Method and system for determining calibration parameters of PMT photon counting detector
Through the monochrome light source and orthogonal coordinate system fitting technology with gradient linear regulation, the nonlinear problem of PMT photon counting detector in the high response region is solved, and the accurate calibration of pulse resolution time and the count value compensation of the high response region is realized. , improves the effectiveness and accuracy of the system.
Patent Information
- Application Number
- CN202411037256.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-31
- Publication Date
- 2024-12-13
AI Technical Summary
The PMT photon count detector has nonlinear problems in the low response region and the high response region, which makes it a technical problem to accurately measure the resolution time of the pulse, especially due to the different response curves caused by the circuit differences within each PMT photon counter.
Using a monochromatic light source with linear regulation, the spectroscopic beam is used to perform linear change and attenuation processing in the reference detector and the PMT photon counting detector, the orthogonal coordinate system is established for fitting, and the theoretical number of pulses in the high response area is calculated and performed. Compensation, and then determine the pulse pair resolution time.
The accurate calibration of the PMT photon counting detector is realized, which improves the counting accuracy of the high response area and the certainty of the pulse resolution time, ensuring the effectiveness and high accuracy of the system.
Smart Images
Figure CN119124369A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of optoelectronic technology, and in particular to a method and system for determining calibration parameters of a PMT photon counting detector. Background Art
[0002] PMT (Photomultiplier Tube) photon counting detector is usually composed of PMT and supporting high-voltage circuits, amplifier circuits, pulse conversion circuits, pulse shaping drive circuits, etc. It can detect extremely weak light. The received light intensity is proportional to the output pulse, and the detection light intensity range is more than 6 orders of magnitude.
[0003] PMT photon counting detectors have certain nonlinearity in both low and high response areas, and there are differences between different PMTs. The output lower limit is generally determined by dark current and dark noise, and is generally within 100 to 10,000 pulses per second in the low response area; high response is generally more than several million pulses per second.
[0004] When calibrating a PMT photon counting detector, the low response area is generally below the dark count, and the dark count needs to be deducted when used to solve the calibration problem. The high response area generally requires the output value to be lower than the actual value, which requires calculation and compensation. The maximum count value in the high response area is determined by the maximum count rate, and the maximum count rate is determined by the minimum resolution time of two pulses (pulse pair resolution time). In addition, there are differences in the internal circuits of each PMT photon counter, resulting in different high-value response curves due to different times. Therefore, how to accurately measure the pulse pair resolution time has become a technical problem. Summary of the invention
[0005] The present invention aims to disclose a method and system for determining calibration parameters of a PMT photon counting detector, so as to accurately and effectively determine the pulse pair resolution time.
[0006] To achieve the above object, the method for determining the calibration parameters of a PMT photon counting detector disclosed in the present invention comprises:
[0007] Split the monochromatic light source whose light intensity can be linearly controlled according to the gradient into two;
[0008] Determine the light intensity distribution points and the unified gate time of the monochromatic light source sampling, and at each light intensity distribution point, use a reference detector to count the reference index of the linear change of the light intensity of the first split light beam within the gate time; at the same time, transmit the second split light beam to the PMT photon counting detector after attenuation processing according to a unified ratio, and then use a pulse counter to count the actual number of pulses of the PMT photon counting detector within the gate time;
[0009] An orthogonal coordinate system is established, wherein the reference index and the actual number of pulses are used as coordinate axes respectively, and sampling data of the coordinate system in the middle response area is selected for fitting to obtain a linear equation;
[0010] The theoretical pulse numbers corresponding to each reference index in the high response area are calculated according to the linear equation, and each of the theoretical pulse numbers is used as the compensated count value. Then, the pulse pair resolution time corresponding to each sampling point in the high response area is calculated according to the pulse pair compensation equation, and the final pulse pair resolution time of the PMT photon counting detector is obtained by averaging the pulse pair resolution times.
[0011] To achieve the above object, the present invention further discloses a system for determining calibration parameters of a PMT photon counting detector, comprising:
[0012] A device for dividing a monochromatic light source whose light intensity can be linearly regulated according to a gradient into two;
[0013] A controller for controlling the state of an optical path, the controller comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the following steps when executing the computer program:
[0014] Step S1, determining the light intensity distribution points and the unified gate time of the monochromatic light source sampling, and at each light intensity distribution point, using a reference detector to count the reference index of the first split light beam that changes linearly with the light intensity within the gate time; at the same time, the second split light beam is transmitted to the PMT photon counting detector after being attenuated at a uniform ratio, and then the actual number of pulses of the PMT photon counting detector within the gate time is counted by a pulse counter;
[0015] Step S2, establishing an orthogonal coordinate system, wherein the reference index and the actual number of pulses are used as coordinate axes respectively, and sampling data of the coordinate system in the middle response area are selected for fitting to obtain a linear equation;
[0016] Step S3, calculating the theoretical pulse numbers corresponding to each reference index in the high response area according to the linear equation, taking each theoretical pulse number as the compensated count value, and then calculating the pulse pair resolution time corresponding to each sampling point in the high response area according to the pulse pair compensation equation, and averaging the pulse pair resolution times to obtain the final pulse pair resolution time of the PMT photon counting detector.
[0017] Based on the above method and system, the pulse pair compensation equation is specifically:
[0018] Nout = Nin / (1-Nin*t);
[0019] Among them, Nout is the count value after compensation, Nin is the actual number of pulses, and t is the pulse pair resolution time.
[0020] Preferably, the monochromatic light source uses an adjustable constant current source as a driving power source; the reference detector can be a PD (Photo Diode) detector, a PIN (Positive Intrinsic-Negative) sensor, an APD (Avalanche Photo Diode) sensor, a phototube or a spectrometer. The processing of the reference index includes: amplifying the converted analog signal with a reference detector, then counting the amplified analog signal with an ADC, and using the obtained count value as the reference index.
[0021] Therefore, the method and system disclosed in the present invention are highly effective and accurate.
[0022] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:
[0024] Figure 1 It is a system block diagram for determining calibration parameters of a PMT photon counting detector disclosed in an embodiment of the present invention.
[0025] Figure 2 It is a schematic diagram of the distribution of sampling data disclosed in an embodiment of the present invention.
[0026] Figure 3 It is a schematic diagram of linear fitting of the intermediate response area according to an embodiment of the present invention.
[0027] Figure 4 It is a flow chart of a method for determining calibration parameters of a PMT photon counting detector disclosed in an embodiment of the present invention. DETAILED DESCRIPTION
[0028] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.
[0029] Example 1
[0030] This embodiment first discloses a system for calibrating parameters of a PMT photon counting detector, such as Figure 1As shown, the system includes a monochromatic light source and its matching adjustable constant current circuit, a reference PD detector and its matching amplification circuit, a PMT photon counting detector and its matching pulse counter, a main controller and other parts, which are responsible for calibrating the technical indicators of the detector such as sensitivity, gradient, linearity, stability, etc. The system consists of hardware circuit boards, optical components, mounting structures, control software, etc. The working process of the system is that the adjustable light source generates light with linear gradient changes, and the light is separated by the optical spectrometer system to generate two paths of light with different intensities, which are output to the reference PD detector and the PMT photon counting detector respectively. The PD detector, the PMT photon counting detector and its supporting circuits convert the light signal into numerical values respectively, and different light intensity levels obtain different numerical values. The linear response equation of the light signal of the PMT photon counting detector can be obtained by linearly fitting these two sets of numerical values. Different PMT photon counting detectors are calibrated using the same system, and different response equations can be obtained to calibrate the output data to a unified range to solve the consistency problem.
[0031] Furthermore, for Figure 1 The components are described as follows:
[0032] Monochromatic light source: provides the system with a light source with adjustable light intensity, generally using monochromatic LED or LD. The greater the working current of LED and LD, the stronger the output light intensity; if the light source transmits a spectrum range, the single wavelength capability can be further improved by adding filters; and when the light power is large, a heat dissipation device needs to be configured to prevent the light source from overheating and damage.
[0033] Adjustable constant current source: Provides constant current driving power for monochromatic light sources, adjusts output current through digital interface, generally uses linear constant current circuit for adjustment, adapts different working current ranges according to different light sources, and ensures that the light source works under the best conditions.
[0034] PD detector: It can be a conventional semiconductor photodiode. The received light intensity is proportional to the reverse current. It has a fast response speed, a wide range, strong anti-interference, a simple circuit, and a weaker response sensitivity than the electron tube PMT. It can be used in conjunction with a dedicated transimpedance amplifier circuit.
[0035] Multi-speed amplifier: A supporting circuit for the PD detector, responsible for converting the PD signal current into an amplifier circuit suitable for the ADC voltage. It generally uses 3 to 5 amplification gears to meet the needs of different usage ranges and expand the response dynamic range of the PD signal. A logarithmic amplifier circuit can also be used to expand the dynamic range to match the response range of the PMT.
[0036] Optical attenuator: It is a physical structure optical attenuation device. Since the PMT response sensitivity is high and the light source signal is too strong to be detected directly, a physical attenuator is used to attenuate the optical power at a fixed ratio to meet the detection sensitivity requirements of the PMT.
[0037] PMT photon counting detector: the target device for calibration.
[0038] Pulse counter: responsible for receiving and processing the digital pulse signal of the PMT photon counter. It is responsible for adjusting the signal level and impedance matching and recording the number of pulses within the gate time and transmitting it to the controller.
[0039] Controller: Responsible for the overall logic control and calibration process scheduling of the device. The general workflow is to receive the operating instructions of the host computer, control the brightness of the light source, receive the calculated value of the detector, upload it to the host computer, perform scheduling and communication interface conversion, etc.
[0040] Host computer software: generally refers to software running on the computer, responsible for human-computer interaction, data algorithms, etc. It calculates fitting parameters according to a fixed algorithm. After calibration, the calibrated data results can also be calculated according to the calculation formula.
[0041] In this embodiment, Figure 1 The principle of the system shown is to use the good response linearity and stability of the PD to calibrate the linearity and stability of the PMT. Linear calibration requires the use of a monochromatic light source with adjustable brightness and the optical power variation level needs to reach more than 40dB.
[0042] based on Figure 1The calibration process of the system is as follows: the monochromatic light source provides the optical signal for the calibration system, and the adjustable constant current source drives the monochromatic light source in a constant current mode. The current and the light intensity are in a positive linear relationship. The larger the current, the stronger the light emitted by the light source. The controller adjusts the light intensity between 0-40dB. Due to the high detection sensitivity of the PMT, an optical attenuation plate is used for attenuation and detection, and the PD directly detects the light of the light source. The PMT photon counting detector uses a pulse counter to digitize the signal. The linear amplification circuit of the PD detector cannot cover the 0-40dB range and requires a multi-speed switching amplification factor to digitize the signal. Under the control of the upper computer software, each time the light intensity is adjusted, the two detectors record data respectively. Since the PMT photon counting detector has a better response result with the PD in the middle response range, Linear response correlation. Based on these data, a first-order linear equation can be fitted, and the linear correlation is above 99.99%. Based on this first-order linear equation, the PMT theoretical output value of the high response area can be calculated according to the PD value of the high response area. This theoretical calculated value is the output Nout value in the pulse pair resolution time calculation formula, which is the count value after compensation. At the same time, the actual measurement of the PMT photon counting detector corresponding to the PD value of the high response area is the input Nin value, which is the count value before compensation. The pulse pair resolution time t can be calculated according to the compensation calculation formula. This pulse pair resolution time t is the high-value calibration parameter of the optical signal of this PMT photon counting detector. Multiple PMT photon counting detectors developed can be calibrated based on this system and method, and better high-value linearity can be achieved after calibration.
[0043] The specific fitting and pulse pair compensation equation calculation formulas are detailed as follows:
[0044] If the light source current is adjusted proportionally, in the test data, as shown in Table 1 and Figure 2 As shown, the PD signal increases linearly and proportionally, and the PMT detector value shows nonlinearity in the high response area.
[0045] Table 1: Test data
[0046]
[0047] exist Figure 2 In the orthogonal coordinate system established in , the actual number of pulses obtained by the pulse counter and the reference index and obtained by the PD detector are each a coordinate axis, and the linearity of the middle section is better. Therefore, the sampling data of the coordinate system in the middle response area are selected for fitting to obtain the linear equation as follows: Figure 3 shown.
[0048] In this embodiment, the pulse pair compensation equation is: Nout=Nin / (1-Nin*t); wherein Nout is the count value after compensation, Nin is the actual number of pulses, and t is the pulse pair resolution time.
[0049] The system of this embodiment includes a device for dividing a monochromatic light source whose light intensity can be linearly controlled according to a gradient into two. In conjunction with the device, the controller of this embodiment includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor implements the following steps when executing the computer program:
[0050] Step S1, determine the light intensity distribution points and the unified gating time of the monochromatic light source sampling, and at each light intensity distribution point, use a reference detector to count the reference index of the first split light beam that changes linearly with the light intensity within the gating time; at the same time, the second split light beam is transmitted to the PMT photon counting detector after attenuation processing at a uniform ratio, and then a pulse counter is used to count the actual number of pulses of the PMT photon counting detector within the gating time.
[0051] In this step, optionally, the reference detector can be a PD detector, a PIN sensor, an APD sensor, a photoelectric tube or a spectrometer. Preferably, the processing of the reference index includes: amplifying the converted analog signal with a reference detector, and then counting the amplified analog signal with an ADC, and using the obtained count value as a reference index. Among them, the ADC acquisition accuracy is higher, so that the subsequent linear fitting equation can be more accurate. As an implementation with deterioration in accuracy, the reference index can also be directly replaced by the analog voltage before and after amplification.
[0052] Step S2, establishing an orthogonal coordinate system, wherein the reference index and the actual number of pulses are respectively used as coordinate axes, and sampling data of the coordinate system in the middle response area are selected for fitting to obtain a linear equation.
[0053] In this step, the specific range of the intermediate response area can be flexibly selected by the user based on experience to better satisfy the linear relationship.
[0054] Step S3, calculating the theoretical pulse numbers corresponding to each reference index in the high response area according to the linear equation, taking each theoretical pulse number as the compensated count value, and then calculating the pulse pair resolution time corresponding to each sampling point in the high response area according to the pulse pair compensation equation, and averaging the pulse pair resolution times to obtain the final pulse pair resolution time of the PMT photon counting detector.
[0055] Example 2
[0056] Corresponding to the above embodiment, this embodiment discloses a method for determining the calibration parameters of a PMT photon counting detector, such as Figure 4 As shown, the following steps are included:
[0057] Step S21, dividing the monochromatic light source whose light intensity can be linearly controlled according to the gradient into two.
[0058] Step S22, determine the light intensity distribution points and the unified gating time for sampling the monochromatic light source, and at each light intensity distribution point, use a reference detector to count the reference index of the first split light beam that changes linearly with the light intensity within the gating time; at the same time, the second split light beam is attenuated at a uniform ratio and then transmitted to the PMT photon counting detector, and then a pulse counter is used to count the actual number of pulses of the PMT photon counting detector within the gating time.
[0059] Step S23, establishing an orthogonal coordinate system, wherein the reference index and the actual number of pulses are respectively a coordinate axis, and selecting sampling data of the coordinate system in the middle response area for fitting to obtain a linear equation.
[0060] Step S24, calculating the theoretical number of pulses corresponding to each reference index in the high response area according to the linear equation, taking each of the theoretical number of pulses as the compensated count value, and then calculating the pulse pair resolution time corresponding to each sampling point in the high response area according to the pulse pair compensation equation, and averaging the pulse pair resolution times to obtain the final pulse pair resolution time of the PMT photon counting detector.
[0061] The specific implementation of each step can refer to Example 1 and will not be described in detail.
[0062] In summary, the method and system disclosed in the embodiments of the present invention are highly effective and accurate, and are easy to promote and implement.
[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.
Claims
1. A method for determining calibration parameters of a PMT photon counting detector, It is characterized in that include: Split the monochromatic light source whose light intensity can be linearly controlled according to the gradient into two; Determine the light intensity distribution points and the unified gate time of the monochromatic light source sampling, and at each light intensity distribution point, use a reference detector to count the reference index of the linear change of the light intensity of the first split light beam within the gate time; at the same time, transmit the second split light beam to the PMT photon counting detector after attenuation processing according to a unified ratio, and then use a pulse counter to count the actual number of pulses of the PMT photon counting detector within the gate time; An orthogonal coordinate system is established, wherein the reference index and the actual number of pulses are used as coordinate axes respectively, and sampling data of the coordinate system in the middle response area is selected for fitting to obtain a linear equation; The theoretical pulse numbers corresponding to each reference index in the high response area are calculated according to the linear equation, and each of the theoretical pulse numbers is used as the compensated count value. Then, the pulse pair resolution time corresponding to each sampling point in the high response area is calculated according to the pulse pair compensation equation, and the final pulse pair resolution time of the PMT photon counting detector is obtained by averaging the pulse pair resolution times.
2. The method according to claim 1, It is characterized in that The reference detector is a PD detector, a PIN sensor, an APD sensor, a photoelectric tube or a spectrometer.
3. The method according to claim 1, It is characterized in that The pulse pair compensation equation is: Nout = Nin / (1-Nin*t); Among them, Nout is the count value after compensation, Nin is the actual number of pulses, and t is the pulse pair resolution time.
4. The method according to claim 1, 2 or 3, It is characterized in that The processing process of the reference indicator includes: amplifying the converted analog signal with a reference detector; The amplified analog signal is counted by ADC, and the obtained count value is used as the reference index.
5. The method according to claim 1, 2 or 3, It is characterized in that The monochromatic light source uses an adjustable constant current source as a driving power source.
6. A system for determining calibration parameters of a PMT photon counting detector, It is characterized in that include: A device for dividing a monochromatic light source whose light intensity can be linearly regulated according to a gradient into two; A controller for controlling the state of an optical path, the controller comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the following steps when executing the computer program: Step S1, determining the light intensity distribution points and the unified gate time of the monochromatic light source sampling, and at each light intensity distribution point, using a reference detector to count the reference index of the first split light beam that changes linearly with the light intensity within the gate time; at the same time, the second split light beam is transmitted to the PMT photon counting detector after being attenuated at a uniform ratio, and then the actual number of pulses of the PMT photon counting detector within the gate time is counted by a pulse counter; Step S2, establishing an orthogonal coordinate system, wherein the reference index and the actual number of pulses are used as coordinate axes respectively, and sampling data of the coordinate system in the middle response area are selected for fitting to obtain a linear equation; Step S3, calculating the theoretical pulse numbers corresponding to each reference index in the high response area according to the linear equation, taking each theoretical pulse number as the compensated count value, and then calculating the pulse pair resolution time corresponding to each sampling point in the high response area according to the pulse pair compensation equation, and averaging the pulse pair resolution times to obtain the final pulse pair resolution time of the PMT photon counting detector.
7. The system according to claim 6, It is characterized in that The reference detector is a PD detector, a PIN sensor, an APD sensor, a photoelectric tube or a spectrometer.
8. The system according to claim 6, It is characterized in that The pulse pair compensation equation is: Nout = Nin / (1-Nin*t); Among them, Nout is the count value after compensation, Nin is the actual number of pulses, and t is the pulse pair resolution time.
9. A system according to claim 6, 7 or 8, It is characterized in that The processing process of the reference indicator includes: amplifying the converted analog signal with a reference detector; The amplified analog signal is counted by ADC, and the obtained count value is used as the reference index.
10. The system according to claim 6, 7 or 8, It is characterized in that The monochromatic light source uses an adjustable constant current source as a driving power source.