means detects the number of incident photons, and the storage means, when detecting photons by the photon detection means, detects the number of photons detected by the photon detection means; 2. The optical measurement device according to claim 1, wherein a time signal output from the time signal output means is stored. 3. The photodetector according to claim 2, wherein the photon detector has an A / D converter, and the A / D converter outputs the number of incident photons as a digital value. Optical measuring device. 4. A photocathode for emitting photoelectrons according to the number of incident photons, an accelerating means for accelerating the photoelectrons emitted from the photocathode, and an accelerating means for accelerating the photoelectrons. The optical measurement device according to claim 2, further comprising: a semiconductor photodetector that receives the photoelectrons and outputs an output signal corresponding to the number of the photoelectrons. 5. The optical measurement device according to claim 4, wherein the semiconductor photodetector is an avalanche photodiode. 6. A photon detecting step of detecting an incident photon, a time signal outputting step of outputting a time signal, and a time signal outputted by the time signal outputting step when a photon is detected by the photon detecting step. And a storing step of storing the light. 7. The photon detecting step, wherein a plurality of incident photons are separated and detected, and the storing step is the number of photons detected by the photon detecting step when the photons are detected by the photon detecting step. 7. The optical measurement method according to claim 6, wherein a time signal output in the time signal output step is stored.