JPH0831308B2 - Image tube with built-in microchannel plate - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an image tube with a built-in microchannel plate, which has a built-in microchannel plate for multiplying the electrons generated on the photocathode for each channel and making them incident on the phosphor screen, and in particular, to an image intensifier. The present invention relates to an image tube with a built-in microchannel plate, which is suitable for use in an image tube for weak light and a streak tube, etc., which causes less background rise and crosstalk.

[Prior art]

Image tubes include one that converts an image of infrared rays or X-rays that cannot be seen directly by a person into an image of visible light, and one that enhances a weak light image. One of them is, for example, There is a proximity type image tube as shown in the figure. In this proximity type image tube, a photoelectric surface 12 is formed on the inner surface, for example, an input face plate 10 made of a glass plate or a fiber optic plate, and a fluorescent surface 16 is formed on the inner surface, for example, a glass plate or a fiber optic. The output face plate 14 made of a plate is disposed so as to face each other,
Predetermined spacing by the annular insulator 18, for example the photocathode 12 and the phosphor screen
It is vacuum-tightly sealed with a distance of 16 to 1 mm. During operation of this image tube, a high voltage of, for example, 10 KV is applied to the phosphor screen lead 22 with respect to the photocathode lead 20. In this state, input light is irradiated from the direction of the arrow, and when a photo image is formed on the photocathode 12, photoelectrons are emitted. The photoelectrons are accelerated in the direction perpendicular to the photocathode 12 by a strong electric field and reach the fluorescent screen 16, which causes the fluorescent screen 16 to emit light and reproduces the enhanced optical image. Between the photocathode 12 and the phosphor screen 16, an electron lens for focusing photoelectrons is not provided, the spread of the photoelectrons is limited by a strong parallel electric field, and the resolution is maintained. The feature is that it is small and has no image distortion. In such an image tube, as shown in FIG. 10, in order to prevent the light generated from the phosphor screen 16 from being fed back on the photocathode 12 to cause a photoelectron flow unrelated to the image and to be buried in the image, , A phosphor layer 23 forming the phosphor screen 16
A metal back layer 24 for light shielding is applied to the surface of the. The metal back layer 24 is usually formed of an aluminum thin film having good electron transparency. Further, the light transmitted through the photocathode 12 is diffusely reflected by the metal back layer 24 of the phosphor screen 16 and re-enters the photocathode 12 to emit photoelectrons, thereby raising the back ground and crosstalk. To prevent the photocathode
In an image tube in which a microchannel plate or the like is not disposed between 12 and the fluorescent surface 16, especially in the proximity type image tube as described above, a layer having a low reflectance for light is provided on the metal back layer 24. It is proposed to provide the
58-225548, JP-A-59-114738, JP-A-59-189544
issue). On the other hand, as the image tube, in addition to the image tube which does not use a micro channel plate (hereinafter abbreviated as MCP) such as the proximity type image tube as described above, electrons generated in the photocathode are collected by a minute channel. There is an image tube for weak light (such as an image intensifier) and a streak tube with a built-in microchannel plate for multiplying and entering the fluorescent screen. Also in this MCP built-in image tube and streak tube, when strong light is incident on one point of the effective photocathode, an output light image is obtained at a position on the phosphor screen 16 of the output faceplate 14 corresponding to the incident point, In addition to that position, the area around it became brighter, and there was back ground rise and crosstalk. However, unlike the image tube that does not have a built-in MCP such as the proximity type image tube as shown in FIG.
Is inserted, the light diffusely reflected by the metal back layer 24 of the phosphor screen 16 does not enter the photocathode 12 again.
Therefore, in the past, the cause of the background rise and crosstalk in the MCP built-in image tube was unknown, and effective measures were not taken.

[Problems to be achieved by the invention]

An object of the present invention is to suppress back ground rise and crosstalk generation in an MCP built-in image tube.

[Means for achieving the object]

The present invention, in an image tube with a built-in microchannel plate in which a microchannel plate for multiplying electrons generated on a photocathode and entering the phosphor screen by each channel is made to face the microchannel plate, The above object is achieved by providing a layer having a low reflectance for electrons on the surface of the phosphor screen. In addition, a layer having a low reflectance for the electrons is at least 1
It is a light element layer of the layer. Alternatively, the low electron reflectance layer is at least one porous layer.

[Action and effect]

In the present invention, the inventors conducted a detailed experiment on the cause of the rise in the background and the crosstalk of the MCP built-in image tube, the cause of which was unknown, and the cause was clarified, and the countermeasure was taken. Is. That is, the inventors of the present invention accurately measured the luminance distribution on the output fluorescent surface of the streak tube having the built-in MCP, and found that the distribution indicated by the solid line in FIG. Furthermore, as a result of investigating by what mechanism this back ground rise occurs, as shown in FIG.
A part of the multiplied signal electron group from P30 is reflected by the metal back layer 24 on the surface of the fluorescent screen 16, and this is again returned to the MCP30.
-It was found that this is because the reverse electric field between the phosphor screens 16 pushes it back to the phosphor screen 16 side to flow into the phosphor screen 16. That is, since the reflection of electrons by the fluorescent screen 16 is close to scattering and is reflected in various directions, the position at which the electrons flow into the fluorescent screen 16 again is distributed widely, centering on the original signal current incident position, Second
It was found that the distribution shown by the solid line in the figure was obtained. The present invention has been made based on the results of the above-mentioned researches by the inventors, and as shown in FIG. 1, a phosphor screen 31 (including a phosphor layer 23 and a metal back layer 24) facing the MCP 30.
By providing a layer 32 having a low reflectance for electrons on the surface of the, the reflection of incident electrons by the fluorescent surface 31 and the fluorescent surface
It suppresses the re-inflow into 31, and suppresses the rise of the background and the occurrence of crosstalk.

【Example】

Hereinafter, embodiments of the present invention applied to a streak tube with a built-in MCP will be described in detail with reference to the drawings. As shown in FIG. 4, the first embodiment of the present invention has a built-in MCP 30 for multiplying the electrons generated on the photocathode 12 for each minute channel and making the electrons enter the phosphor screen 31 as shown in FIG. M
It was applied to a streak tube with a built-in CP, and as shown in detail in FIG. 5, the phosphor screen 31 (fluorescent material layer 2) facing the MCP30 was used.
3 (including the metal back layer 24) and a carbon (C) thin film 34 of a light element having a low reflectance for electrons is formed on the surface of the metal. In FIG. 4, 42 is a reticulated accelerating electrode for accelerating the electron image generated on the photocathode 12, 44 is a focusing electrode for focusing the electrons accelerated by the accelerating electrode 42 within a certain range, 46
Is an aperture electrode (anode) for further accelerating the electrons, and 48 and 50 are deflection plates for rapidly sweeping the electrons passing through the aperture electrode 42 in the vertical direction and the direction perpendicular to the paper surface of the drawing, respectively. The electron image deflected by the deflecting plates 48 and 50 is again converted into an optical image on the fluorescent screen 31 (a streak image which is a luminance information image in which the passage of time is represented by the position in the vertical axis direction). It is supposed to be converted. As shown in detail in FIG. 5, the phosphor screen 31 according to the present invention comprises a phosphor layer 23 formed on the output face plate 14, an aluminum metal back layer 24, and a carbon thin film 34. The phosphor layer 23 is formed by stacking several layers of phosphors having a particle size of several micrometers by a centrifugal method or the like. The aluminum metal back layer 24 is the phosphor layer.
Aluminum on 23, about 300 angstroms,
It is said to have been vacuum-deposited. The carbon thin film 34 is formed by depositing carbon on the metal back layer 24 for about 300 ang stroke by, for example, a sputtering method. FIG. 6 shows an example of the light emission distribution on the output phosphor screen when light is incident on one point on the photocathode 12 of the streak tube 40 according to the present embodiment. As is clear from the figure, the background was reduced to about 1/4 of that of the conventional light emission distribution shown in FIG. 2, and it was confirmed that a large improvement was observed. In this example, the light element forming the low reflectance layer was carbon, but the kind of the light element is not limited to this, and for example, beryllium may be used. Next, a second embodiment of the present invention will be described in detail. In this embodiment, as shown in FIG. 7, the fluorescent surface 52 facing the MCP 30 is used.
Is composed of a phosphor layer 23 formed on the output face plate 14, an aluminum metal back layer 24, and a porous layer 53. The porous layer 53 is formed by first depositing aluminum in an inert gas, then removing the gas, and then depositing aluminum in a high vacuum to form a porous aluminum layer having a thickness of about 300 Å. Layers have been formed. Since the other points are the same as those of the first embodiment, the description thereof will be omitted. In the present embodiment, the surface of the phosphor screen 52 is the aluminum porous layer 53, and aluminum is vapor-deposited on the surface in a high vacuum degree. Therefore, the porous aluminum is the aluminum thin film of the substrate ( 24), the particles are strongly bound to each other, and the connection strength between particles is increased, so that they are not easily peeled off and the stability is improved. That is, the aluminum vapor deposition layer formed in the inert gas atmosphere occludes the inert gas, and this is gradually released into the vacuum during the operation of the streak tube 40, which causes deterioration of the characteristics of the streak tube. However, by vapor-depositing aluminum on the surface in this way, outgassing is suppressed and favorable results are obtained. Next, a third embodiment of the present invention will be described in detail. In this embodiment, as shown in FIG. 8, a phosphor screen 54 facing the MCP 30 is provided with a phosphor layer 23 formed on the output face plate 14.
It is composed of an aluminum metal back layer 24, and a carbon porous layer 55 and an aluminum thin film 56 which are alternately stacked on the metal back layer 24. The porous layer 55 is formed of carbon, for example, by a sputtering method. The aluminum thin film 56 is formed by performing vapor deposition in a high vacuum degree, and the uppermost surface is the aluminum thin film 56. Also in this example, since the uppermost surface is an aluminum thin film formed by vapor deposition, gas release from the porous layer 55 is suppressed, and a desirable result is obtained. Further, since carbon easily adsorbs the alkali metal forming the photocathode 12, a large amount of the adsorbed alkali metal may damage the phosphor (23) at a high temperature. By stacking the aluminum thin film 56 on the porous layer 55, the fluorescent screen 54 can be protected. In each of the above embodiments, the present invention is applied to a streak tube, but the scope of application of the present invention is not limited to this, and general image tubes with a built-in MCP, such as image intensifier and high speed, are used. It is obvious that the same can be applied to the response photomultiplier tube and the like. Of course MCP is 2
For example, the invention can be similarly applied to an image tube built in a tandem type.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a structure of a phosphor screen portion of an MCP built-in image tube according to the present invention, and FIG. 2 is a luminance on an output surface when a point light is incident on a conventional MCP built-in streak tube. Fig. 3 is a diagram showing an example of distribution, Fig. 3 is a cross-sectional view for explaining a mechanism in which the back ground is raised in an MCP built-in image tube discovered by the inventors, and Fig. 4 is a MCP built-in type according to the present invention. First streak tube
FIG. 5 is a cross-sectional view showing the overall structure of the embodiment, FIG. 5 is a cross-sectional view showing the structure of the phosphor screen portion of the first embodiment, and FIG. 6 is an output surface when point light is incident on the first embodiment. FIG. 7 is a sectional view showing the configuration of the phosphor screen portion of the second embodiment of the present invention, and FIG. 8 is a sectional view showing the configuration of the phosphor screen portion of the third embodiment. FIG. 9 is a cross-sectional view showing the structure of a conventional proximity image tube, and FIG. 10 is a cross-sectional view for explaining the mechanism of back ground generation in the proximity image tube. 12 ... Photocathode, 31, 52, 54 ... Phosphor screen, 23 ... Phosphor layer, 24 ... Metal back layer, 30 ... Micro channel plate (MCP), 32 ... Low reflectance layer, 34 ... Carbon thin film, 40 …… streak tube, 53, 55 …… porous layer, 56 …… aluminum thin film.

Claims (3)

[Claims] 1. An image tube with a built-in microchannel plate, in which a microchannel plate for multiplying electrons generated on a photocathode and making them incident on a phosphor screen is incident on a fluorescent surface, facing the microchannel plate. An image tube with a built-in microchannel plate, characterized in that a layer having a low reflectance for electrons is provided on the surface of said phosphor screen. 2. An image tube with a built-in microchannel plate according to claim 1, wherein the layer having a low reflectance for electrons is at least one light element layer. Type image tube. 3. An image tube with a built-in microchannel plate according to claim 1, wherein the layer having a low reflectance for electrons is at least one porous layer. Image tube with built-in plate.