Computing device, light detection device, and gain calculation method

Abstract

The operation device is a device that calculates a gain of a photomultiplier tube, and includes an acquisition unit that acquires a digital signal based on a dark pulse output from the photomultiplier tube in a state of being in darkness, and a calculation unit that calculates a total number of electrons of the dark pulse based on the digital signal, and calculates the gain of the photomultiplier tube based on the total number of electrons.

Description

Technical Field

[0001] This invention relates to a computing device, an optical detection device, and a gain calculation method. Background Technology

[0002] Light detection devices including photomultiplier tubes are known (e.g., Patent Document 1). In such light detection devices, the amount of light incident on the photomultiplier tube (incident light amount) is calculated based on the output signal from the photomultiplier tube.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-92774 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] To determine the incident light quantity from the output signal of the photomultiplier tube (PMT), the PMT's gain is used. This gain can vary depending on the environment and operating conditions around the PMT, therefore, gain measurement is required. A dedicated circuit for gain measurement has also been considered, but this increases circuit complexity.

[0008] This invention describes a computational device, a photodetector, and a gain calculation method that can suppress the complexity of circuit structure and calculate the gain of a photomultiplier tube.

[0009] Technical means to solve the problem

[0010] One aspect of the present invention is a computational device for calculating the gain of a photomultiplier tube. The computational device includes: an acquisition unit that acquires a digital signal based on a dark pulse output from the photomultiplier tube in a dark state; and a calculation unit that calculates the total number of electrons in the dark pulse based on the digital signal and calculates the gain based on the total number of electrons.

[0011] In this processing device, a digital signal based on a dark pulse output from a photomultiplier tube in darkness is acquired, and the total number of electrons in the dark pulse is calculated based on this digital signal. When the photomultiplier tube is in darkness, one hot electron is generated, and a dark pulse is generated by multiplying this one hot electron. Therefore, since the total number of electrons in the dark pulse is equivalent to the gain of the photomultiplier tube, the gain can be calculated based on the total number of electrons. In this way, since a dedicated circuit for measuring the gain is not required, the complexity of the circuit structure can be suppressed, and the gain of the photomultiplier tube can be calculated.

[0012] The digital signal can also be generated by quantizing the voltage signal obtained by converting the current to voltage of a dark pulse using a conversion factor through an amplifier at a sampling frequency via an AD converter. The computing unit can also calculate the total number of electrons based on the digital signal, the conversion factor, and the sampling frequency. In this case, since the conversion factor and sampling frequency used to generate the digital signal are taken into account, the accuracy of the total number of electrons calculation can be improved. As a result, the accuracy of the gain calculation can be improved.

[0013] The computing unit can also calculate the area of ​​the digital signal waveform. It multiplies the physical quantity per unit area (obtained by dividing the quantized amplitude of the A / D converter by the sampling frequency) and the reciprocal of the conversion coefficient by the area, and then divides the result by the elementary charge to calculate the total number of electrons. In this case, the coulomb quantity of the dark pulse is obtained by multiplying the area of ​​the digital signal waveform by the physical quantity per unit area and the reciprocal of the conversion coefficient. Then, the total number of electrons in the dark pulse is obtained by dividing the coulomb quantity of the dark pulse by the elementary charge. Since the physical quantity per unit area, the conversion coefficient, and the elementary charge are all constant values, the gain can be easily calculated simply by determining the area of ​​the digital signal waveform.

[0014] The calculation unit can also calculate the total number of electrons for each of multiple dark pulses, or calculate the gain based on the total number of electrons from multiple dark pulses. The total number of electrons can sometimes deviate from the total number of electrons for each dark pulse. Therefore, by calculating the total number of electrons from multiple dark pulses and using these total electron numbers, the accuracy of the gain calculation can be improved.

[0015] The calculation unit can also calculate another gain based on the supply voltage, which is different from the supply voltage to the photomultiplier tube when a dark pulse is generated. In this case, the gain under one supply voltage is used to calculate the gain under the other supply voltage. Therefore, it is possible to calculate the gain under various supply voltages without acquiring a dark pulse. As a result, the calculation of the gain under various supply voltages can be simplified.

[0016] Another aspect of the light detection device of the present invention includes a photomultiplier tube and the above-described computing device.

[0017] Because the optical detection device has the aforementioned computing device, it can suppress the complexity of the circuit structure and calculate the gain of the photomultiplier tube.

[0018] Another aspect of the present invention is a gain calculation method for calculating the gain of a photomultiplier tube. This gain calculation method includes: acquiring a digital signal based on a dark pulse output from the photomultiplier tube in a dark state; and calculating the total number of electrons in the dark pulse based on the digital signal, and calculating the gain based on the total number of electrons.

[0019] In this gain calculation method, a digital signal based on a dark pulse output from a photomultiplier tube in darkness is acquired, and the total number of electrons in the dark pulse is calculated based on this digital signal. When the photomultiplier tube is in darkness, one hot electron is generated, and a dark pulse is produced by multiplying this one hot electron. Therefore, since the total number of electrons in the dark pulse is equivalent to the gain of the photomultiplier tube, the gain can be calculated based on the total number of electrons. In this way, since a dedicated circuit for measuring gain is not required, the complexity of the circuit structure can be suppressed, and the gain of the photomultiplier tube can be calculated.

[0020] The effects of the invention

[0021] According to the present invention, it is possible to suppress the complexity of the circuit structure and calculate the gain of the photomultiplier tube. Attached Figure Description

[0022] Figure 1 This is a schematic structural diagram of a light detection device including a computing unit in one embodiment.

[0023] Figure 2 This is a diagram used to illustrate dark pulses generated from a photomultiplier tube in the dark.

[0024] Figure 3 It is used for explanation Figure 1 The diagram shows the digital signals acquired by the arithmetic unit.

[0025] Figure 4 It is shown Figure 1 The diagram shows the functional structure of the arithmetic unit.

[0026] Figure 5 It is shown Figure 1 A flowchart illustrating the gain calculation method performed by the shown computing device.

[0027] Figure 6 It shows in detail Figure 5 The flowchart for gain calculation processing.

[0028] Figure 7 It is used for explanation Figure 3 The diagram shows the area of ​​the waveform of the digital signal. Detailed Implementation

[0029] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, in the description of the drawings, the same elements are referred to by the same symbols, and repeated descriptions are omitted.

[0030] Reference Figure 1 The general structure of a light detection device including a computing device according to one embodiment will be described. Figure 1This is a schematic structural diagram of a light detection device including a computing unit in one embodiment. Figure 1 The light detection device 1 shown is a device for detecting light. The light detection device 1 includes a photomultiplier tube (PMT) 2, an amplifier 3, an analog-to-digital converter (A / D converter) 4, a computer 5, a computing unit 6, a digital-to-analog converter (DA converter) 7, and a power supply 8.

[0031] The photomultiplier tube 2 is a structure that converts incident light into a current signal. The photomultiplier tube 2 includes a photoelectric surface 21, an electron multiplier section 22, and an anode 23 (see [link to documentation]). Figure 2 The photoelectric surface 21 is a component (cathode) that converts incident light into photoelectrons. The photoelectric surface 21 generates photoelectrons corresponding to the amount of incident light and emits them to the electron multiplier 22. In the dark, the photoelectric surface 21 generates thermionic electrons and emits them to the electron multiplier 22. The "dark" state refers to a state where incident light, such as the measurement light and background light, is blocked.

[0032] The electron multiplier section 22 is a section that multiplies photoelectrons and thermionic electrons emitted from the photoelectric surface 21. The electron multiplier section 22 includes multiple multiplier electrodes. In this embodiment, the electron multiplier section 22 includes n multiplier electrodes (multiplier electrodes Dy1 to Dyn). Multiplier electrodes Dy1 to Dyn are arranged sequentially from the photoelectric surface 21 toward the anode 23 in multiple stages. Multiplier electrode Dy1 emits secondary electrons through collisions with photoelectrons or thermionic electrons emitted from the photoelectric surface 21. Thus, photoelectrons or thermionic electrons are multiplied. Multiplier electrode Dy1 emits secondary electrons along with photoelectrons or thermionic electrons to multiplier electrode Dy2. Subsequently, each multiplier electrode from Dy2 to Dyn-1 multiplies the electrons emitted from the preceding multiplier electrode and emits the multiplied electrons to the following multiplier electrode. The final multiplier electrode Dyn emits the multiplied electrons to the anode 23. The anode 23 collects electrons multiplied in the electron multiplier section 22 and outputs the collected electrons as a current signal to the outside of the photomultiplier tube 2. The current signal is an analog signal.

[0033] Amplifier 3 is a circuit that converts the current signal output from photomultiplier tube 2 into a voltage signal. The voltage signal is an analog signal. Amplifier 3 uses a conversion factor A. cv The current signal is converted into a voltage signal. Amplifier 3 outputs the voltage signal to A / D converter 4.

[0034] The AD converter 4 is a circuit that converts the voltage signal output from amplifier 3 into a digital signal. The AD converter 4 operates at a sampling frequency f... sThe voltage signal is sampled, and the sampled voltage signal is quantized with a quantized amplitude Δd to generate a digital signal. The AD converter 4 outputs the digital signal to the arithmetic unit 6.

[0035] Computer 5 sets the values ​​of various parameters in the processing unit 6. Examples of parameters include those used for setting the action mode and the conversion coefficient A. cv Sampling frequency f s The parameters for setting the operating mode include the quantization amplitude Δd and the voltage value supplied to the photomultiplier tube 2. Among the parameters for setting the operating mode are values ​​indicating the operating mode of the light detection device 1. The operating modes include: a light detection mode where the light detection device 1 performs normal light detection; and a gain calculation mode where the light detection device 1 measures (calculates) the gain of the photomultiplier tube 2.

[0036] The arithmetic unit 6 is a device that performs calculations using the digital signals output from the AD converter 4. The arithmetic unit 6 may be configured as a circuit including a processor, memory, and a communication module. Examples of processors include microcomputers and CPUs (Central Processing Units). Alternatively, an FPGA (Field Programmable Gate Array) may be used instead of a processor.

[0037] The arithmetic unit 6 performs calculations corresponding to the operating mode set by the computer 5. When the operating mode is set to light detection mode, the arithmetic unit 6 calculates the incident light quantity based on the digital signal output from the AD converter 4. When the operating mode is set to gain calculation mode, the arithmetic unit 6 calculates the gain of the photomultiplier tube 2 based on the digital signal output from the AD converter 4. The arithmetic unit 6 outputs a control voltage corresponding to the supply voltage value set by the computer 5 to the power supply 8 via the DA converter 7. The control voltage is the voltage used to supply the supply voltage with that value to the power supply 8. The functional structure of the arithmetic unit 6 will be described later.

[0038] Power supply 8 is a device that applies a supply voltage to photomultiplier tube 2. Power supply 8 receives a control voltage via DA converter 7 and applies a supply voltage corresponding to the control voltage to photomultiplier tube 2. Power supply 8 is, for example, a high-voltage power supply.

[0039] In addition, the PMT module 10 is composed of a photomultiplier tube 2, an amplifier 3, and a power supply 8.

[0040] Next, refer to Figure 2 and Figure 3 The operation of the optical detection device 1 in the gain calculation mode will be explained. Figure 2This is a diagram used to illustrate dark pulses generated from a photomultiplier tube in the dark. Figure 3 It is used for explanation Figure 1 The diagram shows the digital signals acquired by the arithmetic unit. (See diagram for example.) Figure 2 As shown, when the light detection device 1 operates in gain calculation mode, the photomultiplier tube 2 is in a dark state where the incident light is blocked. The photomultiplier tube 2 is, for example, placed in a darkroom. The PMT module 10 may have a light-shielding function for the photomultiplier tube 2 (light-shielding structure), or the entire PMT module 10 may be placed in darkness. Even when the photomultiplier tube 2 is in darkness, thermionic electrons (dark current) are generated from the photoelectric surface 21. These thermionic electrons are multiplied in the electron multiplier section 22, and the multiplied thermionic electrons are output from the anode 23 as an anode current. Because this anode current has a pulsed waveform, it is called a dark pulse.

[0041] like Figure 3 As shown, the dark pulse I generated in photomultiplier tube 2 dark Converted to voltage signal V by amplifier 3 dark Then, the voltage signal V dark The signal is converted into a digital signal s(t) by the AD converter 4, and the digital signal s(t) is output to the arithmetic unit 6. The arithmetic unit 6 calculates the gain of the photomultiplier tube 2 based on the digital signal s(t). The method for calculating the gain will be described later.

[0042] Next, refer to Figure 4 The functional structure of the arithmetic unit 6 is explained. Figure 4 It is shown Figure 1 The diagram shows the functional structure of the arithmetic unit. Figure 4 As shown, the arithmetic unit 6 functionally includes an acquisition unit 61, an acquisition unit 62, a calculation unit 63, a storage unit 64, and an output unit 65. Since the functions (operations) of each functional unit are explained in detail in the following description of the gain calculation method, the functions of each functional unit will be briefly explained here.

[0043] The acquisition unit 61 is a functional unit that acquires the values ​​of various parameters from the computer 5. For example, the acquisition unit 61 acquires parameters used for setting the action mode, such as the conversion coefficient A. cv Sampling frequency f s The quantization amplitude Δd and the voltage value supplied to the photomultiplier tube 2.

[0044] The acquisition unit 62 is a functional unit that acquires digital signals from the AD converter 4. When the operating mode is set to light detection mode, the acquisition unit 62 acquires the digital signal corresponding to the incident light. When the operating mode is set to gain calculation mode, the acquisition unit 62 acquires the digital signal based on the dark pulse generated by the thermionic multiplication in the photomultiplier tube 2.

[0045] The calculation unit 63 is a functional unit that performs various calculations. When the operating mode is set to light detection mode, the calculation unit 63 calculates the incident light quantity based on the digital signal. When the operating mode is set to gain calculation mode, the calculation unit 63 calculates the total number of electrons in the dark pulse based on the digital signal, and calculates the gain of the photomultiplier tube 2 based on the total number of electrons. The calculation unit 63 can also calculate the gain of the photomultiplier tube 2 based on the estimated gain of one dark pulse as the estimated gain, and calculate the gain of the photomultiplier tube 2 based on the estimated gain of multiple dark pulses. The estimated gain is the gain calculated from one dark pulse (digital signal), and is also called the electron multiplication rate. On the other hand, the gain of the photomultiplier tube 2 obtained from the average value calculated based on the estimated gain (electron multiplication rate) of multiple dark pulses is also called the current multiplication rate.

[0046] Storage unit 64 is a functional unit that stores (accommodates) the estimated gain. Storage unit 64 stores the estimated gain calculated by calculation unit 63.

[0047] Output unit 65 is a functional unit that outputs the calculation results of calculation unit 63. When the operating mode is set to light detection mode, output unit 65 outputs the incident light quantity. When the operating mode is set to gain calculation mode, output unit 65 outputs the gain of photomultiplier tube 2. Output unit 65 outputs control voltage to power supply 8 via DA converter 7.

[0048] Next, refer to Figures 5-7 The method for calculating the gain of the arithmetic unit 6 is explained. Figure 5 It is shown Figure 1 A flowchart illustrating the gain calculation method performed by the shown computing device. Figure 6 It shows in detail Figure 5 The flowchart for gain calculation processing. Figure 7 It is used for explanation Figure 3 The diagram shows the area of ​​the waveform of the digital signal. Figure 5 The series of processes shown begins, for example, by setting the operating mode to gain calculation mode. Furthermore, as described above, photomultiplier tube 2 is in a dark state.

[0049] like Figure 5 As shown, firstly, the acquisition unit 61 acquires the values ​​of each parameter (step S11). In step S11, the acquisition unit 61 acquires the conversion coefficient A. cv Sampling frequency f s The quantization amplitude Δd and the voltage value supplied to the photomultiplier tube 2 are then measured. The acquisition unit 61 then obtains the conversion coefficient A. cv Sampling frequency f s The quantized amplitude Δd is output to the calculation unit 63, and the control voltage corresponding to the voltage value is output to the output unit 65.

[0050] As described above, thermionic electrons are generated from the photoelectric surface 21. These thermionic electrons are multiplied in the electron multiplier 22, and a dark pulse I is output from the anode 23. dark Then, dark pulse I dark Converted to voltage signal V by amplifier 3 dark Then, in AD converter 4, at a sampling frequency f... s For voltage signal V dark Sampling is performed on the sampled voltage signal V. dark The signal is quantized by a quantized amplitude Δd, thereby generating a digital signal s(t). The digital signal s(t) is then input to the arithmetic unit 6. That is, the digital signal s(t) is input to the arithmetic unit 6 as a discrete digital value. Time t is discrete time and increases by 1 for each sampling time (=1 / fs).

[0051] Next, the acquisition unit 62 acquires data based on the dark pulse I. dark The digital signal s(t) is then obtained (step S12). The acquisition unit 62 then outputs the digital signal s(t) to the calculation unit 63.

[0052] Next, gain calculation is performed (step S13). In step S13, as follows... Figure 6 As shown, the calculation unit 63 first measures the area S of the waveform of the digital signal s(t). total [Unit: count] (Step S31). For example... Figure 7 As shown, in this embodiment, the digital signal s(t) has a pulse-like waveform from start time a to end time b. As shown in equation (1), the area S... total The area S is calculated by summing the numerical values ​​from start time a to end time b. The calculation unit 63 uses formula (1) to calculate (measure) the area S. total .

[0053]

[0054] Next, the calculation unit 63 calculates the voltage signal V. dark The signal quantity [unit: V·s] (step S32). As shown in equation (2), the physical quantity Δs [unit: V·s / count] of each unit bit (unit area) of the digital value is divided by the quantized amplitude Δd [unit: V / count] by the sampling frequency f. s [Unit: Hz] is used to calculate.

[0055]

[0056] As shown in equation (3), the voltage signal V dark The signal quantity will be transferred through the area S totalThe result is obtained by multiplying the physical quantity Δs. The calculation unit 63 uses equation (3) to calculate the voltage signal V. dark The signal quantity. Furthermore, for ease of explanation, the voltage signal V is included in the equation. dark The semaphore is represented as "V" dark The situation of "".

[0057]

[0058] Next, the calculation unit 63 calculates the dark pulse I. dark The current quantity [unit: A·s] (step S33). Since amplifier 3 converts the current signal into a voltage signal, by using this inverse conversion, the voltage signal V is obtained. dark Find the dark pulse I from the signal quantity dark The current quantity. Specifically, as shown in equation (4), the dark pulse I dark The current quantity is transmitted through the voltage signal V. dark Signal quantity and conversion coefficient A cv The result is obtained by multiplying the reciprocals of [unit: V / A]. The calculation unit 63 uses equation (4) to calculate the dark pulse I. dark The current quantity. Furthermore, for ease of explanation, the dark pulse I is included in the equation. dark The current quantity is expressed as "I". dark The situation of "".

[0059]

[0060] Next, the calculation unit 63 calculates the dark pulse I. dark The coulomb quantity [unit: C] (step S34). Generally, 1 coulomb [C] is defined as the amount of charge transported when a current of 1 ampere [A] flows for 1 second [s]. Therefore, 1 [A·s] can be replaced by 1 [C]. Therefore, as shown in equation (5), the dark pulse I dark The coulomb quantity is the same as that of the dark pulse I. dark The current is the same value. The calculation unit 63 uses equation (5) to calculate the dark pulse I. dark Coulomb quantity.

[0061]

[0062] Next, the calculation unit 63 calculates the dark pulse I. dark Total number of electrons D electron [Unit: electrons] (Step S35). Generally, the charge [C] of each electron is called the elementary charge e. Therefore, as shown in equation (6), the total number of electrons D electron Through dark pulse I dark The coulomb quantity is obtained by dividing the elementary charge e. The total number of electrons D is calculated using equation (6) in calculation section 63. electronThat is, the calculation unit 63 calculates the area S of the waveform of the digital signal s(t) total , and the physical quantity Δs per unit bit (unit area) obtained by dividing the quantization amplitude Δd by the sampling frequency f s and the reciprocal of the conversion coefficient A cv are multiplied by the area S total , and the total number of electrons D is calculated by dividing the multiplication result by the elementary charge e electron .

[0063]

[0064] Next, the calculation unit 63 calculates the estimated gain μ [unit: times] (step S36). As shown in equation (7), the total number of electrons D electron is obtained by multiplying the number K of electrons incident from the photocathode 21 (cathode) to the first dynode Dy1 electron [unit: piece] and the estimated gain μ.

[0065] D etectron =K etectron ×μ [piece] (7)

[0066] Here, the dark pulse is mainly caused by thermoelectrons from the photocathode 21. Dark pulses occur discretely, and in most cases, they are generated originating from one thermoelectron. Accordingly, equation (7) can be simplified to equation (8).

[0067] D etectron =μ [piece] (8)

[0068] Equation (8) shows that the total number of electrons D under an environment where thermoelectrons can be measured (state in darkness) electron and the estimated gain μ are the same value. Therefore, by swapping the right side and the left side of equation (8), equation (9) is obtained. The calculation unit 63 calculates the estimated gain μ using equation (9).

[0069]

[0070] Through the above, the gain calculation processing ends. Furthermore, the calculation unit 63 stores the estimated gain μ in the storage unit 64 (step S14).

[0071] Next, the calculation unit 63 determines whether to end the measurement (step S15). In step S15, the calculation unit 63 determines that the measurement is not ended when the estimated gains μ of the preset number of calculation times have not been calculated. The calculation unit 63 determines that the measurement is ended when the estimated gains μ of the above number of calculation times have been calculated. The number of calculation times is set to, for example, about 1000 times. In step S15, when it is determined that the measurement is not ended (step S15; No), steps S12 to S15 are performed again.

[0072] On the other hand, in step S15, if it is determined that the measurement is to end (step S15; Yes), the calculation unit 63 reads the estimated gain μ of the number of calculations from the storage unit 64, and calculates the average value of the estimated gain μ of the number of calculations (step S16). Then, the calculation unit 63 outputs the average value as the gain of the photomultiplier tube 2 to the output unit 65.

[0073] Next, if the output unit 65 receives a gain from the calculation unit 63, it outputs the gain to the outside of the arithmetic device 6 (step S17). For example, the output unit 65 outputs the gain along with the voltage value of the supplied voltage to the computer 5. Then, the computer 5 establishes a correspondence between the voltage value of the supplied voltage and the gain and stores it.

[0074] The above steps complete the series of processes for calculating the gain. Furthermore, since the estimated gain μ is obtained from equation (9), if the measured area S... total If so, the estimated gain μ can be calculated. Therefore, steps S32 to S35 can also be omitted. At least a portion of step S11 can also be performed before the operation mode is set to gain calculation mode.

[0075] For example, as a measurement condition, assume the sampling frequency f s The setting is 100 MSPS (Mega-sample(s) per second), the quantization amplitude Δd is set to 0.1 mV / count, and the conversion factor A is... cv The value is set to 0.1 V / μA. The area S of the waveform of the digital signal s(t) observed under these measurement conditions is... total Set to 1×10 5 count. According to equation (3), the voltage signal V dark The semaphore is calculated as 1×10 -7 V·s(=1×10 5 ×{1 / (100×10 6 )}×(0.1×10 -3 )).

[0076] Furthermore, according to equation (4), the dark pulse I dark The current is calculated as 1×10 -12 A·s(=1×10 -7 ×10×10 -6 As mentioned above, since 1[C] equals 1[A·s], therefore the dark pulse I dark The coulomb quantity is 1×10 -12 C. Since the elementary charge e is 1.602 × 10 -19 C, therefore according to equation (6), the number of electrons D electronThe calculation is 6.24 × 10 6 (≒(1×10)) -12 ) / (1.602×10 -19 6.24 × 10⁻⁶ electrons are produced from one hot electron. 6 Therefore, the estimated gain μ is 6.24 × 10⁻⁶ electrons. 6 .

[0077] The above calculations are performed on digital signals s(t) with waveforms greater than 1000. The average value of the estimated gain μ obtained from these calculations is set as the gain of photomultiplier tube 2.

[0078] Next, the operation of the arithmetic unit 6 when the operation mode is set to light detection mode will be briefly explained. First, the acquisition unit 61 acquires the conversion coefficient A from the computer 5 as a parameter value. cv Sampling frequency f s The quantization amplitude Δd, the voltage value supplied to the photomultiplier tube 2, and the gain corresponding to that voltage value are then obtained. The acquisition unit 61 then converts the conversion coefficient A... cv Sampling frequency f s The quantized amplitude Δd and gain are output to the calculation unit 63, and the control voltage corresponding to the voltage value is output to the output unit 65.

[0079] Then, the acquisition unit 62 acquires the digital signal s(t) based on the incident light and outputs the digital signal s(t) to the calculation unit 63. Then, the calculation unit 63 uses the conversion coefficient A cv Sampling frequency f s The incident light quantity is calculated from the digital signal s(t) by quantizing the amplitude Δd and the gain, and then output to the output unit 65. The output unit 65 then outputs the incident light quantity to the outside of the arithmetic unit 6. This completes the series of processes in the light detection mode.

[0080] In the light detection device 1, the arithmetic device 6, and the gain calculation method described above, the dark pulse I output from the photomultiplier tube 2 in a dark state is obtained. dark Given a digital signal s(t), calculate the dark pulse I based on this digital signal s(t). dark Total number of electrons D electron When photomultiplier tube 2 is in darkness, one hot electron is generated. Multiplying this hot electron can produce a dark pulse I. dark Therefore, due to the dark pulse I dark Total number of electrons D electron This is equivalent to the estimated gain μ, and therefore can be based on the total number of electrons D. electron Calculate the gain of photomultiplier tube 2.

[0081] As described above, most of the parameter values ​​used to calculate the incident light quantity from the digital signal s(t) are constant, but the gain can vary depending on the surrounding environment and usage conditions of the photomultiplier tube 2. A measurement circuit for determining the gain is considered, but this could complicate the circuit structure. A structure for stabilizing the gain is also considered, but this could increase the size of the photomultiplier tube 2. A reference light source is also considered, but high stability of the reference light source would require increasing the size of the light detection device 1. In the light detection device 1, the arithmetic unit 6, and the gain calculation method, since a dedicated circuit for measuring the gain, a gain stabilization structure, and a reference light source are not required, the complexity of the circuit structure can be suppressed, and the gain of the photomultiplier tube 2 can be calculated.

[0082] The digital signal s(t) acquired by the arithmetic unit 6 is processed by the A / D converter 4 at a sampling frequency f s The conversion factor A will be used through amplifier 3. cv For dark pulse I dark The voltage signal V obtained by current-to-voltage conversion dark It is generated through quantization. The computing unit 63 is based on the digital signal s(t) and the conversion coefficient A. cv and sampling frequency f s Calculate the total number of electrons D electron According to this structure, considering the conversion coefficient A used to generate the digital signal s(t) cv and sampling frequency f s Therefore, it can increase the total number of electrons D. electron The calculation accuracy is improved. As a result, the accuracy of gain calculation can be increased.

[0083] Specifically, by measuring the area S of the waveform of the digital signal s(t) total With physical quantity Δs and conversion coefficient A cv Multiplying the reciprocals of the terms yields the dark pulse I. dark The coulomb quantity. Then, through the dark pulse I. dark The dark pulse I is obtained by dividing the coulomb quantity by the elementary charge e. dark Total number of electrons D electron Due to the physical quantity Δs and the conversion coefficient A cv Since the elementary charge e is a constant, only the area S needs to be calculated. total The gain can be easily calculated.

[0084] According to each dark pulse I dark Total number of electrons D electron Sometimes deviations occur. In contrast, the calculation unit 63 performs a predetermined number of calculations on the dark pulses I. dark The total number of electrons D calculated by each method electron And based on these total electron numbers Delectron Calculate the gain. Specifically, the calculation unit 63 will calculate the gain from each dark pulse I. dark The average value of the estimated gain μ is used as the gain calculation for photomultiplier tube 2. In other words, the calculation unit 63 calculates the number of dark pulses I. dark Total number of electrons D electron The average value is used as the gain of photomultiplier tube 2. Thus, by using multiple dark pulses I... dark Total number of electrons D electron This can improve the accuracy of gain calculation.

[0085] Furthermore, the optical detection device of the present invention is not limited to the embodiments described above.

[0086] The values ​​of each parameter can also be set from an external computer. In this case, the light detection device 1 may not have a computer 5. The photomultiplier tube 2 can also receive a supply voltage from an external power source. In this case, the light detection device 1 may not have a DA converter 7 and a power supply 8.

[0087] In the above embodiment, the calculation unit 63 uses the average value of the estimated gain obtained from multiple dark pulses as the gain of the photomultiplier tube 2, but the method for calculating the gain of the photomultiplier tube 2 is not limited to this. For example, the calculation unit 63 may also use the estimated gain obtained from one dark pulse as the gain of the photomultiplier tube 2. The calculation unit 63 may also calculate the gain of the photomultiplier tube 2 using the median value of the estimated gain obtained from multiple dark pulses.

[0088] The calculation unit 63 can also calculate the gain under another supply voltage based on the gain calculated for one supply voltage. The other supply voltage is a supply voltage that is different from the supply voltage to the photomultiplier tube 2 when generating a dark pulse in the gain calculation mode. As shown in equation (10), the gain of the photomultiplier tube 2 can be represented by a constant A, the voltage value V of the supply voltage, and the value kn. The value kn is a value determined by the structure of the photomultiplier tube 2.

[0089] Gain = A × V kn (10)

[0090] For example, the relationship between supply voltage and gain, when depicted using a double logarithmic curve, becomes a straight line with a slope equal to the value kn. Therefore, according to equation (10), the gain under one supply voltage can be calculated using the gain under another supply voltage. Thus, the gain under various supply voltages can be calculated without acquiring dark pulses. As a result, the calculation of the gain under various supply voltages can be simplified.

[0091] The arithmetic unit 6 can also calculate the gain for each of the multiple supply voltages using the gain calculation method described above.

[0092] The light detection device 1 may also include a light source (e.g., a single-photon light source) capable of outputting a specified amount of weak light. In this case, the weak light can be irradiated onto the photoelectric surface 21 from the light source, thereby allowing the processing unit 6 to acquire the digital signal of the weak light from the light source along with the digital signal based on dark pulses, and to calculate the gain based on these digital signals. Alternatively, the light detection device 1 may not include the aforementioned light source, or an external light source may be used for gain calculation.

[0093] Explanation of symbols

[0094] 1…light detection device, 2…photomultiplier tube, 3…amplifier, 4…AD converter, 5…computer, 6…computing unit, 7…DA converter, 8…power supply, 21…photoelectric surface, 22…electron multiplier, 23…anode, 61…acquisition unit, 62…acquisition unit, 63…computing unit, 64…storage unit, 65…output unit.

Claims

1. A computing device, wherein, It is a computational device for calculating the gain of a photomultiplier tube. have: The acquisition unit acquires a digital signal based on a dark pulse output from the photomultiplier tube in a dark state; and The computing unit calculates the total number of electrons in the dark pulse based on the digital signal, and calculates the gain based on the total number of electrons.

2. The computing device according to claim 1, wherein, The digital signal is generated by quantizing the voltage signal obtained by converting the dark pulse into a current-to-voltage signal using an amplifier and conversion coefficients at a sampling frequency via an AD converter. The calculation unit calculates the total number of electrons based on the digital signal, the conversion coefficient, and the sampling frequency.

3. The computing device according to claim 2, wherein, The computing unit calculates the area of ​​the waveform of the digital signal, multiplies the physical quantity per unit area obtained by dividing the quantized amplitude of the AD converter by the sampling frequency and the reciprocal of the conversion coefficient by the area, and calculates the total number of electrons by dividing the result of the multiplication by the elementary charge.

4. The arithmetic device according to any one of claims 1 to 3, wherein, The calculation unit calculates the total number of electrons for each of the plurality of dark pulses, and calculates the gain based on the total number of electrons for the plurality of dark pulses.

5. The arithmetic device according to any one of claims 1 to 4, wherein, The calculation unit calculates another gain based on the gain, under a supply voltage different from the supply voltage to the photomultiplier tube when the dark pulse is generated.

6. A light detection device, wherein, have: The photomultiplier tube; and The arithmetic device according to any one of claims 1 to 5.

7. A gain calculation method, wherein, This is a gain calculation method for calculating the gain of a photomultiplier tube. include: The step of acquiring a digital signal based on a dark pulse output from the photomultiplier tube in a dark state; and The steps of calculating the total number of electrons in the dark pulse based on the digital signal, and calculating the gain based on the total number of electrons.

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