JP2006017550A - Circuit for photodetection, and photodetector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit for photodetection, and a photodetector capable of measuring a quantity of light over a wide dynamic range by using a PMT. <P>SOLUTION: The circuit 2 for photodetection is provided with a voltage application means 21 for apply a predetermined potential gradient to a photocathode 33 and n stages of dynodes Dy<SB>1</SB>-Dy<SB>n</SB>, and a first changeover means 23 for switching the potential gradient between the dynode Dy<SB>1</SB>and the dynode Dy<SB>2</SB>over to a potential gradient reverse to it. With respect to light to be detected L having a smaller light quantity, the switching means SW<SB>1</SB>of the changeover means 23 is turned disconnected. On this occasion, secondary electron multiplication of photoelectrons generated at the photocathode 33 is performed by the dynodes Dy<SB>1</SB>-Dy<SB>n</SB>, and an output current I<SB>1</SB>is taken out from an anode 37. With respect to light to be detected L having a larger light quantity, the switch SW<SB>1</SB>is turned connected. On this occasion, photoelectrons generated at the photocathode 33 are taken out from the dynode Dy<SB>1</SB>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photodetector circuit and a photodetector connected to a photomultiplier tube.

  In recent years, when detecting light using a photomultiplier tube (hereinafter referred to as PMT), it has been required to measure the light amount with a wider dynamic range (that is, the ratio between the minimum light amount and the maximum light amount that can be detected). It has been. As a method of expanding the dynamic range, for example, there is a method of controlling the potential gradient applied to each dynode of the PMT. However, since it is necessary to maintain the linearity of the output current with respect to the incident light quantity, there is a limit to the control by the potential gradient.

On the other hand, as a device for realizing a wider dynamic range, for example, there is a light detection device disclosed in Patent Document 1. This device includes two amplifiers (I / V conversion circuit), one amplifier is connected to the anode of the PMT and the other amplifier is connected to the final stage dynode of the PMT. The amplifier from which the output signal is used is controlled according to the amount of light incident on the PMT. Since the output current from the last stage dynode is smaller than the output current from the anode, this apparatus attempts to expand the dynamic range by extracting the output current from the last stage dynode instead of the anode when the amount of incident light is large.
JP-A-9-61537

  In the apparatus disclosed in Patent Document 1, the expansion width of the dynamic range is limited to a width corresponding to the electron multiplication factor of the final stage dynode. Patent Document 1 states that a current generated in an arbitrary dynode provided before the final stage may be detected. However, in this device configuration, each dynode multiplies the electrons received from the previous stage and emits them to the subsequent stage, so even if the current is taken out from the dynode on the way, if the incident light quantity is large, The flowing current exceeds the maximum rating of the PMT.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a light detection circuit and a light detector that can measure a light amount with a wider dynamic range using a PMT.

  In order to solve the above-described problems, a first photodetection circuit according to the present invention includes a photocathode that emits photoelectrons corresponding to the amount of incident light and dynodes arranged in n stages (n is an integer of 2 or more). Is a photodetection circuit connected to a photomultiplier tube having a multiplication unit for multiplying and an anode for collecting electrons multiplied by the multiplication unit. Voltage applying means for providing a potential gradient of the mth stage, and when taking out electrons from the mth stage (1 ≦ m ≦ n−1) dynodes of the nth dynodes, And a first switching means for switching the potential gradient between the dynode to a potential gradient opposite to the predetermined potential gradient.

  When the first switching means has not switched the potential gradient between the m-th dynode and the (m + 1) -th dynode, a predetermined potential gradient is applied to each of the n-stage dynodes of the multiplication unit. Thus, the photoelectrons generated at the photocathode are multiplied by secondary electrons at the n-stage dynode and collected at the anode. Therefore, for a small amount of incident light, a large electron multiplication factor can be realized by n stages of dynodes. On the other hand, when the first switching means switches the potential gradient between the m-th stage dynode and the m + 1-th stage dynode to the reverse slope, the m-th stage dynode to the m + 1-th stage dynode. Secondary electron emission is suppressed, and a current corresponding to the amount of incident light can be extracted from the m-th stage dynode. Therefore, for a large amount of incident light, a small electron multiplication factor can be realized by m-1 stage dynodes smaller than n stages. In particular, when m = 1, photoelectrons generated at the photocathode can be taken out from the first dynode without multiplication. From the above, according to the above-described light detection circuit, it is possible to measure the amount of light using a PMT with a wider dynamic range than the conventional apparatus.

  The light detection circuit may further include a control unit that controls the first switching unit based on the amount of current from the anode and the amount of current from the m-th dynode. Thereby, the electron multiplication factor in the PMT can be automatically set according to the amount of light incident on the photocathode.

  The photodetection circuit may be characterized in that the voltage application means includes a Zener diode that forms a potential gradient between the photocathode and the m-th dynode. Thereby, compared with the case where the potential gradient between the photocathode and the m-th dynode is formed using a resistance element, the influence on the potential gradient caused by the current taken out from the m-th dynode is suppressed. be able to.

  The light detection circuit may further include second switching means for switching the potentials of the dynodes after the (m + 2) th stage so as to be substantially the same potential as that of the mth stage dynode. Thereby, the emission of secondary electrons from the m-th dynode is almost completely suppressed.

  The photodetector according to the present invention includes a photocathode that emits photoelectrons according to the amount of incident light, a dynode arranged in n stages (n is an integer of 2 or more), a multiplier that multiplies photoelectrons, and a multiplier. A photomultiplier having an anode for collecting the electrons multiplied by the photodetection circuit and the photodetection circuit according to claim 1. As a result, a photodetector capable of measuring the amount of light with a wider dynamic range than before can be provided.

  According to the light detection circuit and the light detector of the present invention, the light quantity can be measured with a wide dynamic range using the PMT.

  Embodiments of a photodetection circuit and a photodetector according to the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
A first embodiment of a light detection circuit and a light detector according to the present invention will be described. FIG. 1 is a circuit diagram showing the configuration of the photodetector 1 and the light detection circuit 2 according to the present embodiment. Referring to FIG. 1, the photodetector 1 includes a PMT 3 and a light detection circuit 2.

The PMT 3 includes a photocathode 33 that emits photoelectrons corresponding to the amount of incident light L to be detected, a multiplier 35 that multiplies photoelectrons, and an anode 37 that collects the electrons multiplied by the multiplier 35. It is inside the vacuum tube 39. Multiplication unit 35, an n-stage (n is an integer of 2 or more) have to arranged the first stage dynode Dy ₁ through n-th stage (final stage) dynode Dy _n. Dynodes Dy ₁ is disposed at a position for receiving the photoelectrons from the photocathode 33, the dynodes Dy ₂ ~Dy _n is arranged in a position for receiving the secondary electrons from the preceding dynode. The anode 37 is disposed at a position for receiving the secondary electrons from the dynode Dy _n.

The light detection circuit 2 includes a voltage application unit 21 and a first switching unit 23. Voltage applying means 21 is a means for providing a predetermined potential gradient in the dynode _Dy 1 _{~Dy n} photocathode 33 and n stages. In the present embodiment, the voltage application unit 21 includes a first voltage application unit 21a and a second voltage application unit 21b. First voltage applying means 21a includes a Zener diode _{D 1} and the resistor element _{R 3.} The anode side of the Zener diode D ₁ is connected to the power supply terminal 17 via the resistance element R ₁ and is also connected to the photocathode 33. Cathode of the Zener diode D ₁ is connected to one end of the resistance element R _3. The other end of the resistance element R ₃ is connected to the reference potential line 38. A dynode Dy ₁ is connected between the Zener diode D ₁ and the resistance element R ₃ via the resistance element R ₂ . The power supply terminal 17 is supplied with a power supply voltage HV (<0). With this configuration, the photocathode 33 is supplied with the potential V _k , and the dynode Dy ₁ is supplied with the potential V ₁ (> V _k ) divided by the Zener diode D ₁ and the resistance element R ₃ .

Second voltage applying means 21b has a resistance element _Rd 1 ~ Rd _n. Resistance element _Rd 1 ~ Rd _n are connected in series between the resistor element _{R 1} and the reference potential line 31. One end of the resistance element Rd ₁ is connected to the power supply terminal 17 via the resistance element R ₁ . One end of the resistive element Rd _n is connected to the reference potential line 31. Between adjacent resistive elements to each other among the resistive element _Rd 1 ~ Rd _n, are respectively connected to dynodes _Dy 2 _{~Dy n.} Second voltage applying means 21b, by dividing the supply voltage HV by the resistor element _Rd 1 ~ Rd _n, generates a potential _V 2 ~V _n giving the dynode _Dy 2 _{~Dy n.} At this time, the second voltage application means 21b generates a potential V ₂ ~V _n such that the higher potential as the subsequent dynodes. The second voltage applying unit 21b, as in the potential _{V 2} of the dynode Dy ₂ is higher than the potential _{V 1} of the dynode Dy _1, it generates each potential _V 2 ~V _n.

First switching means 23, of the dynode Dy ₁ ～Dy _n of n stages, with means for switching the reverse potential gradient is a predetermined potential gradient potential gradient between the dynode Dy ₁ and dynode Dy ₂ is there. In the present embodiment, the first switching means 23 comprises a switch means SW _1. One end of the switch means SW ₁ is connected to the dynode Dy ₁ via the resistance element R _2, and the other end of the switch means SW ₁ is connected to the reference potential line 40. When the switch means SW ₁ is short-circuited, the potential _{V 1} of the dynode Dy ₁ becomes the reference potential which is higher than the potential _{V 2} of the dynode Dy _2, the potential gradient is reversed between the dynode Dy ₁ and dynode Dy ₂ Will be. At this time, the magnitude of the power supply voltage HV supplied to the power supply terminal 17 may be appropriately reduced. As the switch means SW ₁ , an electrical switch such as a transistor can be used in addition to a mechanical switch.

The light detection circuit 2 includes wirings 25 and 28. The wiring 25 is a means for taking out the output current I ₂ from the dynode Dy ₁ . One end of the wiring 25 is connected between the dynodes Dy ₁ and the resistance element R _2, the other end of the wiring 25 is connected to the output terminal 27b. The wiring 28 is a means for taking out the output current I ₁ from the anode 37. One end of the wiring 28 is connected to the anode 37, and the other end of the wiring 28 is connected to the output terminal 27a. Incidentally, the anode 37, the dynode Dy _n of the potential _V higher than the _n potential _{V P} (e.g. reference potential) is applied.

A specific numerical example in the light detection circuit 2 of the present embodiment is as follows.
Power supply voltage HV: -1100 V or -400 V (switch means SW ₁ short-circuited: -200 V)
Resistance element R ₁ : 100 kΩ
Resistance element R ₂ : 10 kΩ
Resistance element R ₃ : 2 MΩ
Resistance element Rd ₁ : 1.5 MΩ
Resistive element _Rd 2 _~Rd n: _500kΩ

The photodetector 1 and the photodetection circuit 2 having the above configuration operate as follows. When the detection light L enters the photocathode 33 of the PMT 3, photoelectrons corresponding to the amount of incident light are generated at the photocathode 33. If the amount of incident light is small, it sets the switch means SW ₁ of the first switching means 23 to the disconnected state. The setting of the connection state / non-connection state of the switch means SW ₁ may be performed manually may be performed automatically on the basis of the amount of incident light. At this time, each of the photocathode 33 and the dynode _Dy 1 _{~Dy n,} the potential _V k of a predetermined potential gradient by the voltage applying means _21, since V 1 ~V _n are given, generated in the photocathode 33 photoelectrons are multiplication secondary electrons are released in order to dynode Dy ₁ ~Dy _n. The multiplied secondary electrons are collected by the anode 37 and output from the anode 37 to become an output current I ₁ , which is provided to the output terminal 27 a via the wiring 28.

Further, when the incident light amount is large, it sets the switch means SW ₁ of the first switching means 23 to the connected state (short circuit). At this time, the potential gradient is reversed between the dynode Dy ₁ and dynode Dy _2, the potential _{V 1} of the dynode Dy ₁ is higher than the potential _{V 2} of the dynode Dy _2. Photoelectrons generated at the photocathode 33 are emitted to the dynode Dy ₁ . The photoelectrons that have reached the dynode Dy ₁ are not emitted to the dynode Dy ₂ due to the reverse potential gradient, and the electrons are not multiplied by the subsequent dynodes. Then, the output current I ₂ is output from the dynode Dy ₁ and provided to the output terminal 27 _b via the wiring 25.

The effects of the photodetector 1 and the light detection circuit 2 according to the present embodiment will be described. In the photodetector 1 and the light detection circuit 2 of the present embodiment, the first switching unit 23 can switch the potential gradient between the dynode Dy ₁ and the dynode Dy ₂ as described above. When the amount of incident light is relatively small, by applying a predetermined potential gradient in each of the dynode Dy ₁ ~Dy _n, it is possible to operate the PMT3 as an ordinary photomultiplier tube. Therefore, since a large electron multiplication factor can be realized with respect to a small incident light amount, the light amount of weak light can be accurately measured. Further, when the amount of incident light is relatively large, by reversing the potential gradient between the dynode Dy ₁ and dynode Dy _2, the secondary electron emission from the dynodes Dy ₁ to dynode Dy ₂ is suppressed. That is, the PMT 3 can be operated as a photoelectric tube that outputs photoelectrons corresponding to the amount of incident light without multiplication. Therefore, it is possible to suitably measure the amount of intense light. From the above, according to the light detector 1 and the light detection circuit 2 according to the present embodiment, it is possible to measure the light amount with a wider dynamic range than the conventional apparatus using the PMT 3.

In addition, as in the present embodiment, the voltage application unit 21 preferably includes a Zener diode D ₁ that forms a potential gradient between the photocathode 33 and the dynode Dy ₁ . Since the Zener voltage of the Zener diode D ₁ is hardly affected by the current, the voltage applying means 21 is configured in this way, so that the dynode Dy ₁ is compared with the case where a potential gradient is formed using a resistance element. They are possible to suppress the influence of the potential gradient due to the output current I ₂ from.

(Second Embodiment)
Next, a second embodiment of the photodetector and the circuit for detecting light according to the present invention will be described. FIG. 2 is a circuit diagram showing configurations of the photodetector 1a and the light detection circuit 2a according to the second embodiment. Referring to FIG. 2, the photodetector 1a includes a PMT 3 and a light detection circuit 2a. Among these, since the configuration of the PMT 3 is the same as that of the first embodiment, detailed description thereof is omitted. The light detection circuit 2a includes a voltage application unit 21, a first switching unit 23, and wirings 25 and 28 having the same configuration as that of the first embodiment.

  In addition to the above configuration, the photodetector 1a and the light detection circuit 2a according to the present embodiment control the first switching unit 23 and the power supply voltage HV based on the amount of light incident on the photocathode 33 (control circuit). 5). Then, the photodetector 1a and the light detection circuit 2a of the present embodiment control the power supply voltage HV so as to obtain a high electron multiplication factor when the detected light L is extremely weak, and measure the amount of incident light. When the intensity of the detected light L is slightly small, the incident light quantity is measured by controlling the power supply voltage HV so that the electron multiplication factor is low. When the intensity of the detected light L is relatively large, the photoelectrons are multiplied. Measure the amount of incident light.

Specifically, the light detection circuit 2a includes a control circuit 5, a high-voltage power supply 7, I / V converters 11a and 11b, and comparators 13a to 13c. I / V converter 11a is a current-voltage converting means for converting an output current I ₂ from the dynode Dy ₁ to the light quantity signal S ₂ is a voltage signal. Input of I / V converter 11a is connected between the dynodes Dy ₁ through the switch means SW ₂ and wiring 25 and the resistance element _{R 2.} The output terminal of the I / V converter 11a is connected to the output terminal 15a. I / V converter 11a via the output terminal 15a to provide a light intensity signal _{S 2} to the outside of the optical detector 1a. Further, I / V converter 11b is a current-voltage converting means for converting the output current I ₁ from the anode 37 to the light amount signals S ₁ is a voltage signal. The input end of the I / V converter 11 b is connected to the anode 37 via the wiring 28. The output terminal of the I / V converter 11b is connected to the output terminal 15b. I / V converter 11b via the output terminal 15b provides a light intensity signals _{S 1} to the outside of the optical detector 1a.

The comparator 13a, based on the light quantity signal S _2, the amount of incident light is a means for determining whether less than a predetermined first amount of light. The predetermined first light amount is a light amount that becomes a threshold value between an operation in which the photodetection circuit 2a outputs photoelectrons without secondary electron multiplication and an operation in which secondary electron multiplication outputs. The positive side input terminal of the comparator 13a is connected to the output terminal of the I / V converter 11a. To the negative input terminal of the comparator 13a, the reference voltage Vr ₂ showing a predetermined first amount of light is supplied. The output terminal of the comparator 13 a is connected to the control circuit 5. The comparator 13a provides a signal indicating whether or not the light quantity signal _{S 2} from the I / V converter 11a is smaller than the reference voltage Vr ₂ to the control circuit 5.

The comparator 13b based on the light quantity signal S _1, the amount of incident light is a means for determining whether greater than a predetermined first amount of light. The plus side input terminal of the comparator 13b is connected to the output terminal of the I / V converter 11b. A reference voltage Vr ₁₁ indicating a predetermined first light quantity is supplied to the negative side input terminal of the comparator 13b. The output terminal of the comparator 13b is connected to the control circuit 5. The comparator 13b provides a signal indicating whether or not the light amount signals _{S 1} from the I / V converter 11b is greater than the reference voltage _{Vr 11} to the control circuit 5. Further, the comparator 13c, based on the light quantity signal S _1, a means for determining the magnitude of the incident light quantity and the predetermined second amount of light. The predetermined second light amount is a light amount serving as a threshold when the secondary electron multiplication factor in the PMT 3 is switched by controlling the power supply voltage HV (<0) to the PMT 3. The positive side input terminal of the comparator 13c is connected to the output terminal of the I / V converter 11b. To the negative input terminal of the comparator 13c, the reference voltage Vr ₁₂ indicating a predetermined second amount of light is supplied. The output terminal of the comparator 13 c is connected to the control circuit 5. The comparator 13c provides a signal indicative of the magnitude relation between the light quantity signals _{S 1} and the reference voltage _{Vr 12} from the I / V converter 11b to the control circuit 5.

The control circuit 5 is a control unit that controls the first switching unit 23 and the power supply voltage HV based on the amount of light incident on the photocathode 33. In the present embodiment, the control circuit 5 controls the first switching unit 23 and the power supply voltage HV based on signals from the comparators 13a to 13c. The control circuit 5 has three input terminals and three output terminals. The three input terminals of the control circuit 5 are connected to the comparators 13a to 13c, respectively. One of the three output terminals of the control circuit 5 is connected to the switch means SW ₁ and SW ₂ . The other one of the three output terminals is connected to the control terminal of the high-voltage power supply 7. The other one of the three output terminals is connected to the output terminal 19.

The control circuit 5 obtains the amount of the detected light L based on the signals from the comparators 13a to 13c. When the detected light L is extremely weak (that is, when the light amount signal S ₁ is smaller than the reference voltage Vr ₁₂ ), the control signal S ₃ for switching the switch means SW ₁ and SW ₂ to the disconnected state is switched. The control signal S ₄ for setting the power supply voltage HV to a high voltage (for example, −1100 V) is sent to the high voltage power supply 7 while being sent to the means SW ₁ and SW ₂ . Further, when the intensity of the light to be detected L is slightly small (i.e., smaller when than and the reference voltage _{Vr 11} greater than the amount the signal _{S 1} is the reference voltage _{Vr 12),} the non-connected switch means SW ₁ and SW ₂ A control signal S ₃ for setting the state is sent to the switch means SW ₁ and SW ₂ , and a control signal S ₄ for making the power supply voltage HV low (eg, −400 V) is sent to the high voltage power source 7. Further, when the intensity of the detected light L is large (that is, when the light quantity signal S ₁ is larger than the reference voltage Vr ₁₁ or the light quantity signal S ₂ is larger than the reference voltage Vr ₂ ), the switch means SW ₁ and and sends a control signal _{S 3} to the SW ₂ and the connection state to the switch means SW ₁ and SW _2, and sends a control signal _{S 4} for a more low-pressure (e.g., -200 V) power supply voltage HV to the high voltage source 7. Further, the control circuit 5 provides a mode signal S ₅ indicating the control state of the switch means SW ₁ and SW ₂ and the high-voltage power supply 7 based on the incident light quantity to the outside of the photodetector 1 a via the output terminal 19.

The high-voltage power supply 7 has an output terminal for outputting a power supply voltage and a control terminal for controlling the power supply voltage. The output terminal of the high-voltage power source 7 is connected to the photocathode 33 and the voltage application means 21 via the resistance element R _1. A control terminal of the high voltage power source 7 is connected to the control circuit 5. High-voltage power supply 7 outputs the power supply voltage HV size indicated in the control signal S ₄ that is input from the control terminal from the output terminal.

The photodetector 1a and the light detection circuit 2a having the above-described configuration operate as follows. When the detection light L enters the photocathode 33 of the PMT 3, photoelectrons corresponding to the amount of incident light are generated at the photocathode 33. When the switch means SW ₁ and SW ₂ are unconnected, photoelectrons are multiplication secondary electrons by each dynode _Dy 1 _{~Dy n.} The multiplied secondary electrons are sent as output current I ₁ is collected to the anode 37 to the I / V converter 11b. Then, the I / V converter 11b, the output current _{I 1} is converted into intensity signal _{S 1.} Light intensity signals _{S 1,} along with being provided to the optical detector 1a outside via the output terminal 15b, it is fed to the comparator 13b, and 13c. When the incident light quantity to the photocathode 33 is smaller than the predetermined second light quantity, the above operation is continued. When the amount of light incident on the photocathode 33 is larger than the predetermined second light amount and smaller than the predetermined first light amount, the control circuit 5 causes the power supply voltage HV from the high voltage power source 7 to go to the low voltage side ( For example, it is switched from -1100V to -400V.

Further, when the amount of light incident on the photocathode 33 is greater than a predetermined first amount of light, the control circuit 5, the switch means SW ₁ and SW ₂ are switched from the disconnected state to the connected state, the high-voltage power supply 7 Is switched to a lower voltage side (for example, from -400 V to -200 V). When the switch means SW ₁ and SW ₂ are switched to the connected state, the photoelectrons generated at the photocathode 33 reach the dynode Dy ₁ , but are not emitted to the dynode Dy ₂ due to the reverse potential gradient. The electrons are not multiplied. The photoelectrons are output as an output current I ₂ from the dynode Dy ₁ . The output current I ₂ is sent to the I / V converter 11a. Then, the I / V converter 11a, the output current _{I 2} is converted to the light amount signal _{S 2.} Light quantity signal S ₂ together with is provided to the photodetector 1a outside via an output terminal 15a, it is sent to the comparator 13a. When the amount of light incident on the photocathode 33 is larger than the predetermined first light amount, the above operation is continued. Further, when the amount of light incident on the photocathode 33 is smaller than a predetermined first amount of light, the switch means SW ₁ and SW ₂ are switched from the connected state to the disconnected state by the control circuit 5, the power supply from the high-voltage power supply 7 The voltage HV is switched to the high voltage side (for example, from -200V to -400V).

According to the photodetector 1a and the light detection circuit 2a of the present embodiment described above, the same effects as the photodetector 1 and the light detection circuit 2 of the first embodiment can be obtained. Also, as in the present embodiment, the optical detector 1a and the light detection circuit 2a based on the output current I ₂ from the output current I _1, and dynodes Dy ₁ from the anode 37 of the first switching means 23 It is preferable to further comprise a control circuit 5 for controlling the switch means SW ₁ and SW ₂ . Thereby, the secondary electron multiplication factor (including the case where the secondary electron multiplication is not performed) in the PMT 3 can be automatically set according to the amount of light incident on the photocathode 33. In this case, it is more preferable that the value of the power supply voltage HV is automatically switched based on the output current I ₁ from the anode 37 and the output current I ₂ from the dynode Dy ₁ .

(Third embodiment)
Next, a third embodiment of the photodetector and the circuit for light detection according to the present invention will be described. FIG. 3 is a circuit diagram showing configurations of the photodetector 1b and the light detection circuit 2b according to the third embodiment. Referring to FIG. 3, the photodetector 1b includes a PMT 3 and a light detection circuit 2b. Among these, since the configuration of the PMT 3 is the same as that of the first embodiment, detailed description thereof is omitted.

Point light detecting circuit 2b of the present embodiment is different from the light detection circuit 2 of the first embodiment, when the amount of light incident on the photocathode 33 is very small, the m-th stage rather than the dynodes Dy ₁ ( in that taking out an output current from the dynodes Dy _m of 2 ≦ m ≦ n-1) .

The light detection circuit 2 b includes a voltage application unit 22 and a first switching unit 24. Voltage applying means 22 is a means for providing a predetermined potential gradient in the dynode _Dy 1 _{~Dy n} photocathode 33 and n stages. In the present embodiment, the voltage application unit 22 includes a first voltage application unit 22a and a second voltage application unit 22b. First voltage applying means 22a includes a Zener diode _D 1 to D _m and a resistor _{R 5} connected in series. The anode side of the Zener diode D ₁ is connected to the power supply terminal 17 via the resistance element R ₁ and is also connected to the photocathode 33. Cathode of the Zener diode D _m is connected to one end of the resistance element R _5. The other end of the resistance element R ₅ is connected to the reference potential line 43. Between the zener diode D _m and the resistance element R ₅ is dynode Dy _m via a resistor R ₄ is connected. A power supply voltage HV (<0) is supplied to the power supply terminal 17. With this configuration, photocathode 33 is supplied with the potential _{V k,} dynodes _Dy 1 _~Dy the _m Zener diode _D 1 to D _m and the potential _V 1 with a gradient by the resistance element _{R 5 ~V} m (> _{V k} ) Is given.

Second voltage applying means 22b has a resistance element _Rd m _{~Rd n.} Resistive element _Rd m ~ Rd _n are connected in series between the resistor element _{R 1} and the reference potential line 31. One end of the resistive element Rd _m is connected to the power supply terminal 17 via a resistor R _1. One end of the resistive element Rd _n is connected to the reference potential line 31. Between the resistive element _Rd m ~ Rd resistance elements adjacent to each other among the _n, are respectively connected to the dynodes _Dy m + 1 _{~Dy n.} Second voltage applying means 22b, by dividing the supply voltage HV by the resistor element _Rd m ~ Rd _n, generates a potential _{V m} + 1 ~V _n giving the dynode _Dy m + 1 _{~Dy n.} At this time, the second voltage application unit 22b generates the potentials V _{m + 1 to} V _n so that the potential of the subsequent dynode becomes higher. The second voltage applying unit 22b, the potential _{V m + 1} of the dynode _{Dy m + 1} is such that a potential higher than the potential _{V m} dynode Dy _m, generates each potential _{V m} + 1 ~V _n.

First switching means 24, of the dynode _Dy 1 ～Dy _n of n stages, with means for switching the reverse potential gradient is a predetermined potential gradient potential gradient between the dynode Dy _m and the dynode _{Dy m + 1} is there. In the present embodiment, the first switching means 24 has a switch means SW _3. One end of the switch means SW ₃ is connected to the dynode Dy _m through the resistance element R _4, the other end of the switch means SW ₃ is connected to the reference potential line 41. When the switch means SW ₃ are short-circuited, the potential _{V m} dynode Dy _m is higher reference potential than the potential _{V m + 1} of the dynode _{Dy m + 1,} the potential gradient between the dynode Dy _m and the dynode _{Dy m + 1} is reversed and Become. Note that, unlike the first embodiment, the magnitude of the power supply voltage HV supplied to the power supply terminal 17 is constant.

Further, the light detection circuit 2 b includes wirings 26 and 28. Wire 26 is means for extracting an output current _{I 3} from the dynode Dy _m. One end of the wiring 26 is connected between the dynode Dy _m and the resistance element R _4, the other end of the wiring 26 is connected to the output terminal 27c. The wiring 28 is a means for taking out the output current I ₁ from the anode 37. One end of the wiring 28 is connected to the anode 37, and the other end of the wiring 28 is connected to the output terminal 27a.

The photodetector 1b and the light detection circuit 2b having the above configuration operate as follows. When the detection light L enters the photocathode 33 of the PMT 3, photoelectrons corresponding to the amount of incident light are generated at the photocathode 33. If the amount of incident light is small, it sets the switch means SW ₃ of the first switching means 24 to the disconnected state. At this time, each of the photocathode 33 and the dynode _Dy 1 _{~Dy n,} the potential _V k of a predetermined potential gradient by the voltage application means _22, since V 1 ~V _n are given, generated in the photocathode 33 photoelectrons are multiplication secondary electrons are released in order to dynode Dy ₁ ~Dy _n. The multiplied secondary electrons are collected by the anode 37 and output from the anode 37 to become an output current I ₁ , which is provided to the output terminal 27 a via the wiring 28.

Further, when the incident light amount is large, it sets the switch means SW ₃ of the first switching unit 24 to the connected state. At this time, the potential gradient is reversed between the dynode Dy _m and the dynode _{Dy m + 1,} the potential _{V m} dynode Dy _m is higher than the dynode _{Dy m + 1} potential _{V m + 1.} After photoelectrons generated in the photocathode 33 is multiplication secondary electrons in the dynode _{Dy 1 ~Dy m-1,} the secondary electrons reach the dynode Dy _m. Photoelectrons reaching the dynode Dy _m is not released to the dynode Dy m _{+ 1} for the reverse potential gradient, no electrons are multiplied by the subsequent dynodes. Then, it is output as the output current _{I 3} from the dynode Dy _m, is provided to the output terminal 27c through the wiring 26.

In the optical detector and an optical detection circuit according to the present invention, it may be taken out first-stage dynode Dy ₁ and output current I ₃ from any dynode Dy _m between the last stage dynode Dy _n as in this embodiment . In this case, since the dynode _{Dy 1 ~Dy m-1} by a secondary electron multiplier output current _{I 3} is obtained, large relative to the amount of incident light, dynodes _Dy 1 ~ less m-1 stage than n stages A small electron multiplication factor can be realized by Dym _-1 . The output current I ₂ is extracted from the first stage dynode Dy ₁ as in the first embodiment (that is, corresponding to the case of m = 1 in the present embodiment), or the dynode Dy _m (2 ≦ m) subsequent to the first stage dynode Dy _1. Whether the output current I ₃ is taken out from ≦ n−1) may be determined based on the maximum amount of light incident on the photocathode 33.

Also, when taking out the output current _{I 3} from any dynode Dy _m between the first-stage dynode Dy ₁ and the final-stage dynode Dy _n as in this embodiment, conventional PMT extracting an output current _{I 1} from the anode 37 The power supply voltage HV in operation may be used as it is without switching. Since often takes some time to operation of switching the power supply voltage in the high voltage power supply, by not switching the supply voltage HV, the output current I ₁ from the operation mode and an anode 37 for taking out the output current I ₃ from the dynode Dy _m The switching time when switching between the operation modes to be taken out can be shortened.

(Fourth embodiment)
Next, a fourth embodiment of the photodetector and the circuit for light detection according to the present invention will be described. FIG. 4 is a circuit diagram showing configurations of the photodetector 1c and the photodetection circuit 2c according to the fourth embodiment. Referring to FIG. 4, the photodetector 1c includes a PMT 3 and a light detection circuit 2c. Among these, since the configuration of the PMT 3 is the same as that of the first embodiment, detailed description thereof is omitted.

  The difference between the light detection circuit 2c of the present embodiment and the light detection circuit 2 of the first embodiment is the presence or absence of the second switching means 45. The light detection circuit 2 c of this embodiment includes second switching means 45. The configuration of the photodetection circuit 2c other than the second switching unit 45 is the same as the configuration of the photodetection circuit 2 of the first embodiment.

Second switching means 45 is a means for switching the electric potential _V 3 ~V _n dynode _Dy 3 _{~Dy n,} so as to be substantially the same potential as the dynodes Dy _1. In this embodiment, the second switching means 45 is connected between the resistive element Rd ₂ and the resistor element Rd ₃ of the second voltage applying means 21b. Second switching means 45 includes a switch means SW _4. One end of the switch means SW ₄ is connected between the resistor element Rd ₂ and the resistor element Rd _3. The other end of the switch means SW ₄ is connected to the reference potential line 47. As the switch means SW _4, other mechanical switches, may be used an electrical switch such as a transistor.

The operation of the photodetector 1c and the light detection circuit 2c of this embodiment will be described. When the detection light L enters the photocathode 33 of the PMT 3, photoelectrons corresponding to the amount of incident light are generated at the photocathode 33. If the amount of incident light is small, it sets the switch means SW ₄ of switch means SW ₁ and the second switching means 45 of the first switching means 23 to the disconnected state. Note that the setting of the connection state / non-connection state of the switch means SW ₁ and SW ₄ may be performed manually or automatically based on the amount of incident light as in the second embodiment. Photoelectrons generated in the photocathode 33 is multiplication secondary electrons are released in order to dynode Dy ₁ ~Dy _n. The multiplied secondary electrons are collected by the anode 37 and output from the anode 37 to become an output current I ₁ , which is provided to the output terminal 27 a via the wiring 28.

Further, when the incident light amount is large, it sets the switch means SW ₄ of switch means SW ₁ and the second switching means 45 of the first switching means 23 to the connected state. At this time, the potential gradient between the dynode Dy ₁ and dynode Dy ₂ is reversed, the potential _V 3 ~V _n dynode _Dy 3 _{~Dy n} have the same potential (reference potential) to each other. Photoelectrons generated at the photocathode 33 are output from the dynode Dy ₁ to become an output current I _{2 and} are provided to the output terminal 27 _b via the wiring 25.

According to the photodetector 1c and the light detection circuit 2c of the present embodiment, the following effects can be obtained in addition to the effects of the photodetector 1 and the light detection circuit 2 of the first embodiment. That is, the light detection circuit 2c includes a second switching means 45 for switching the electric potential _V 3 ~V _n dynode _Dy 3 _{~Dy n,} so as to be substantially the same potential as the dynodes Dy _1. Thereby, the emission of secondary electrons from the dynode Dy ₁ is almost completely suppressed. Although it described taking the case where the dynodes Dy ₁ extracting an output current I ₂ as an example in the present embodiment, when taking out the output current from the dynodes Dy _m, it is preferable to connect the second switching means to the dynode Dy m _{+ 2.} In this case, second switch means, the potential _{V m} + 2 ~V _n dynodes _Dy m + 2 _{~Dy n,} switch to the dynode Dy _m substantially the same potential.

  The light detection circuit and the light detector according to the present invention described above can be used as, for example, a wide range light detector incorporated in an MTP reader or a luminometer. In recent years, optical filters having high OD (Optical Density: optical density) (for example, a fluorescent filter for cutting excitation light) have been demanded. When measuring the OD performance of such optical filters, conventional optical detection is required. The instrument has a narrow dynamic range, making it difficult to measure accurately. According to the light detection circuit and the light detector according to the present invention, an output current excellent in linearity can be obtained with a wide dynamic range of, for example, 11 digits or more, and therefore it becomes easy to measure the OD value of such an optical filter. . Conventionally, a method of attenuating high-intensity incident light using an ND filter (a neutral density filter) has been used to expand the dynamic range of the photodetector. According to the light detection circuit and the light detector according to the present invention, the dynamic range can be expanded without using an ND filter.

  Further, the light detection circuit and the light detector according to the present invention are not limited to the above-described embodiments, and various other modifications are possible. For example, in each of the above embodiments, the photocathode potential is a negative potential, but the photocathode potential may be a reference potential and the anode potential may be a positive potential. In this case, in order to reverse the potential gradient between predetermined dynodes, the first switching means may switch the dynode potential to an appropriate positive potential instead of the reference potential.

It is a circuit diagram which shows the structure of the photodetector by 1st Embodiment, and the circuit for light detection. It is a circuit diagram which shows the structure of the photodetector by 2nd Embodiment, and the circuit for light detection. It is a circuit diagram which shows the structure of the photodetector by 3rd Embodiment, and the circuit for light detection. It is a circuit diagram which shows the structure of the photodetector by 4th Embodiment, and the circuit for light detection.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,1a-1c ... Photo detector, 2, 2a-2c ... Photo detection circuit, 5 ... Control circuit, 7 ... High voltage power supply, 11a, 11b ... I / V converter, 13a-13c ... Comparator, 15a, 15b, 19, 27a to 27c ... output terminal, 17 ... power supply terminal, 21, 22 ... voltage applying means, 21a, 22a ... first voltage applying means, 21b, 22b ... second voltage applying means, 23, 24 ... First switching means, 33 ... photocathode, 35 ... multiplier, 37 ... anode, 39 ... vacuum tube, 45 ... second switching means.

Claims (5)

A photocathode that emits photoelectrons according to the amount of incident light, a dynode arranged in n stages (n is an integer of 2 or more), a multiplier that multiplies the photoelectrons, and an electron that has been multiplied by the multiplier A photodetection circuit connected to a photomultiplier tube having a collecting anode;
Voltage applying means for applying a predetermined potential gradient to the photocathode and the n-stage dynode;
The potential between the m-th dynode and the (m + 1) -th dynode when electrons are extracted from the m-th dynode (1 ≦ m ≦ n−1) of the n-th dynodes. And a first switching means for switching the gradient to a potential gradient opposite to the predetermined potential gradient.   2. The light detection according to claim 1, further comprising a control unit that controls the first switching unit based on a current amount from the anode and a current amount from the m-th stage dynode. Circuit.   The photodetection circuit according to claim 1, wherein the voltage applying unit includes a Zener diode that forms a potential gradient between the photocathode and the m-th dynode.   4. The device according to claim 1, further comprising a second switching unit configured to switch the potential of the dynodes after the m + 2 stage so as to be substantially the same potential as that of the m stage dynode. The circuit for light detection according to one item. A photocathode that emits photoelectrons according to the amount of incident light, a dynode arranged in n stages (n is an integer of 2 or more), a multiplier that multiplies the photoelectrons, and an electron that has been multiplied by the multiplier A photomultiplier tube having an anode to be
An optical detector comprising: the optical detection circuit according to claim 1.

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