JPH0479466B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a streak tube and a streak device using the streak tube that can measure temporal brightness changes of light that change at high speed on the order of picoseconds. Regarding.

(Prior Art) A streak device is a device that converts a temporal intensity distribution of light to be measured into a spatial intensity distribution on an output surface.

It is used for analysis of ultra-high-speed photodevelopment because it can provide time resolution on the order of picoseconds.

First, the configuration and operation of a conventional streak device will be briefly described.

FIG. 7 is a sectional view showing the structure of a conventional streak tube, including the tube axis, taken along a plane parallel to the deflection electrode, and a schematic diagram showing the relationship between the photocathode and the optical image.

FIG. 8 is a sectional view taken along a plane including the tube axis of the stream tube and perpendicular to the deflection electrode. One end surface of the vacuum-tight container 103 of the streak tube forms an entrance window 101 where an optical image to be analyzed is formed, and the other end surface forms an exit window 102 from which a processed optical image is output.

Along the tube axis of this vacuum-tight container 103, photocathode 10 is successively placed between the entrance window 101 and the exit window 102.
4, mesh electrode 105, focusing electrode 106, aperture electrode 107, deflection electrode 108, fluorescent surface 10
9 are arranged.

and a focusing electrode 106 for the photocathode 104;
A higher voltage is applied to the mesh electrode 105 and the aperture electrode 107 in this order, and then the fluorescent surface 10
9 is given the same potential as the aperture electrode 107.

Assume that an optical image 104a is projected onto the photocathode 104 through the entrance window 101 on a line passing through the center of the photocathode 104 using a device (not shown).

The photocathode 104 emits an electron image corresponding to the optical image, which is accelerated by the emitted electron mesh electrode 105, focused by the focusing electrode 106, passes through the aperture electrode 107, and is made incident on the gap between the deflection electrodes 108. Ruru.

While this linear electron image passes through the gap between the deflection electrodes 108, a gradient deflection voltage is applied to the deflection electrodes 108.

The direction of the electric field generated by this voltage is perpendicular to the tube axis and the linear electron image (perpendicular to the plane of the paper in the cross-sectional view of Fig. 7, parallel to the plane of the paper in Fig. 8), and its strength depends on the deflection voltage. Proportional.

The light is then deflected by the deflection electric field of the deflection electrode 108 and made incident on the fluorescent surface 109.

The direction of deflection is indicated by arrow 120 in FIG. A linear electron beam is scanned on the fluorescent surface 109 perpendicular to the linear direction, so that a linear optical image projected onto the photocathode 104 is finally displayed on the fluorescent surface 109. Optical images arranged sequentially in time perpendicular to the direction of the line, a so-called streak image, are formed.

Therefore, a change in brightness in the arrangement direction of the streak image, that is, in the sweep direction, represents a temporal change in the intensity of the optical image incident on the photocathode 104.

(Problems to be Solved by the Invention) In the conventional streak tube described above, since the photoelectrons emitted from the photocathode have various energies, a group of photoelectrons emitted from the photocathode at the same time is fluorescent, which is a swept surface. The times at which they reach the surface are scattered and have a temporal spread.

This temporal spread is a major factor in impairing the time resolution of streak tubes.

In order to reduce this temporal spread, the electrons emitted from the photocathode are uniformly and rapidly accelerated.

Generally, in a streak tube, as shown in FIGS. 7 and 8, a mesh electrode 105 is provided close to the photocathode 104, and photoelectrons are rapidly accelerated.
This suppresses the travel time spread that occurs when photoelectrons travel at low speeds.

Generally, the travel time spread Δt that occurs around this area is
It is shown by the following formula.

Δt≒2.34×10 ^-6 ×(Δε) ^1/2 /E(S) Here, E is the electric field between the photocathode and the mesh (V/
m), Δε is the half-width [eV] of the energy distribution of photoelectrons emitted from the photocathode.

For example, if 1000V is applied between the photocathode and the mesh, and the distance between them is 1 mm, E will be 1×10 ⁶ (V/m).

On the other hand, Δε is generally determined by the wavelength of the light to be measured and the type of photocathode used; for example, if the wavelength is 0.53 μm
If the photocathode is a multi-alkali photocathode, then Δε
is approximately 0.5eV.

Substituting these values into the above equation shows that the travel time spread of photoelectrons near the photocathode at this time is approximately 1.7 ps.

In order to further reduce the travel time spread, the electric field between the photocathode and the mesh can be increased.

Furthermore, the inventors of the present invention have also focused on the fact that the sensitivity of the photocathode in the long wavelength region can be increased by increasing the electric field, which is known in the past.

FIG. 9 is a graph showing the relationship between the electric field between the photocathode and the mesh electrode and the wavelength sensitivity of the photocathode.

This graph uses S-20 (standard of the American Electronics Industries Association) as a photocathode, and wavelengths of 0.6 μm, 0.8 μm,
This is a measurement of the electric field dependence of incident light of 0.85 μm. This graph shows that as the electric field increases,
This shows that the sensitivity increases, especially the sensitivity on the long wavelength side.

As is well known, in order to increase the electric field on the surface of the photocathode, it is sufficient to narrow the distance between the photocathode and the mesh and increase the voltage applied therebetween.

However, in conventional streak tubes, there is a problem in that dark current increases when the electric field between the photocathode and the mesh electrode is increased.

FIG. 10 is a graph showing the relationship between accelerating electric field and dark current in a conventional streak tube.

As shown in FIG. 10, when the accelerating electric field is increased, the dark current gradually increases so that it is emitted from the photocathode.

The generation of such dark current reduces the S/N of the streak image.

Furthermore, if there are minute scratches on the surface of the photocathode, electrons are emitted by field emission. The inventors of the present invention refer to the noise image that appears on the output surface due to these electrons as white flaws (or white spots).

In addition, in order to improve the S/N of the streak image obtained with a streak tube, photoelectrons are emitted from the photocathode for a short period of time when the output surface is swept, and at other times, the voltage of the mesh electrode is lowered. A method can be considered to prevent photoelectrons from being generated from the surface.

In order to increase the electric field between the photocathode and the mesh electrode, it is sufficient to increase the amplitude of the applied pulse voltage during operation in the forward direction (acceleration direction), but generation of short duration voltage pulses with large amplitudes is difficult. It's not easy.

As mentioned above, by narrowing the distance between the photocathode and the mesh electrode, which is the accelerating electrode, a large accelerating voltage can be obtained with a low voltage.

However, there is a problem in that it is difficult to achieve mechanical precision when narrowing the spacing to, for example, 1 mm or less.

Furthermore, when a method of manufacturing a photocathode is adopted in which photocathode material is supplied to an entrance window through a mesh electrode, there is a problem in that the photocathode is not formed in a portion that is in the shadow of the mesh electrode.

For these reasons, in the streak tube, the distance between the photocathode and the mesh electrode cannot be made extremely narrow.

The main object of the present invention is to provide a streak tube and a streak device using the streak tube that can solve the above-mentioned problems.

(Means for Solving the Problem) In order to achieve the above object, the streak tube according to the present invention includes a streak tube having a photocathode formed on the inner surface of an entrance window and an electrode for accelerating and deflecting photoelectrons generated by the photocathode. In the tube, a protrusion is formed on a part of the inner surface of the entrance window, a photocathode is formed on the surface of the protruding end of the protrusion through an electrode thin film connected to an external circuit, and the photocathode is connected to the input window. It is disposed closest to the accelerating electrode disposed facing the inner surface of the window, and is configured to accelerate photoelectrons with the accelerating electrode and deflect them with the deflecting electrode.

The streak device according to the present invention also includes: an airtight container having an entrance window; a protrusion formed on a part of the inner surface of the entrance window; and an electrode thin film connected to an external circuit on the surface of the protruding end of the protrusion. a photocathode formed through the photocathode; an accelerating electrode for rapidly accelerating the photoelectron beam emitted from the photocathode in the direction of the output screen; and an acceleration electrode for refocusing the photoelectron image emitted from the photocathode onto the output screen. an anode electrode having a focusing electrode and an aperture for forming an image; a deflection electrode for sweeping the photoelectron beam on an output screen; a phosphor screen for forming an output image; and an output having the phosphor screen on its inner surface. A streak tube consisting of a window, and means for applying a pulse-like accelerating voltage to the accelerating electrode in the accelerating direction so that photoelectrons reach the screen only when the photoelectron beam is swept.

(Example) The present invention will be described in more detail below with reference to the drawings and the like.

1 and 2 are views showing a first embodiment of the streak tube according to the present invention, in which FIG. 1 is a cross-sectional view taken along a plane parallel to the deflection electrode;
FIG. 2 is a cross-sectional view of the streak tube taken along a plane that includes the tube axis and is perpendicular to the deflection electrode.
FIG. 3 is an enlarged sectional view showing the relationship between the central part of the entrance window and the accelerating electrode in the first embodiment.
This embodiment does not differ from the structure of the streak tube described above with reference to FIGS. 7 and 8, except for the relative positional relationship between the entrance window and the accelerating electrode.

A glass fiber 131 having a diameter of 40 μm is fixed at the center of the entrance window 101 so as to extend to the surface of the entrance window.

This glass fiber 131 can be made by making a small hole in the entrance window, inserting the glass fiber 131, and fixing it by heating, or by dividing the entrance window and providing corresponding grooves and sandwiching the glass fiber 131 therein. Alternatively, it may be fixed by heating.

The glass fiber 131 extends 200 μm from the inner surface of the entrance window toward the mesh electrode, which is an accelerating electrode, and the radius of curvature of the surface is 20 μm.

An electrode thin film 132 connected to an external circuit is formed on the side surface of the protruding end of the glass fiber 131 and on the inner surface of the entrance window.

A photocathode 134 is formed on the surface of the glass finder 131 via the electrode thin film 132 attached to the side surface of the glass fiber 131.

The distance between the photocathode 134 and the mesh electrode 105 is about 2 mm.

It is sufficient that the photocathode 134 is formed on the protruding end, but there is no problem in operation even if the photocathode 134 is attached to the inner surface of the entrance window.

The field enhancement effect resulting from structures protruding from the substrate has been well known for some time.

FIG. 4 is a schematic diagram for explaining the electric field enhancement effect.

In general, V between parallel plates separated by a distance d [m]
When a voltage of [V] is applied, the average electric field E formed during this time is given by E=V/d [V/m].
At this time, as shown in FIG. 4, suppose that there is a protrusion on one of the plates whose height h can be considered sufficiently small compared to the distance d.

If the top of the protrusion is a hemisphere with radius r, and the portion of the pillar below it is, for example, cylindrical, the electric field on the surface near the top with radius r will be enhanced by a factor of βE.

β is expressed by the following formula.

β=h/r+2 ………(1) For example, if r is 10 μm and height h is 100 μm, then β
If the value is 10, the electric field will be strengthened approximately 10 times.

In general, equation (1) does not apply when the protrusion does not satisfy h<<d or is not cylindrical in shape, but electric field enhancement occurs, and the greater the height of the protrusion, the sharper it becomes. It will be strengthened as much as possible.

The present invention takes advantage of this phenomenon, and in order to perform time resolution in a streak tube, incident light is incident on the photocathode in a dotted or linear manner, and only this portion is used as a photocathode. The shape of the part into which the light to be measured is incident is made to protrude in the form of a point or a line, this part forms a photocathode, and a voltage is applied between it and the accelerating electrode.

This makes it possible to create a stronger electric field near the surface of this area compared to other areas, which is advantageous in terms of time resolution and red sensitivity of the photocathode.

On the other hand, since this strong electric field is limited to only the area where point-like or linear light is incident, the probability of background rise due to increase in dark current and the occurrence of white spots is lower than that of conventional ones. It decreases by that area ratio.

On the other hand, due to the electric field enhancement effect, the voltage applied between the photocathode substrate and the mesh electrode is 1/1/1 compared to that generated by a simple parallel plate with the same strength as the electric field formed on the surface of the protrusion. β is sufficient, and the gate operation becomes easy.

The tip surface (photocathode 1) of the embodiment shown in FIG.
When formula (1) is applied, the electric field on the surface of 34 becomes 12 times the electric field on the surface of the electrode thin film on the inner surface of the entrance window.

Between the electrode thin film 132 and mesh electrode 105
When a voltage of 500V is applied, the electric field at the photocathode 134 becomes 3KV/mm.

Next, the operation of the streak tube will be explained.

The light to be measured is introduced into the incident window 10 by a device (not shown).
The light is incident on a location corresponding to the protrusion where the photocathode 1 is formed.

A portion of the surface of the entrance window 101 other than the portion corresponding to the photocathode may be shielded.

The light to be measured is guided to the photocathode 134 by the glass fiber 131 and causes photoelectrons to be emitted.

As mentioned above, the electric field near the photocathode 134 is extremely large, so the emitted electrons are absorbed by the mesh electrode 1.
05, is focused by the focusing electrode 106, passes through the aperture electrode 107, and is made incident on the gap between the deflection electrodes 108.

While this linear electron image passes through the gap between the deflection electrodes 108, a gradient deflection voltage is applied to the deflection electrodes 108.

The direction of the electric field generated by this voltage is perpendicular to the tube axis and the linear electron image (perpendicular to the plane of the paper in the cross-sectional view of Fig. 1, parallel to the plane of the paper in Fig. 2), and its strength depends on the deflection voltage. Proportional.

The light is then deflected by the deflection electric field of the deflection electrode 108 and made incident on the fluorescent surface 109.

The direction of deflection is indicated by arrow 120 in FIG. A streak image is formed on the fluorescent surface 109 by the dotted electron beam.

FIG. 5 is a perspective view showing still another embodiment of the entrance window.

This embodiment is also applied to the streak tube described above in the same manner as described above.

Ten glass fibers 151 having the same shape as the glass fiber 131 shown in FIG. 3 are arranged at intervals of 0.5 mm in the direction perpendicular to the direction of sweep of the streak tube.

The glass fiber 151 is formed by dividing the entrance window 104, forming grooves corresponding to the glass fiber 151 on the end faces of the divisions, and then sandwiching and welding them.

An electrode thin film and a photocathode are formed in the same manner as in the case of FIG.

Similarly, the distance between the photocathode and the mesh electrode is about 2 mm.

As in the first embodiment described above, the electric field on the surface of the photocathode can be easily increased.

Ten streak images are obtained on the fluorescent surface 109 by the ten electron beams.

FIG. 6 is a perspective view showing still another embodiment of the entrance window. This embodiment is also applied to the streak tube described above in the same manner as described above.

The front surface of the entrance window 101 is formed from a fiber plate with a pitch of 5 μm, and the center of the inner surface of the entrance window
A 10 mm x 500 μm portion protrudes toward the mesh electrode by a height of 200 μm, and the surface of the tip is 10 mm.
×200 μm.

An electrode thin film and a photocathode are formed in the same manner as in the case of FIG.

Similarly, the distance between the photocathode and the mesh electrode is about 2 mm.

The longitudinal direction of the photocathode is perpendicular to the sweeping direction of the streak tube. As in the first and second embodiments described above, the electric field on the surface of the photocathode can be easily increased.

A linear electron beam is swept from top to bottom on the fluorescent surface 109 to form a streak image.

As shown in each of the above embodiments, when the photocathode portion is made to protrude, the electric field on the surface of the photocathode can be increased, so that the temporal resolution and red sensitivity of the streak tube can be improved.

Although the area of the photocathode is smaller than that of conventional phototubes, the dark current may become large.

This problem can be solved by using:

Between the photocathode and the mesh, for example, 500V is applied with positive polarity on the mesh side only during the period of sweeping on the fluorescent surface, for example, 5 ns, and 0V is applied at other times.

In this way, the dark current contributes to the background only during the sweep, so the influence of the dark current can be extremely reduced.

In a conventional streak tube (one without a protruding photocathode), in order to generate a high electric field of 3KV/mm as mentioned above, it is necessary to
Although it is necessary to apply a voltage of 6 KV, it is difficult to apply such a large amplitude voltage for a short period of time (for example, 5 ns).

(Effects of the Invention) As described above in detail, the streak tube according to the present invention has a protrusion formed on a part of the inner surface of the entrance window, and an electrode thin film connected to an external circuit on the surface of the protruding end of the protrusion. , and the photocathode is arranged closest to the accelerating electrode facing the inner surface of the entrance window. The electric field can be easily increased.

Furthermore, since a large electric field can be generated by applying a relatively low voltage, it can be driven and used so as to give a sharp change in the electric field only for a necessary extreme time.

As a result, it is possible to obtain a streak tube that has high temporal resolution and high red sensitivity, and does not cause background rise or white spots.

As described above, since the amplitude of the pulse voltage when performing the gate operation can be reduced, the gate voltage generation circuit can be simplified.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a first embodiment of a streak tube according to the present invention, taken along a plane that includes the tube axis and is parallel to the deflection electrode. FIG. 2 is a cross-sectional view of the streak tube taken along a plane perpendicular to the deflection electrode. FIG. 3 is an enlarged sectional view showing the relationship between the central part of the entrance window and the accelerating electrode in the first embodiment. FIG. 4 is a schematic diagram for explaining the electric field enhancement effect. FIG. 5 is a perspective view showing still another embodiment of the entrance window. FIG. 6 is a perspective view showing still another embodiment of the entrance window. FIG. 7 includes a tube axis showing the configuration of a conventional streak tube,
FIG. 3 is a cross-sectional view taken along a plane parallel to the deflection electrodes. FIG. 8 is a cross-sectional view of the conventional streak tube taken along a plane that includes the tube axis and is perpendicular to the deflection electrode. FIG. 9 is a graph showing the relationship between the electric field between the photocathode and the mesh electrode and the wavelength sensitivity of the photocathode. FIG. 10 is a graph showing the relationship between accelerating electric field and dark current in a conventional streak tube. 101...Entrance window, 102...Output window, 103
...Vacuum-tight container, 104...Photocathode, 105...
...Mesh electrode, 106... Focusing electrode, 107...
...Aperture electrode, 108...Deflection electrode, 109
... Fluorescent surface, 131 ... Glass fiber, 132
... Electrode thin film, 134 ... Photocathode, 151 ... Protruding row of glass fibers, 161 ... Linear protrusions of glass fibers.

Claims (1)

[Scope of Claims] 1. A streak tube having a photocathode formed on the inner surface of an entrance window and an electrode for accelerating and deflecting photoelectrons generated by the photocathode, comprising: a protrusion formed on a part of the inner surface of the entrance window; A photocathode is formed on the surface of the protruding end of the protrusion through an electrode thin film connected to an external circuit, and the photocathode is disposed closest to the acceleration electrode disposed facing the inner surface of the entrance window. A streak tube that accelerates photoelectrons with an acceleration electrode and deflects them with a deflection electrode. 2. A streak tube in which photoelectrons are accelerated by an accelerating electrode and deflected by a deflection electrode, as set forth in claim 1, wherein the protrusion is a glass fiber provided at the center of the entrance window and extending to the surface of the entrance window. 3. The protrusions are glass fibers arranged on the entrance window at intervals in a direction perpendicular to the sweep direction, and each extending to the surface of the entrance window. A streak tube that is accelerated and deflected by a deflection electrode. 4. Accelerating photoelectrons with an accelerating electrode according to claim 1, wherein the protrusions are glass fibers arranged in the entrance window in a band shape in a direction perpendicular to the sweep direction, each extending to the surface of the entrance window. , a streak tube deflected by a deflection electrode. 5. An airtight container having an entrance window, a protrusion formed on a part of the inner surface of the entrance window, and a photocathode formed on the surface of the protruding end of the protrusion via an electrode thin film connected to an external circuit. an accelerating electrode for rapidly accelerating the photoelectron beam emitted from the photocathode in the direction of the output screen; a focusing electrode for refocusing the photoelectron image emitted from the photocathode onto the output screen; A streak tube consisting of an anode electrode having an aperture, a deflection electrode for sweeping the photoelectron beam on an output screen, a phosphor screen for forming an output image, and an output window with the phosphor screen provided on the inner surface. and a means for applying a pulse-like accelerating voltage to the accelerating electrode in the acceleration direction so that the photoelectrons reach the screen only when the photoelectron beam is swept. Device.