Noise evaluation method for photoelectric detector

Abstract

The invention discloses a photoelectric detector noise evaluation method. The method comprises the following steps: 1) selecting a large-size photoelectric detector to be evaluated, wherein the large-size photoelectric detector comprises a large-size photoelectric device, a readout electronics circuit, a photoelectric device power supply device and a readout electronics circuit power supply device; the large-size photoelectric device comprises a plurality of small-size photoelectric devices; each large-size photoelectric device or a certain small-size photoelectric device of the large-size photoelectric devices is independent by the single-path readout electronics circuit for independent power supply and signal readout, and the signals are transmitted to the signal acquisition device; 2) the signal acquisition device unifies or normalizes noise discrete evaluation standards of the detector and each part to evaluation standards with physical significance; and 3) performing decomposition evaluation on each selected part of the large-size photoelectric detector by adopting a trigger rate scanning method. The method has high universality and compatibility for photoelectric devices of different models, light sources of different wavelengths and signal acquisition devices of different types.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of particle detection, and relates to a photoelectric detector noise evaluation method for noise evaluation of photoelectric devices and readout electronic circuits thereof. BACKGROUND

[0002] As a new type of semiconductor photon detector, the silicon photomultiplier (SiPM) has been widely used in high-energy physics experiments, medical imaging (such as PET / MRI), laser radar (LiDAR), quantum communication and dark matter detection in recent years, and its core advantages are high gain, low operating voltage, compact size and excellent single photon sensitivity.

[0003] The performance evaluation of the SiPM detector mainly focuses on the dark count rate, dynamic range, charge resolution, linearity and signal-to-noise ratio. In actual operation, how many threshold values will reach what level of trigger rate? In physical analysis, what is the physical level of the detection lower limit of the detector? These problems are new requirements derived from the practical application of the SiPM detector. SUMMARY

[0004] In view of the problems in the prior art, the purpose of the present application is to provide a photoelectric detector noise evaluation method. The large-size photoelectric detector to be evaluated includes a large-size photoelectric device, a readout electronic circuit, a photoelectric device power supply and a readout electronic power supply. The photoelectric device converts the optical signal into an electrical signal through ionization collision. The large-size photoelectric device can improve the light receiving area and dynamic range of the photoelectric detector. The large-size photoelectric device is spliced by N (N≥1) small-size photoelectric devices, wherein the cathodes of the small-size photoelectric devices are connected to the same power supply device (i.e. the photoelectric device power supply) for power supply through an isolation filtering mode, and the avalanche signals of the small-size photoelectric devices are combined and read out to the readout electronic circuit through the anodes of the small-size photoelectric devices. The method can quantitatively evaluate the noise contribution of each part of the photoelectric detector from the perspective of the number of photoelectrons at the physical level, and can evaluate the noise levels of different photoelectric devices, different readout electronic schemes and different power supply schemes.

[0005] The technical scheme of the present application is as follows:

[0006] A photoelectric detector noise evaluation method, the steps of which include:

[0007] 1) selecting a large-size photoelectric detector to be evaluated, which includes a large-size photoelectric device, a readout electronic circuit, a photoelectric device power supply and a readout electronic power supply; the large-size photoelectric device includes a plurality of small-size photoelectric devices;

[0008] A light shielding cover is arranged at the front end of the large-size photodetector, for adjusting the incident light signal;

[0009] 2) Adjust the number of photons received by the small-size photodetector to be measured by adjusting the light source brightness and the size of the light shielding cover, until the number of photoelectrons reaches the single photoelectron level; use single-channel readout electronics to independently power and signal readout of the small-size photodetector to be measured, and amplify and shape the readout analog pulse signal to transmit to the signal acquisition device;

[0010] 3) The signal acquisition device calculates the absolute gain G1 of the small-size photodetector to be measured and the single-channel readout electronics connected thereto according to the received signal;

[0011] 4) Keep the state of the small-size photodetector to be measured unchanged, adjust the light intensity reaching the small-size photodetector to be measured by adjusting the light source brightness; then use the single-channel readout electronics to read out the signal generated by the small-size photodetector to be measured and amplify and shape it to transmit to the signal acquisition device for processing, to obtain the pulse amplitude mean value S ph of the small-size photodetector to be measured; and then use the absolute gain G1, the pulse amplitude mean value S ph , and the light transmission area A mask of the light shielding cover to calculate the photoelectron density ρ pe on the plane where the small-size photodetector to be measured is located;

[0012] 5) Insert the large-size photodetector into the merging readout electronics of the large-size photodetector to be evaluated for merging readout, and set the power supply voltage of the large-size photodetector to be the same as that of the small-size photodetector to be measured;

[0013] 6) Keep the light source emission parameters consistent with step 4), and place the large-size photodetector at the plane and position where the small-size photodetector to be measured is located when calibrating the photoelectron density of the small-size photodetector to be measured; the merging readout electronics reads out the signal generated by the large-size photodetector and amplifies and shapes it to transmit to the signal acquisition device for processing, to obtain the response pulse amplitude S ph-large of the large-size photodetector; and then use the photoelectron density ρ pe to calibrate the amplitude gain G2 of the large-size photodetector;

[0014] 7) Change the light source emission intensity multiple times, repeat steps 4) to 6), and verify the accuracy and repeatability of the amplitude gain of the large-size photodetector; when the accuracy and repeatability meet the set conditions, use the median value of the amplitude gain G2 obtained multiple times as the final amplitude gain G2 of the large-size photodetector;

[0015] 8) Decompose and evaluate each selected component of the large-size photodetector by trigger rate scanning method; the trigger rate scanning method is:

[0016] 81) Set the amplitude trigger threshold Th mV Unify the final amplitude gain G2 of the large-size photodetector to the evaluation standard of the number of photoelectrons, and obtain the trigger threshold Th pe ;

[0017] 82) Irradiate the large-size photodetector with a light source with a known emission frequency, change the trigger threshold Th pe multiple times, count the number of rising edges or falling edges of the pulse signal in the sampling time window of the signal acquisition device that pass through the trigger threshold Th pe , divide the count by the length of the sampling time window to obtain the trigger rate, and plot the trigger rate scanning results of the large-size photodetector using the trigger rates obtained multiple times;

[0018] 83) Isolate each selected component of the large-size photodetector step by step, and repeat step 82);

[0019] 84) Obtain the overall noise evaluation of the large-size photodetector according to the trigger rate scanning results of step 82), and obtain the noise evaluation of each selected component according to the trigger rate scanning results of step 83).

[0020] Further, by adjusting the brightness of the light source and the size of the light shield, the number of photons received by the small-size photodetector under test is adjusted until the number of photoelectrons responded by the small-size photodetector under test reaches the single photoelectron level.

[0021] Further, the light source control device is used to control the light source to emit light and trigger the acquisition device to sample the received signal.

[0022] Further, the single-channel readout electronics circuit is connected to the large-size photodetector through a connector for independent power supply and signal readout of each small-size photodetector under test.

[0023] Further, the photoelectron number density The amplitude gain Where A large is the effective light receiving area of the large-size photodetector during testing.

[0024] Further, the trigger threshold

[0025] Further, each small-size photovoltaic device cathode is powered by an isolated filter mode to access the power supply of the photovoltaic device; and the avalanche signals of each small-size photovoltaic device are read out to the readout electronics circuit through the anode.

[0026] Further, when the accuracy and repeatability of the amplitude gain of the large-size photodetector meet the set conditions, the median value of the amplitude gain G2 obtained by multiple times is used as the pulse amplitude gain of the large-size photodetector.

[0027] Further, the amplified and shaped analog pulse signals are transmitted to the signal acquisition device through a coaxial line.

[0028] The advantages of the present application are as follows:

[0029] The present application realizes the quantification from the physical layer and the perspective of the number of optoelectronic devices, and decomposes the noise contribution of each part of the photodetector, and can evaluate the noise level of different photovoltaic devices, different readout electronics schemes, and different power supply schemes. The noise evaluation method has high universality and compatibility for different models of photovoltaic devices, different wavelengths of light sources, and different types of signal acquisition devices. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The working principle diagram of the trigger rate test.

[0031] The figure shows: 1-light source; 2-light source power supply device; 3-light source control device; 4-light shielding cover; 5-SiPM detector; 6-SiPM power supply; 7-readout electronics power supply; 8-signal acquisition device; 9-darkroom. DETAILED DESCRIPTION

[0032] The present application will be further described in detail below with reference to the accompanying drawings, and the examples are only used to explain the present application, and not to limit the scope of the present application.

[0033] The device involved in the method of the present application includes a single-channel readout electronics circuit, a signal acquisition device, a light source, a power supply, and a light shielding cover (Mask). Among them:

[0034] The single-channel readout electronics circuit separates each or a certain small-size photovoltaic device from the large-size photovoltaic device, that is, independently powers and reads out the signals of the separated small-size photovoltaic device. The single-channel readout electronics circuit also amplifies and shapes the analog pulse signals output by the small-size photovoltaic device working independently, and then transmits them to the signal acquisition device through a coaxial line.

[0035] The signal acquisition device often outputs data in its own measurement standard (such as channel, ADC Count, volt, etc.), and does not have a unified evaluation standard in the process of evaluating the noise of the detector and each part, and does not have a physical evaluation standard.

[0036] A) By using the intrinsic characteristics that the noise of the semiconductor photoelectric device decreases with the decrease of the size area, the large-size photoelectric device in the large-size photoelectric detector is inserted into the single-channel readout electronics circuit through the connector, so that the small-size photoelectric device in the large-size photoelectric detector is separated from the working circuit, that is, the small-size photoelectric device is independently powered and signal readout.

[0037] B) By adjusting the brightness of the light source and the size of the light shield mask, the number of photons received by the small-size photoelectric device is adjusted, and the number of photoelectrons responding to the small-size photoelectric device after photoelectric conversion reaches several photoelectron levels. The light shield mask is arranged in front of the to-be-measured photoelectric detector, and is used for adjusting the incident light signal (i.e. the number of received photons).

[0038] C) The light source control device triggers the signal acquisition device to perform signal waveform triggering sampling in a delay triggering or synchronous triggering mode while controlling the light source to emit light. The light source control device is connected with the light source and the signal acquisition device respectively, and the light source is connected with the light source power supply device.

[0039] D) Finally, the pulse amplitude spectrum of each or some or a small-size photoelectric device under weak light irradiation is calculated, the discrete photoelectron spectrum of the small-size photoelectric device is obtained, the discrete photoelectron spectrum is fitted by using the "Poisson convolution Gaussian", or the distance between peaks of the discrete photoelectron spectrum is calculated, so that the absolute gain G1 of the small-size photoelectric device and the single-channel readout electronics circuit is calculated.

[0040] E) The working state (photoelectric device power supply voltage, environmental temperature) of the small-size photoelectric device and the single-channel readout electronics circuit is kept unchanged, the light source power supply device is adjusted to increase the light emitting brightness of the light source, and the light intensity reaching the surface of the small-size photoelectric device is further adjusted.

[0041] F) The light source control device triggers the signal acquisition device to perform signal waveform triggering sampling in a delay triggering or synchronous triggering mode while controlling the light source to emit light, and calculates the mean value S of the pulse amplitude of the small-size SiPM under the light irradiation condition. ph , the absolute gain G1 obtained in the step D), the light transmission area A of the mask mask , and the number density p of photoelectrons reaching the plane where the small-size SiPM is located and being sensed by the SiPM are calculated. pe(Formula F.1). The photon density reaching the SiPM surface is characterized in terms of photoelectron density, which also eliminates the differences in detection efficiency for different wavelengths in the same type of photoelectric device and for the same wavelength in different types of photoelectric devices.

[0042]

[0043] G) The large-size photoelectric device is inserted into the combined readout electronics circuit of the large-size photoelectric detector, and the large-size photoelectric device has the same power supply voltage as the small-size photoelectric device, so as to eliminate the differences in detection efficiency for the same wavelength in the same photoelectric device under different operating voltages.

[0044] H) The light source is kept in the same light emission parameters as in steps E) and F), and the large-size photoelectric detector is placed in the same plane and the same position as the small-size photoelectric device for measuring the photoelectron density, and the light source control device triggers the signal acquisition device to perform signal waveform triggering sampling by means of delayed triggering or synchronous triggering while controlling the light source to emit light, so as to calculate the response pulse amplitude S ph-large of the large-size photoelectric detector to the light source under the light emission conditions in steps E) and F). pe , and the amplitude gain G2 of the large-size photoelectric detector is calibrated.

[0045]

[0046] , where A large is the effective light receiving area of the large-size photoelectric detector during the test.

[0047] I) The light source emission intensity is changed multiple times, and steps E) to H) are repeated. The light source emission brightness is changed, and multiple light source intensity tests are performed to verify the accuracy and repeatability of the amplitude gain calibration of the large-size photoelectric detector. When the accuracy and repeatability meet the set conditions, the median value of the amplitude gain G2 obtained multiple times is used as the amplitude gain of the large-size photoelectric detector.

[0048] J) During the trigger rate scanning process, the amplitude trigger threshold Th mV of the signal acquisition device is unified to the evaluation standard of photoelectrons by the amplitude gain G2 of the large-size photoelectric detector.

[0049] K) Different types of photoelectric detectors need to be recalibrated through steps A) to J) to eliminate the differences in detection efficiency for the same wavelength in different photoelectric devices.

[0050] In the noise evaluation process, the trigger rate scanning method is used to decompose and evaluate each component of the detector. That is, by constantly changing the trigger threshold Th mVWhen the rising or falling edge of the pulse signal exceeds the threshold Th within the statistical sampling time window... pe The count is then divided by the sampling time window length to calculate the trigger rate (in Hertz (Hz)). The sampling time window length needs to increase as the trigger threshold increases to ensure that ≥M over-threshold events are recorded within a single sampling time window. The trigger threshold Th is expressed in units of amplitude from the signal acquisition device (assuming signal amplitude is expressed in volts V). mV The amplitude gain G2 of a large-size photodetector can be converted into a trigger threshold Th, measured in units of the number of photoelectrons pe. pe

[0051]

[0052] During the trigger rate scanning process, the photodetector is first illuminated with a light source of known emission frequency, and the trigger rate scanning results are plotted to verify the correctness of the trigger rate scanning results. Then, the individual components of the detector are gradually separated or replaced to perform trigger rate scanning under different detector states. Finally, the noise evaluation and contribution decomposition of the detector as a whole and its individual components are realized, and the noise levels of different accessories are further compared.

[0053] Assuming M=2, the photoelectric device is a silicon photomultiplier tube (SiPM), the test light source is an LED, the LED's emission frequency is 1000Hz, and the signal acquisition device is an oscilloscope. The noise level of the large-size SiPM detector will be tested through the following steps:

[0054] 1) Turn on the SiPM power supply to enable SiPM to work, turn on the LED light source and set the light emission frequency to 1000Hz;

[0055] 2) Turn on the SiPM power supply to enable SiPM operation; the LED light source will be off and not working.

[0056] 3) Turn off the SiPM power supply so that the SiPM does not work and the LED light source is turned off and does not work.

[0057] By continuously changing the trigger threshold, the number of rising or falling edges of the pulse signal exceeding the threshold within the oscilloscope's sampling time window is counted, and then divided by the sampling time window length to calculate the trigger rate (in Hertz (Hz)). The sampling time window length needs to be increased according to the increase of the trigger threshold to ensure that ≥2 over-threshold events are recorded within a single sampling time window. When the SiPM is working and the LED is on, the trigger rate plateau represents the frequency of the matched signal; when the SiPM is not working, it represents the electronic noise of the matched readout circuit; when the SiPM is working and the LED is off, it represents the dark noise level of the SiPM itself.

[0058] While specific embodiments of the application have been disclosed in order to illustrate the application and to assist those skilled in the art in practicing the application, it is to be understood that various substitutions, modifications and changes can be made by those skilled in the art without departing from the spirit of the application and the scope of the appended claims. Accordingly, it is intended that the application not be limited, except by the scope of the claims.

Claims

1. A method for evaluating the noise of a photodetector, comprising the following steps: 1) Select a large-size photodetector to be evaluated, which includes a large-size photoelectric device, a readout electronics circuit, a power supply for the photoelectric device, and a power supply for the readout electronics; the large-size photoelectric device includes multiple small-size photoelectric devices; A light shield is provided at the front end of the large-size photodetector to adjust the incident light signal; 2) By adjusting the brightness of the light source and the size of the light shield, the number of photons received by the small-sized optoelectronic device under test is adjusted until the number of photoelectrons in response reaches the level of a single photoelectron; the small-sized optoelectronic device under test is independently powered and the signal is read out using a single-channel readout electronics circuit, and the readout analog pulse signal is amplified and shaped before being transmitted to the signal acquisition device. 3) The signal acquisition device calculates the absolute gain G1 of the small-sized optoelectronic device under test and its connected single-channel readout electronics circuit based on the received signal; 4) Keeping the state of the small-sized optoelectronic device under test unchanged, the light intensity is adjusted to reach the small-sized optoelectronic device by adjusting the brightness of the light source; then, the signal generated by the small-sized optoelectronic device under test is read out using a single-channel readout electronic circuit, amplified and shaped, and then transmitted to the signal acquisition device for processing to obtain the average pulse amplitude S of the small-sized optoelectronic device under test. ph Then, using the absolute gain G1 and the average pulse amplitude S... ph and the light-transmitting area A of the light shield. mask Calculate the photoelectron number density ρ reaching the plane of the small-sized optoelectronic device under test. pe ; 5) Insert the large-size optoelectronic device back into the merging readout electronics circuit of the large-size photodetector to be evaluated, and set the power supply voltage of the large-size optoelectronic device to be the same as that of the small-size optoelectronic device to be tested; 6) Maintaining the light source emission parameters consistent with step 4), place the large-size photodetector at the plane and position where the small-size photodetector is located when calibrating the photoelectron number density of the small-size photodetector. The combined readout electronics circuit reads the signal generated by the large-size photodetector, amplifies and shapes it, and transmits it to the signal acquisition device for processing to obtain the response pulse amplitude S of the large-size photodetector. ph-large Then, using the photoelectron number density ρ pe The amplitude gain G2 of the large-size photodetector is calibrated. 7) Repeat steps 4) to 6) by changing the light intensity of the light source multiple times to check the accuracy and repeatability of the amplitude gain of the large-size photodetector; when the accuracy and repeatability meet the set conditions, use the median value of the amplitude gain G2 obtained multiple times as the final amplitude gain G2 of the large-size photodetector. 8) The selected components of the large-size photodetector are disassembled and evaluated using a trigger rate scanning method; the trigger rate scanning method is as follows: 81) Set the amplitude trigger threshold Th in the signal acquisition device. mV By unifying the final amplitude gain G2 of the large-size photodetector to the evaluation criterion of photoelectron count, the trigger threshold Th is obtained. pe ; 82) Illuminate the large-size photodetector with a light source of known emission frequency, and change the trigger threshold Th multiple times. pe The rising or falling edge of the pulse signal within the sampling time window of the signal acquisition device exceeds the trigger threshold Th. pe The trigger rate is obtained by dividing the count by the sampling time window length; the trigger rate scan results of the large-size photodetector are plotted using the trigger rates obtained multiple times. 83) Stepwise separate each selected component from the large-size photodetector, and repeat step 82); 84) Obtain the overall noise evaluation of the large-size photodetector based on the trigger rate scan results of step 82); obtain the noise evaluation of each selected component based on the trigger rate scan results of step 83).

2. The method according to claim 1, characterized in that, By adjusting the brightness of the light source and the size of the light shield, the number of photons received by the small-sized optoelectronic device under test is adjusted until the number of photoelectrons responded by the small-sized optoelectronic device under test reaches the level of a single photoelectron.

3. The method according to claim 2, characterized in that, The light source is controlled to emit light by the light source control device and the acquisition device is triggered to sample the received signal.

4. The method according to claim 1, 2, or 3, characterized in that, The single-channel readout electronics circuit is connected to the large-size optoelectronic device via a connector, and is used to independently power and read out signals from each small-size optoelectronic device under test.

5. The method according to claim 1, 2, or 3, characterized in that, The photoelectron number density The amplitude gain Among them, A large This refers to the effective light-receiving area of ​​the large-size photodetector during the testing process.

6. The method according to claim 1, 2, or 3, characterized in that, The trigger threshold 7. The method according to claim 1, 2, or 3, characterized in that, Each small-sized optoelectronic device's cathode is connected to the optoelectronic device's power supply via an isolation filter; the avalanche signals of each small-sized optoelectronic device are combined through their anodes and read out to the readout electronics circuit.

8. The method according to claim 1, characterized in that, When the accuracy and repeatability of the amplitude gain of the large-size photodetector meet the set conditions, the median value of the amplitude gain G2 obtained multiple times is used as the pulse amplitude gain of the large-size photodetector.

9. The method according to claim 1, characterized in that, The read analog pulse signal is amplified and shaped before being transmitted to the signal acquisition device via a coaxial cable.

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