JP4199517B2 - Optical measurement method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-sensitivity camera that multiplies and detects a weak light signal using an image intensifier.
[0002]
[Prior art]
FIG. 2 is a diagram showing a configuration of a conventional high-sensitivity camera, and FIG. 3 is a graph comparing pulse wave height distributions of one microchannel plate and two microchannel plates.
FIG. 1 shows a conventional high-sensitivity camera using an image intensifier 1 which is a light image intensifying type image conversion tube and a CCD element 2 with an optical fiber. The image intensifier 1 includes a photocathode 10. And one microchannel plate (MCP) 8 and a phosphor 9. When an optical signal is incident on the photocathode 10, photoelectrons proportional to the intensity of the optical signal are emitted from the photocathode 10, and the emitted photoelectrons enter the photoelectron incident surface of the MCP 8. The photoelectrons incident on the MCP 8 are amplified by the MCP 8, the multiplied electrons are emitted from the electron emission surface, the electrons emitted from the electron emission surface collide with the phosphor 9, and are converted into an optical signal again by the phosphor 9. The optical signal converted by the phosphor 9 is detected by a CCD element with an optical fiber.
[0003]
The image intensifier 1 is controlled by two high-voltage power supplies 3 and 4, and the high-voltage power supply 3 controls the voltage between the photoelectron incident surface of the MCP 8, the electron emission surface of the MCP 8 and the phosphor 9, The power source 4 controls the voltage between the photocathode 10 and the photoelectron entrance surface of the MCP 8. The high-voltage power supply 4 plays a role of a shutter. When the output of the high-voltage power supply 4 is set to −200 V, the potential difference between the photocathode 10 and the photoelectron incident surface of the MCP 8 becomes −200 V due to the resistor 5. The converted photoelectrons are sent to the MCP 8.
[0004]
The output of the high-voltage power supply 3 is normally about 6 KV, and when the output of the high-voltage power supply 3 is 6 KV, the potential difference between the photoelectron incident surface of the MCP 8 and the electron emission surface of the MCP 8 is 1 KV due to the resistors 6 and 7. Thus, the potential difference between the photoelectron incident surface of the MCP 8 and the phosphor 9 becomes 6 KV. When electrons enter the MCP 8, secondary electrons are generated on the inner wall of the MCP 8 by the voltage of 1 KV applied to the MCP 8, causing an electron multiplying action, and the incident photoelectrons are multiplied by about 10,000 times. The multiplied electrons are converted into an optical signal by the phosphor 9 and output as an optical signal. The optical signal is sent to the CCD element 2 with an optical fiber, and is read out as an output of 100 counts per photoelectron generated by the incidence of the optical signal. Further, when the output of the high voltage power supply 3 is lowered to 5 KV, the voltage inside the MCP 8 is reduced and the multiplication of electrons by the MCP 8 is suppressed. Therefore, the output of 10 counts per photoelectron generated by the incidence of the optical signal is obtained. Output from the CCD element 2 with fiber. By changing the output of the high-voltage power supply 3 in this way, the count value per photoelectron generated by the incidence of the optical signal is changed and used for gain adjustment.
[0005]
In addition, there is a high-sensitivity camera with two MCPs 8 in the image intensifier 1, and when two MCPs 8 are attached, the output of the high-voltage power supply 3 is higher than that in the case of one normal MCP 8. It is specified at about 7KV. When the output of the high voltage power supply 3 is 7 KV, a potential difference of 2 KV is applied between the photoelectron incident surface of the MCP 8 and the electron emission surface of the MCP 8, and a potential difference of 7 KV is applied between the photoelectron incident surface of the MCP 8 and the phosphor 9. In this state, the CCD element 2 with an optical fiber outputs an output of 10,000 counts per photoelectron generated by the incidence of an optical signal (see, for example, Patent Document 1).
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 05-187914 (FIGS. 8 and 9)
[0007]
[Problems to be solved by the invention]
However, the conventional high-sensitivity camera with one MCP 8 has a sufficiently high sensitivity because an output of 100 counts per photoelectron generated by the incidence of an optical signal is obtained, but the peak value distribution shown in FIG. As is clear from the comparison, the detection efficiency is lower than that of the high-sensitivity camera with one MCP 8 and the sensitivity is high, but there is a problem that the detection efficiency is not sufficient. FIG. 3 shows the variation of the peak value (electron multiplication amount: the number of emitted electrons) due to MCP8, and a graph showing the peak value distribution obtained for each predetermined amount of event (photoelectron incidence). (A) shows the peak value distribution when one MCP 8 is used, and (b) shows the peak value distribution when two MCPs 8 are used.
[0008]
In addition, in a high sensitivity camera with two conventional MCP8, if a specified voltage is applied, it becomes too high at 10,000 counts per photoelectron generated by the incidence of an optical signal, and a CCD with an optical fiber. Since the dynamic range of the element 2 is 65,000 counts, only a signal / noise ratio of about 6 can be obtained, and the dynamic range is lost.
[0009]
Furthermore, the high-sensitivity camera with one conventional MCP8 and the high-sensitivity camera with two conventional MCP8 are separate devices, and different devices are used according to the optical signal intensity to be detected. There is a problem that it is necessary to use properly, it takes extra time for replacement work, etc., and it is not easy to use.
[0010]
The present invention has been made in view of such problems, and the object of the present invention is to support a plurality of measurement methods by changing the setting according to the optical signal intensity to be detected, Further, the present invention is to provide an easy-to-use high-sensitivity camera that can also perform measurement with a high signal-to-noise ratio by accumulation type measurement with high detection efficiency.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention has the following configuration.
The gist of the invention described in claim 1 is that the photoelectron incident by the microchannel plate is multiplied to emit the electron, the multiplied electron is converted into an optical signal by the phosphor, and the converted optical signal is measured. A voltage applied to the microchannel plate and a potential difference between the electron emission surface of the microchannel plate and the phosphor are controlled independently of each other, and the voltage applied to the microchannel plate is set to an upper limit of multiplication. A first measurement method in which a potential difference between the electron emission surface of the microchannel plate and the phosphor is set to a first potential difference, and a voltage applied to the microchannel plate is less than a multiplication upper limit voltage. Set the potential difference between the electron emission surface of the microchannel plate and the phosphor A second measurement method for setting the first potential difference; a voltage applied to the microchannel plate is set to a multiplication upper limit voltage or more; and a potential difference between the electron emission surface of the microchannel plate and the phosphor is set to the first The optical measurement method is characterized in that it can be switched to a third measurement method for setting a second potential difference lower than the first potential difference.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
FIG. 1 is a diagram showing a configuration of an embodiment of a high sensitivity camera according to the present invention.
[0014]
The CCD detector, which is a high-sensitivity camera according to the present embodiment, is composed of an image intensifier 1 and a CCD element 2 with an optical fiber, and the image intensifier 1 includes a photocathode 10 and 2. A single microchannel plate (MCP) 8, a phosphor 9, a high voltage power source 4 that controls the voltage between the photocathode 10 and the photoelectron incidence surface of the MCP 8, a photoelectron incidence surface of the MCP 8, and an electron emission surface of the MCP 8. A high voltage power source 11 for controlling the voltage between the two MCPs 8, a high voltage power source 12 for controlling the voltage between the photoelectron incident surface of the MCP 8 and the phosphor 9, and outputs of the high voltage power sources 4, 11, 12. And a voltage setting unit 20 for setting.
[0015]
When an optical signal is incident on the photocathode 10, photoelectrons proportional to the intensity of the optical signal are emitted from the photocathode 10, and the emitted photoelectrons have a potential difference between the photocathode 10 and the photoelectron entrance surface of the MCP 8. Is incident on the photoelectron incident surface of the MCP 8. The photoelectrons incident on the MCP 8 are multiplied in accordance with the voltage applied to the MCP 8, the multiplied electrons are emitted from the electron emission surface, and the electrons emitted from the electron emission surface are the electron emission surface of the MCP 8 (photoelectron incidence Surface) and the phosphor 9 is incident on the phosphor 9 and converted again into an optical signal. The optical signal converted by the phosphor 9 is detected by the CCD element 2 with an optical fiber.
[0016]
The photomultiplier action inside the MCP 8 is such that the photoelectrons are multiplied more than a certain amount, and no further multiplication process occurs where the current density is increased by the multiplied electrons. That is, as the voltage applied to the MCP 8 is higher, the multiplication of electrons is promoted, but at a predetermined voltage or higher, the amount of multiplication of electrons (the number of electrons emitted from the electron emission surface) reaches a peak (hereinafter, The voltage at which the amount of electron multiplication reaches its peak is called the multiplication upper limit voltage). By applying a voltage equal to or higher than the multiplication upper limit voltage to the MCP 8, the amount of multiplication of electrons with respect to one incident photoelectron can be made uniform. Further, the potential difference between the electron emission surface of the MCP 8 and the phosphor 9 controls the amount of light generated per electron in the phosphor 9. Accordingly, the output brightness of the phosphor 9 is determined by the number of electrons incident on the phosphor 9 and the potential difference between the electron emission surface of the MCP 8 and the phosphor 9, and the voltage applied to the MCP 8 by the high voltage power source 11 is controlled. The number of electrons emitted from the electron emission surface (the number of electrons incident on the phosphor 9) is controlled, and the potential difference between the electron emission surface of the MCP 8 and the phosphor 9 is controlled by the high-voltage power supply 12, so The count value of the CCD element 2 with an optical fiber is controlled.
[0017]
As in the present embodiment, a high-sensitivity camera using two MCPs 8 is weak as the first measurement method, noise generated inside the image intensifier 1 and readout noise of the CCD element 2 with an optical fiber. It is usually used in photon counting image measurement methods that clearly separate a signal from a single photoelectron from a light phenomenon and detect only a signal component with high sensitivity. The voltage applied to the MCP 8 (the output of the high-voltage power supply 11) is set to about 2 KV that is equal to or higher than the multiplication upper limit voltage, and the voltage of the phosphor 9 is set to about 8 KV by the high-voltage power supply 11 and the electron emission surface of the MCP 8 and the phosphor 9 The potential difference between them is about 6 KV. In this case, the crest value distribution is that of the two MCPs shown in FIG. 3 (b), and the output of 10,000 to 1,000 counts per one photoelectron incident on the photoelectron incident surface of MCP8 is a CCD element with an optical fiber. 2 is used for measurement of extremely weak light emitted from the photocathode 10 by about 3 photoelectrons per second.
[0018]
The noise generated inside the image intensifier 1 and the readout noise of the CCD element 2 with an optical fiber rarely come out of noise caused by several thousand counts from the inside of the semiconductor. That is certain. Therefore, if the threshold value is set to 9,000, all of the above values can be counted as one optical signal. Reading out the CCD element 2 with an optical fiber takes about 0.3 seconds when reading at 1 MHZ in the case of 1024 × 256 elements, but reading it once every 3 seconds and counting 9,000 counts or more as one on the display screen 1 is displayed on the screen. Thereafter, the intensity information can be imaged by reading out every 3 seconds and strengthening the display where the light enters according to the count value.
[0019]
In addition, the high-sensitivity camera using two MCPs 8 of the present embodiment has a configuration in which the voltage applied to the MCP 8 and the phosphor 9 can be independently controlled by the high-voltage power supply 11 and the high-voltage power supply 12. Therefore, if the voltage applied to the MCP 8 is set to be less than the multiplication upper limit voltage, it can be used as a high-sensitivity camera using one MCP 8 as the second measurement method. When used as a high-sensitivity camera using a single MCP 8, the voltage applied to the MCP 8 (output of the high voltage power supply 11) is set to about 1.2 KV, which is less than the multiplication upper limit voltage, and the voltage of the phosphor 9 is set to a high voltage. The power supply 11 is set to about 7.2 KV, and the potential difference between the electron emission surface of the MCP 8 and the phosphor 9 is set to about 6 KV. In this case, the crest value distribution is that of the single MCP shown in FIG. 3A, which is incident on the photoelectron incident surface of the MCP 8 and an output of 100 counts or less is output from the CCD element 2 with an optical fiber for one photoelectron. Used for measuring relatively bright light.
[0020]
Furthermore, the high-sensitivity camera using two MCPs 8 according to the present embodiment has a configuration in which the voltage applied to the MCP 8 and the phosphor 9 can be independently controlled by the high-voltage power supply 11 and the high-voltage power supply 12. Therefore, the voltage applied to the MCP 8 is set to be equal to or higher than the multiplication upper limit voltage, and the potential difference between the electron emission surface of the MCP 8 and the phosphor 9 is set lower than usual. An accumulation-type measurement method with a high detection rate can be realized.
[0021]
The voltage applied to the MCP 8 (the output of the high-voltage power supply 11) is set to about 2 KV that is equal to or higher than the multiplication upper limit voltage, and the voltage of the phosphor 9 is set to about 7 KV by the high-voltage power supply 11 and the electron emission surface of the MCP 8 and the phosphor 9 The potential difference between them is about 5 KV. In this case, an output of 100 counts or less for one photoelectron incident on the photoelectron incident surface of the MCP 8 is output from the CCD element 2 with an optical fiber, and about 3 photoelectrons per second measured by the photon counting image measurement method is used for the photocathode. 10 is used to measure weak light that is slightly brighter than extremely weak light emitted from the light source 10.
[0022]
When the voltage applied to the MCP 8 is set to 2 KV, the peak value distribution of the two MCPs shown in FIG. 3B is obtained, and the detection efficiency is higher than that of the high-sensitivity camera using one MCP 8. Since the number of electrons is generated, the potential of the phosphor 9 is lowered so that the amount of light output from the output surface of the phosphor 9 is 100 counts per photoelectron incident on the photoelectron incident surface of the MCP 8. Therefore, it is possible to send an optical signal for 100 counts as one photoelectron to the CCD element 2 with an optical fiber. If the dynamic range of the CCD element 2 with an optical fiber is 65,000 counts, signal noise The ratio is 65,000 / 100, and approximately 650 photoelectrons can be measured at a time. The detection efficiency is the detection efficiency of the number of photoelectrons required for measurement, and means the ratio at which the photoelectrons incident on the photoelectron incident surface of the MCP 8 are measured by the CCD element 2 with an optical fiber.
[0023]
The voltage setting unit 20 sets the outputs of the high-voltage power supply 11 and the high-voltage power supply 12 in the first to third measurement methods described above by input from input means (not shown). Three modes for each measurement method can be set. In each mode, the output ranges of the high-voltage power supply 11 and the high-voltage power supply 12 that can be set are respectively determined, and measurement according to the respective purposes of the first to third measurement methods can be performed by selecting the mode. For example, in the mode corresponding to the first measurement method, the output of the high voltage power supply 11 is in the range of 1.8 to 2.0 KV which is not less than the multiplication upper limit voltage, and the output of the high voltage power supply 12 is in the range of 7.8 to 8 KV. In the mode corresponding to the second measurement method, the output of the high-voltage power supply 11 is in the range of 1 to 1.2 KV below the multiplication upper limit voltage, and the output of the high-voltage power supply 12 is in the range of 7 to 7.2 KV. In the mode corresponding to the third measurement method, the output of the high-voltage power supply 11 is in the range of 1.8 to 2.0 KV, which is less than the multiplication upper limit voltage, and the output of the high-voltage power supply 12 is the first and second measurements. In the method, each can be set in a range of 6.8 to 7 KV, which is lowered by the potential difference between the electron emission surface of the MCP 8 and the phosphor 9.
[0024]
If the CCD element 2 with an optical fiber has a gain adjusting function, the electron multiplication in the CCD element 2 with an optical fiber becomes possible, and the sensitivity on the CCD element side increases by 100 times. Then, it becomes possible to detect a portion of the optical signal that has been lost in the process of transferring the signal from the image intensifier 1 to the CCD device 2 with an optical fiber. In FIG. 2, the portion that cannot be detected is present on the left side of the graph regardless of whether it is a single MCP or a double MCP. However, since the signal of this portion can be picked up to some extent, the sensitivity is further improved. Also, since changing the image magnification is equivalent to changing the measurable threshold value, if the signal strength is insufficient when used in a way other than the photon counting image measurement method, gain is applied to this part. This further increases the detection efficiency.
[0025]
The pulse peak value distribution shown in FIG. 2 is normally determined by the number of MCPs 8, but if a special MCP 8 such as a curved MCP is used, for example, even one MCP 8 can switch between the two distributions depending on how the voltage is applied. . This case can also be handled as a two-sheet MCP of the present invention.
[0026]
When the number of MCPs is two or more, it is necessary to appropriately control the voltages of the high-voltage power supply 11 and the high-voltage power supply 12. Even in this case, the above three types of usage are possible.
[0027]
In the present embodiment, an interlace CCD element, a full frame CCD element, or the like is assumed as the CCD element 2 with an optical fiber, but a diode array or a focal plane array can be similarly applied.
[0028]
As described above, according to the present embodiment, the voltage applied to the two MCPs 8 by the high voltage power supply 11 and the high voltage power supply 12 and the potential difference between the electron emission surface of the MCP 8 and the phosphor 9 are independently determined. By configuring so as to be able to be set, there is an effect that it is possible to cope with a plurality of measurement methods by changing the setting according to the intensity of the optical signal to be detected.
[0029]
Furthermore, according to the present embodiment, the voltage applied to the MCP 8 is set to be equal to or higher than the multiplication upper limit voltage, and the potential difference between the electron emission surface of the MCP 8 and the phosphor 9 is set to be lower than usual. It is possible to perform measurement with an increased signal-to-noise ratio in the accumulation type measurement.
[0030]
Furthermore, according to the present embodiment, a mode is provided for each of a plurality of different measurement methods, and the output range of the high-voltage power supply 11 and the high-voltage power supply 12 that can be set for each mode is determined. A desired measurement method can be performed, and the convenience of use is improved.
[0031]
Note that the present invention is not limited to the above-described embodiments, and it is obvious that the embodiments can be appropriately changed within the scope of the technical idea of the present invention. In addition, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment, and can be set to a suitable number, position, shape, and the like in practicing the present invention. In each figure, the same numerals are given to the same component.
[0032]
【The invention's effect】
The high-sensitivity camera according to the present invention is configured such that the voltage applied to the two MCPs 8 and the potential difference between the electron emission surface of the MCP 8 and the phosphor 9 can be set independently by the high-voltage power supply 11 and the high-voltage power supply 12. Thus, there is an effect that it is possible to cope with a plurality of measurement methods by changing the setting according to the intensity of the optical signal to be detected.
[0033]
Furthermore, the high-sensitivity camera of the present invention sets the voltage applied to the MCP to be equal to or higher than the multiplication upper limit voltage, and sets the potential difference between the electron emission surface of the MCP and the phosphor to be lower than usual. There is an effect that it is possible to perform a measurement with an increased signal-to-noise ratio by an accumulation type measurement.
[0034]
Furthermore, the high-sensitivity camera of the present invention provides a mode for each of a plurality of different measurement methods, and determines an output range between a high-voltage power source and a high-voltage power source that can be set for each mode, so that only a desired mode can be selected. The measurement method can be performed, and there is an effect that usability is improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an embodiment of a high sensitivity camera according to the present invention.
FIG. 2 is a diagram illustrating a configuration of a conventional high-sensitivity camera.
FIG. 3 is a graph comparing pulse wave height distributions of one MCP and two MCPs.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image intensifier 2 CCD element with optical fiber 3, 4, 11, 12 High voltage power supply 5, 6, 7 Resistance 8 MCP
9 Phosphor 10 Photocathode 20 Voltage setting part

Claims (1)

An optical measurement method for multiplying photoelectrons incident by a microchannel plate to emit electrons, converting the multiplied electrons into an optical signal by a phosphor, and measuring the converted optical signal,
  Controlling independently the voltage applied to the microchannel plate and the potential difference between the electron emission surface of the microchannel plate and the phosphor,
  A first measurement method in which a voltage applied to the microchannel plate is set to a multiplication upper limit voltage or more, and a potential difference between the electron emission surface of the microchannel plate and the phosphor is set to a first potential difference;
  A second measurement method in which a voltage applied to the microchannel plate is set to be less than a multiplication upper limit voltage, and a potential difference between the electron emission surface of the microchannel plate and the phosphor is set to a first potential difference;
  A voltage applied to the microchannel plate is set to be equal to or higher than a multiplication upper limit voltage, and a potential difference between the electron emission surface of the microchannel plate and the phosphor is set to a second potential difference lower than the first potential difference. An optical measurement method characterized in that the measurement method can be switched.

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