JP2007184119A - Electron tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electron tube capable of improving light detection sensitivity while securing response speed. <P>SOLUTION: The electron tube 1 is provided with a housing 2 of which inside is maintained in vacuum, a photoelectric surface 10 formed on the vacuum side of an input surface plate 3 of the housing 2, a semiconductor element 11 which is installed so as to be opposed to the photoelectric surface 10 in the housing 2 and converts electrons emitted from the photoelectric surface 10 into an electric signal, and a plurality of electrodes which are provided at prescribed spacings between the photoelectric surface 10 and the semiconductor element 11 along the inner wall of the housing 2 electrically independently of the photoelectric surface 10 and have an opening part to pass the electrons. A positive voltage to the photoelectric surface 10 is impressed to an intermediate electrode 6a arranged at the nearest location to the photoelectric surface 10 out of the plurality of electrodes, and a voltage same as or lower than the voltage impressed on the intermediate electrode 6a is impressed to an intermediate electrode 6b arranged between the intermediate electrode 6a and the semiconductor element 11 out of the plurality of electrodes. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electron tube that is used as a photodetector for quantitatively measuring weak light, and in particular, detects an electron emitted from a photocathode by multiplying.

2. Description of the Related Art Conventionally, there has been known an electron tube that obtains a high gain by accelerating electrons emitted from a photocathode by the incidence of light and then entering the electron detection element such as a semiconductor element. This electron tube is described, for example, in Patent Document 1 below. In particular, the electron tube described in this document includes a plurality of ring-shaped intermediate electrodes fixed inside the bulb in order to introduce electrons generated from the photocathode into the electron incident surface of the semiconductor element.
Japanese Patent Laid-Open No. 10-31971

  In the electron tube described above, a voltage is applied to each of the plurality of intermediate electrodes to accelerate electrons from the photocathode toward the electron incident surface. On the other hand, in order to improve the light detection sensitivity at a constant response speed, it is required to increase the effective area of the photocathode while reducing the size of the detection element. However, in the conventional electron tube described above, when the effective area of the photocathode is expanded while maintaining the response speed, it becomes difficult to efficiently inject electrons into the electron incident surface of the detection element. The detection sensitivity tended to decrease.

  Therefore, the present invention has been made in view of such a problem, and an object thereof is to provide an electron tube capable of improving the light detection sensitivity while ensuring a response speed.

  In order to solve the above problems, an electron tube according to the present invention includes an envelope whose interior is maintained in a vacuum, a photocathode formed on the vacuum side of an incident window of the envelope, and a photocathode within the envelope. And an electron detection element that converts electrons emitted from the photocathode into an electric signal, and a predetermined distance between the photocathode and the electron detection element along the inner wall of the envelope. A plurality of electrodes that are electrically independent of the photocathode and have openings that allow electrons to pass therethrough, and are arranged at positions closest to the photocathode among the plurality of electrodes. The positive voltage is applied to the photocathode, and the second electrode disposed between the first electrode and the electron detection element among the plurality of electrodes is applied to the first electrode. A voltage equal to or lower than the voltage is applied.

  According to such an electron tube, electrons are emitted from the photocathode in response to the light incident on the incident window, and the electrons pass through the openings of the first and second electrodes and pass through the first electrode and the second electrode. The electric field formed by the second electrode is accelerated toward the electron detection element and focused toward the electron detection element. Thereafter, the electrons incident on the electron detection element are converted into electrical signals and output. Here, since a positive voltage with respect to the photocathode is applied to the first electrode, electrons can be sufficiently accelerated, and a voltage equal to or lower than the voltage of the first electrode is applied to the second electrode. Since the voltage is applied, the electrons can be efficiently focused on the electron detection element in a narrow area. Therefore, the detection sensitivity for incident light can be sufficiently improved even when the area of the photocathode is increased and the size of the electron detection element is reduced in order to ensure the required response speed. it can. As a result, it is possible to satisfy the demands of ensuring a wide effective area as a light input surface and having a high light detection sensitivity, in particular, capable of detecting single photons.

  It is preferable that a voltage equal to or lower than the voltage on the photocathode is applied to the second electrode. By providing such a second electrode, electrons can be more effectively focused from the photocathode toward the electron detection element.

  The plurality of electrodes may further include a third electrode provided between the second electrode and the electron detection element and having a tip portion that forms an opening that extends toward the photocathode and allows electrons to pass therethrough. preferable. In this case, it is possible to minimize the penetration of the electric field to the electron detection element side, suppress the generation of ion feedback, and improve the electron focusing effect.

  Furthermore, it is preferable that the plurality of electrodes further include a fourth electrode that is provided between the second electrode and the electron detection element and to which a voltage equal to or higher than a voltage applied to the first electrode is applied. With such a configuration, it is possible to further increase the focusing effect and the acceleration effect on the electrons incident on the electron detection element.

  It is also preferable to further include a cathode provided in electrical communication with the photocathode between the photocathode and the first electrode. When such a cathode is provided, the electron convergence effect on the front surface of the photocathode (the space between the photocathode and the first electrode) can be further improved.

  According to the electron tube of the present invention, it is possible to improve the light detection sensitivity while ensuring the response speed.

  Hereinafter, preferred embodiments of an electron tube according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a longitudinal sectional view of an electron tube 1 which is an embodiment of the electron tube of the present invention. The electron tube 1 accelerates the electrons emitted from the photocathode in response to the incidence of light, and obtains a high gain in the semiconductor element, thereby enabling detection of weak light. Hybrid Photo-Detector).

  As shown in the figure, the electron tube 1 has an envelope 2 whose inside is kept in a vacuum, and this envelope 2 includes a glass disk-shaped input face plate (incident window) 3, a cylinder Between the first side plate 5a and the second side plate 5b formed by dividing the side plate 5 into four parts, and a cylindrical side plate 5 made of an insulating material such as ceramic. A ring-shaped intermediate electrode (first electrode) 6a fixed in such a way as to be fixed, and a ring-shaped intermediate electrode (second electrode) 6b fixed so as to be sandwiched between the second side plate 5b and the third side plate 5c, , A ring-shaped intermediate electrode (fourth electrode) 6c fixed so as to be sandwiched between the third side plate 5c and the fourth side plate 5d, a metal flange 7, and a disc hermetically connected to the metal flange 7. These members 3, 4, 5, 6, 7, and 8 are stacked concentrically with each other. It has been.

  Here, the side plate 5 having the intermediate electrode 6 is provided between the cathode electrode 4 and the metal flange 7, and one end of the side plate 5 is airtightly joined to the end surface of the cathode electrode 4 by brazing or the like. The other end of the side plate 5 is airtightly joined to a metal flange 7 provided on the outer periphery of the stem 8 by brazing or the like. Further, these intermediate electrodes 6a, 6b, 6c form a ring shape having an opening centered on the central axis Z of the envelope 2, and will be described later with a predetermined interval along the inner wall of the side plate 5. The photocathode 10 is disposed electrically independently. Here, the outer diameters of the cylindrical portions of the cathode electrode 4, the side plate 5, and the metal flange 7 are substantially the same, and the inner diameter of the cathode electrode 4 is smaller than the inner diameter of the side plate 5. Therefore, the inner wall surface of the cathode electrode 4 is located inside the inner wall surface of the side plate 5 from one end to the other end of the cathode electrode 4 along the central axis Z. On the other hand, the inner diameters of the openings of the intermediate electrodes 6a, 6b, 6c are made as small as possible within the range where they do not interfere with the electron trajectory, that is, within the range where they are not extremely small compared with the diameter of the photocathode 10 described later. The electrodes 6 a, 6 b, 6 c protrude further inward than the cathode electrode 4 from the inner wall surface of the cylindrical side plate 5. Thereby, the charging of the side plate 5 by stray electrons when controlling the trajectory of the electrons emitted from the photocathode 10 and the influence on the electron trajectory due to this can be eliminated. The intermediate electrodes 6a, 6b, 6c are integrated with the side plate 5 by being fixed by brazing or the like while being sandwiched between the side plates 5.

  Further, a ring-shaped rising electrode (third electrode) 9 is fixed to the central axis Z side of the metal flange 7 of the envelope 2. The rising electrode 9 is arranged concentrically with the metal flange 7 and has an opening having a smaller diameter than the intermediate electrodes 6 a, 6 b, 6 c, and the opening is formed on the inner wall of the side plate 5 toward the input face plate 3. A substantially columnar tip portion 9a extending along the axis is formed.

  The input face plate 3 has a photocathode 10 on the inner surface on the vacuum side. The input face plate 3 is integrated with the cathode electrode 4 through a low melting point metal (for example, indium) after the photocathode 10 made of GaAsP or the like is formed.

  On the vacuum side surface of the stem 8, a semiconductor element (electron detection element) 11 including an APD (avalanche photo diode) is fixed so as to face the photocathode 10. An APD is a semiconductor element that joins a high-concentration P region and an N region and forms an electric field high enough for avalanche amplification there. The semiconductor element 11 is provided so as to penetrate through the stem 8 when the electrons emitted from the photocathode 10 irradiate the electron incident surface, which is the surface, to multiply the electrons and convert them into an electrical signal. Output to the outside via the pin 12.

  Next, an example of the configuration of the drive circuit connected to the electron tube 1 will be described with reference to FIG. As shown in the figure, the electron tube 1 is housed in a housing 20, and the photocathode 10, the intermediate electrodes 6 a, 6 b, 6 c and the rising electrode 9 are connected to a DC power source 21 outside the housing 20. . Here, the voltage divided by the resistance elements 22, 23, and 24 is applied to the photocathode 10, the intermediate electrodes 6a, 6b, and 6c, and the rising electrode 9 so that each voltage has a predetermined voltage value. Has been. Here, the cathode electrode 4 is electrically connected to the photocathode 10, and the same voltage as that of the photocathode 10 is applied to the cathode electrode 4. In addition, a bias voltage is applied to the semiconductor element 11 by a bias power supply 25 connected to the cathode outside the housing 20, and an electric signal for light detection is externally transmitted via a coaxial cable 26 connected to the anode. Is output.

  By such a drive circuit, the resistance elements 22, 23, and 24 are selected so that a positive voltage is applied to the photocathode 10 to the intermediate electrode 6a that is closest to the photocathode 10. The same voltage as that applied to the photocathode 10 is applied to the intermediate electrode 6b in the subsequent stage of the electrode 6a. Here, the same voltage as that of the photocathode 10 is applied to the intermediate electrode 6b, but a voltage equal to or lower than the voltage of the intermediate electrode 6a may be applied to the intermediate electrode 6b by adding a resistance element. In order to efficiently converge the electrons, it is preferable to apply a voltage equal to or lower than the intermediate value between the voltage on the photocathode 10 and the voltage on the intermediate electrode 6a to the intermediate electrode 6b. It is more preferable to apply a voltage equal to the voltage of the photocathode 10 in terms of simplification of the configuration. On the other hand, a voltage higher than the voltage of the intermediate electrode 6a is applied to the intermediate electrode 6c in order to make the convergence and acceleration of the electrons emitted from the photocathode 10 more efficient.

  3 to 6 show the simulation results of the electron trajectory and potential distribution in the cross section along the central axis Z inside the electron tube 1 when the voltage applied to the intermediate electrode 6b is changed. In this case, the electron tube 1 has a photocathode 10 having a diameter of 18 mm formed on the vacuum side surface of the input face plate 3 having a diameter of about 23.9 mm, and a semiconductor element 11 having a diameter of an electron incident surface of about 3 mm. The electrode 6a is 7 mm from the input face plate 3, the intermediate electrodes 6a, 6b, 6c are arranged at a distance of 3.5 mm, and the distance between the metal flange 7 and the intermediate electrode 6c is 6.5 mm. In addition, as voltages applied by the drive circuit, voltages applied to the photocathode 10, the intermediate electrode 6a, the intermediate electrode 6c, and the rising electrode 9 are -8.5 kV, -7.5 kV, -5.0 kV, and 0 V, respectively. The bias voltage to the semiconductor element 11 was set to -100V.

  FIG. 3 shows an equipotential line E1 and an electron trajectory P1 when a voltage -9.0 kV lower than that of the photocathode 10 is applied to the intermediate electrode 6b. Thereby, an electric field for accelerating electrons from the photocathode 10 toward the semiconductor element 11 is formed by the effects of the intermediate electrodes 6a, 6b, 6c and the rising electrode 9, and in particular, the openings of the intermediate electrode 6a and the rising electrode 9 are formed. It can be seen that an electric field for converging electrons in the central axis Z direction is formed between the vicinity. Further, FIGS. 4, 5 and 6 respectively show equipotential lines E2, E3, E4 when the voltage is increased stepwise to the intermediate electrode 6b as -8.5 kV, -8.0 kV, -7.5 kV, respectively. Electron trajectories P2, P3, and P4 are shown. From these results, by applying a voltage equal to or lower than the voltage of the intermediate electrode 6a to the intermediate electrode 6b, an acceleration electric field and a convergence electric field are efficiently formed from the photocathode 10 to the semiconductor element 11, and particularly as shown in FIG. It can be seen that the convergence efficiency on the surface of the semiconductor element 11 is highest when the same voltage as that of the photocathode 10 is applied to the intermediate electrode 6b.

  The operational effects of the electron tube 1 described above will be described. Electrons are emitted from the photocathode 10 in response to the light incident on the input faceplate 3, and these electrons pass through the openings of the intermediate electrodes 6 a, 6 b, 6 c, and the semiconductor is generated by the electric field formed by these intermediate electrodes. It is accelerated toward the element 11 and focused toward the center of the electron incident surface of the semiconductor element 11. Thereafter, the electrons incident on the surface of the semiconductor element 11 are converted into electrical signals for light detection and output.

  Here, since a positive voltage is applied to the intermediate electrode 6a with respect to the photocathode 10, and a voltage higher than that of the intermediate electrode 6a is applied to the intermediate electrode 6c, electrons are sufficiently supplied in the direction along the central axis Z. While being able to accelerate, since the voltage below the voltage of the intermediate electrode 6a is applied to the intermediate electrode 6b, an electron can be efficiently focused on the semiconductor element 11 in a narrow area. Furthermore, when a voltage equal to or lower than the voltage of the photocathode 10 is applied to the intermediate electrode 6 b, electrons can be more effectively focused from the photocathode 10 toward the semiconductor element 11. Further, by providing the rising electrode 9 between the intermediate electrode 6c and the semiconductor element 11, the penetration of the electric field to the semiconductor element 11 side is minimized, and the occurrence of ion feedback is suppressed, thereby degrading the detection sensitivity. In addition to preventing, the electron focusing effect can be further improved.

  Therefore, the presence of the intermediate electrode 6 and the rising electrode 9 makes it possible to increase the area of the photocathode in order to improve the photodetection sensitivity, and to reduce the size of the semiconductor element in order to ensure the required response speed. Even in this case, the detection sensitivity for incident light can be sufficiently improved. As a result, it is possible to satisfy the demands of ensuring a wide effective area as a light input surface and having a high light detection sensitivity, in particular, capable of detecting single photons.

  In addition, this invention is not limited to embodiment mentioned above. For example, the rising electrode 9 provided inside the metal flange 7 of the electron tube 1 may be omitted. FIG. 7 is a longitudinal sectional view showing a modification of the electron tube in such a case. FIG. 8 shows the simulation result of the electron trajectory and potential distribution in the cross section along the central axis Z in the electron tube 101 of FIG. Here, the applied voltage to the photocathode 10, the intermediate electrode 6a and the intermediate electrode 6c and the bias voltage to the semiconductor element 11 are set in the same manner as in FIGS. 3 to 6, and the applied voltage to the intermediate electrode 6b is photoelectrically set. The same voltage as that of the surface 10 was set. Also in such an electron tube 101, the presence of the intermediate electrodes 6a, 6b, 6c can sufficiently accelerate electrons in the direction along the central axis Z, and the intermediate electrode 6b has a voltage equal to or lower than the voltage of the intermediate electrode 6a. Since a voltage is applied, electrons can be efficiently focused on the semiconductor element 11 in a narrow area.

  Further, as the semiconductor element 11, other electron detection elements such as a CCD may be used instead of the APD.

It is a longitudinal cross-sectional view of the electron tube which is one Embodiment of the electron tube of this invention. It is a circuit diagram which shows an example of the drive circuit connected to the electron tube of FIG. It is a figure which shows the simulation result of the electron orbit and electric potential distribution in the cross section along the center axis line inside the electron tube of FIG. It is a figure which shows the simulation result of the electron orbit and electric potential distribution in the cross section along the center axis line inside the electron tube of FIG. It is a figure which shows the simulation result of the electron orbit and electric potential distribution in the cross section along the center axis line inside the electron tube of FIG. It is a figure which shows the simulation result of the electron orbit and electric potential distribution in the cross section along the center axis line inside the electron tube of FIG. It is a longitudinal cross-sectional view of the electron tube which is a modification of this invention. It is a figure which shows the simulation result of the electron orbit and electric potential distribution in the cross section along the center axis line inside the electron tube of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,101 ... Electron tube, 2 ... Envelope, 3 ... Input face plate (incident window), 4 ... Cathode electrode (cathode), 5 ... Side plate, 6 ... Intermediate electrode, 6a ... Intermediate electrode (1st electrode), 6b ... Intermediate electrode (second electrode), 6c ... Intermediate electrode (fourth electrode), 9 ... Rising electrode (third electrode), 9a ... Tip, 10 ... Photocathode, 11 ... Semiconductor element (electron detection element) ).

Claims (5)

An envelope whose interior is maintained in a vacuum;
A photocathode formed on the vacuum side of the entrance window of the envelope;
An electron detection element that is provided so as to face the photocathode inside the envelope and that converts electrons emitted from the photocathode into an electric signal;
A predetermined distance is provided between the photocathode and the electron detection element along the inner wall of the envelope, and is provided electrically independently from the photocathode and has an opening through which electrons pass. A plurality of electrodes,
A positive voltage with respect to the photocathode is applied to the first electrode disposed at a position closest to the photocathode among the plurality of electrodes,
A voltage equal to or lower than the voltage applied to the first electrode is applied to the second electrode disposed between the first electrode and the electron detection element among the plurality of electrodes.
An electron tube characterized by that. A voltage equal to or lower than the voltage of the photocathode is applied to the second electrode.
The electron tube according to claim 1, wherein: The plurality of electrodes further includes a third electrode provided between the second electrode and the electron detection element, and having a tip portion that extends toward the photocathode and forms an opening through which electrons pass. ,
The electron tube according to claim 1 or 2, wherein The plurality of electrodes further includes a fourth electrode provided between the second electrode and the electron detection element, to which a voltage equal to or higher than a voltage applied to the first electrode is applied.
The electron tube according to any one of claims 1 to 3, wherein: A cathode provided in electrical communication with the photocathode between the photocathode and the first electrode;
The electron tube according to any one of claims 1 to 4, wherein:

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