Method for converting images of external energy effects into an electric signal and electron-beam vacuum device

Abstract

 An image of external radiation is recorded onto an amplifying microchannel plate (3) connected to a supply voltage source (4) and is read from the side opposite the record side by scanning with an electron beam at current strength, providing the introduction of the plate channels in the saturation condition, and the recording of the image on a flat collecting electrode (5) made as a fine-structured grid and disposed at the readout side of the microchannel plate.

Description

[0001] This invention relates to an apparatus and method in electronic engineering and may be useful for converting external radiation into an electric signal.

[0002] A method has previously been proposed for converting images of external energy effects into an electric signal, comprising the steps of recording images of the external energy effect upon an amplifying microchannel plate connected to a supply voltage source, when the directions of amplification in the plate channels coincide with the direction of entry of the external radiation, and readout of the record of external radiation image by the electron beam scanned over the plate surface in a rectangular raster when current strength corresponds to the saturation conditions of the plate channels, with the record of the output signals on the collecting electrode disposed at the plate side opposite the record side when scanning the plate by the electron beam current being realized from the record side (SU,N 693482, Int.Cl. H01J 31/58, 1982).

[0003] An electron-beam vacuum device for converting images of external energy effects into an electric signal is also publicly known, said device comprising a housing provided with an input window transparent for the external radiation and contacts for connection to voltage sources, an amplifying microchannel plate incorporated inside the housing, a flat collecting electrode disposed behind the microchannel plate and an electron gun for generating a scanning beam and a deflection system for providing a retangular scanning raster over the plate surface, disposed at the side of input window, said device realising the above-mentioned method (SU, N° 693482).

[0004] However, the known method and the device give some distortion when converting images of external radiation and there is limitation of the device functionality by the pulse mode of recording and readout.

[0005] Objects of the present invention are to eliminate the distortion of record of the external radiation image when reading the latter and to widen the functionality due to the provision of continuous modes of recording and readout in addition to the pulse mode.

[0006] To achieve these objects, in a method of converting images of external radiation into an electric signal, comprises the recording an image of the external radiation upon an amplifying microchannel plate connected to a supply voltage source, when the directions of amplification in the plate channels coincide with the direction of entry of the external radiation, and readout of the record from the plate when scanning it with an electron beam current, the strength of which corresponds to the saturation conditions of plate channels, and recording the output signals on a collecting electrode, disposed at the plate side opposite the record side, characterized by scanning the plate by the electron beam from the side of the collecting electrode with an amount of energy at which the secondary electron-emission coefficient exceeds 1.

[0007] This allows elimination of the distortions of the recording of external radiation images and widening of the functionality due to the provision of both the pulse mode and the continuous mode of recording and readout with decreasing an angle between the axes of plate channels and scanning beam and with absence of crossover of the trajectories of the beam being recorded and the scanning beam with the use of amplifying microchannel plate as a two-sided storage target.

[0008] In a preferred embodiment of the invention the scanning beam is directed onto the plate surface in such a manner that the depth of its penetration into the plate channels is equal to 0.1-0.5 the plate thickness.

[0009] With the depth of beam penetration into the plate channels being constant within the mentioned range this allows use of the plate amplifying properties during scanning and provision of constant conditions of electron bean interaction with the walls of plate channels and constant value of the secondary electrons amplification in the backward direction when generating a resultant beam used during the electric signal generation.

[0010] The method provides for the possibility of realization of an analog mode of converting an external radiation image when recording is carried out with the intensity maximum level of which during the record operation within the limits of a diameter of scanning beam corresponds to the inequality:

where q_max is the maximum record level, in C;

C is a plate capacity, in F;

U is supply voltage of the plate, in V;

n is a number of plate channels within the limits of a diameter of scanning beam;

N is a total number of plate channels;

k is an amplification coefficient of the plate;

γ is a coefficient of recording efficiency of the external radiation by the microchannel plate;

preferably with minimum level during the record operation within the limits of a diameter of scanning beam which corresponds to the inequality:

where q_min is the minimum record level, in C;

this corresponds to the number of television system gradations; or realization of the mode of converting the external radiation image by analogy with the newspaper mode of image reproduction, when recording is carried out with the intensity maximum level of which during the record operation within the limits of a diameter of scanning beam corresponds to the inequality:

where q_1max is the maximum record level, in C;

and preferably with minimum level during the record operation within the limits of a diameter of scanning beam which corresponds to the equation:

where q_1min is the minimum record level, in C.

[0011] Alternatively, the method may provide for scanning the plate by the electron beam swept over its surface in a raster, which allows realization of recording the external radiation and its readout in a pulse mode; in the optimum embodiment in order to maintain the potential relief of record the duration of the scanning frame of a raster is given according to the inequality:

where

t_k is a duration of the scanning frame of a raster, in S;

R is a plate resistance in Ω;

[0012] the duration of the record process is set ≤ 0.1 t_k and the time interval of switching on the scanning raster is set exceeding the record time by ≤ 0.01 t_k, and that it is desirable for decreasing the power consumption to apply voltage to the amplifying microchannel plate in a pulse mode only for a period from the beginning of recording external radiation till the termination of its readout from the plate and it is most preferable in order to diminish the influence on the other devices and the environment to apply constant voltage being equal to 0.5-0.7U to the microchannel plate for the intervals between the pulses of supply voltage application.

[0013] In the same case, alternatively, the method may provide for realization of external radiation record in a continuous mode and its readout from the amplifying microchannel plate by the single scanning raster or continuously when the time of the scanning frame of a raster is given according to the inequality:

   where t_1k is the time of frame sweep of the scanning raster, in S.

[0014] In a preferred embodiment of the invention it is possible to carry out recording images of the external radiation onto the amplifying microchannel plate after the preliminary conversion into radiation in the range of its sensitivity, which allows widening of the functionality of the method due to the expansion of the frequency range of the images being recorded.

[0015] The object of the invention is also attained in that an electron-beam vacuum device for converting images of external radiation into an electric signal, comprises a housing provided with an input window transparent for the external radiation and contacts for connecting to voltage sources, an amplifying microchannel plate incorporated inside the housing, a flat collecting electrode disposed behind the plate, an electron gun for generating a scanning bean and a deflection system for providing a scanning raster over the plate surface, and further comprising a fine-structured grid placed behind the collecting electrode made as a fine-structured grid, said electron gun and a deflection system being disposed behind the collecting electrode and the fine-structured grid, and the the amplifying microchannel plate, the collecting electrode and the fine-structured grid being positioned in parallel and coaxially and it being desirable that their operating zones are of the same form corresponding to the form of the scanning raster.

[0016] Such a construction of the device allows to use the amplifying microchannel plate to be used as a two-sided storage target both in the pulse mode and in the continuous mode of recording and readout and eliminates the distortions when reading the record of external radiation image from the plate due to the absence of crossover of the beam being recorded with the scanning beam.

[0017] In a preferred embodiment of the invention the device is equipped with a film photocathode having sensitivity in the ranges of roentgen and/or ultraviolet radiation and disposed on the input surface of the amplifying microchannel plate.

[0018] This allows performance of the device to be provided in the above-mentioned ranges of the external radiation without generating the distortions when reading owing to the external radiation of the other ranges to which the device becomes insensitive.

[0019] In another preferred embodiment of the invention the device is provided with the film photocathode having sensitivity in the ranges of visible and/or near ultraviolet and/or near infrared radiation and disposed on the inner surface of the housing input window and also with a continuous metal film positioned on the input surface of the amplifying microchannel plate, said film being transparent for photoelectron current and is not being transparent in the range of photocathode sensitivity.

[0020] This allows performance of the device to be provided in the range of photocathode sensitivity.

[0021] It is also possible to equip the device with the amplifying microchannel plate with the gauge of 60-120. This permits the sensitivity of the device to be increased to the external radiation providing the saturation mode of the plate channels when at least one electron hits into them.

[0022] By way of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which:-

Fig. 1 is a schematic illustration of an embodiment of electron-beam vacuum device for realization of the method, in accordance with the present invention;

Fig. 2 shows a fragmentary view of the device of Fig. 1 provided with a film photocathode; and

Fig. 3 shows a fragmentary view of the device of Fig. 1 provided with a film photocathode and a metal film.

[0023] The electron-beam vacuum device for converting images of the external radiation into an electric signal comprises a housing 1 provided with an input window 2 transparent for the external radiation, and the following elements disposed coaxially in the housing 1 in succession in the direction from the window 2: an amplifying microchannel plate 3 with preferred gauge of 60-120 connected to a supply voltage source 4, a flat collecting electrode 5 connected through a resistor 6 to a voltage source 7 and made as a fine-structured grid, a fine-structured grid 8 connected to a voltage source 9, a deflection system 10 for generating upon the plate surface 3 a scanning raster, for example a rectangular one, by an electron beam generated by an electron gun 11. The plate 3, the collecting electrode 5 and the fine-structured grid 8 are positioned in parallel and their operating zones have, for example, a rectangular form with dimensions corresponding to the rectangular scanning raster generated by the beam of the deflection system 10 of the electron gun 11.

[0024] For recording images of the external radiation in the ranges of roentgen and/or ultraviolet radiation the device is provided with a film photocathode 12 disposed on the input surface of plate 3 and having sensitivity in the range of radiation being registered.

[0025] For recording images of the external radiation in the ranges of visible and/or near ultraviolet and/or near infrared radiation the device is provided with a film photocathode 13 disposed on the inner surface of the input window 2 and having sensitivity in the range of radiation being registered and with a continuous metal film 14 which is transparent for the photoelectron current and non-transparent in the range of photocathode 13 sensitivity and disposed on the input surface of the amplifying microchannel plate 3.

[0026] The proposed method is realized in the described device in the following way.

[0027] The image of the external energy effect in the form of radiation in the range of infrared, visible, ultraviolet or roentgen radiation passes into the housing 1 through the window 2 and acts upon the amplifying microchannel plate 3. For recording images of the external radiation to which the plate 3 is insensitive, the external radiation is passed through the film photocathode 12 or film photocathode 13 and a metal film 14, thus being converted into the photoelectron current. When interacting with the plate 3 the beams of the external radiation images or the photoelectron current produced by them when passing through the photocathode 12 or 13, provided that the directions of entry of the external radiation coincide with the direction of amplification in the plate 3 channels, generate positive charges in the channels, especially in their output part. Record of the image may be carried out according to the conditions (1) and (2) or (3) and (4), that is in an analog or non-analog mode. In case the condition (1) and preferably the condition (2) are satisfied the input energy effect produces a positive charge in each channel of the plate 3 which is proportional to the input intensity. When the condition (3) and preferably the condition (4) are satisfied the plate 3 with the gauge 60-120 is generally used and the presence of input signal in the section of plate 3 channel disposition guarantees introduction of the channel in the saturation condition and sharp decrease of the amplification coefficient in the section of said channel. In this case the potential relief corresponding to the image of the input signal is defined by the position of the plate 3 channels introduced in the saturation condition. The potential relief of the input signal record in a pulse mode of operation is maintained on the walls of the plate 3 channels during the period of resetting of the initial distribution of charges which is defined by the resistance and capacity of the plate 3 and usually equals 10⁻-10⁻¹ s, this being sufficient for a single readout.

[0028] For readout of the record of the external radiation image by the electron gun 11 the electron beam is generated with current strength corresponding to the saturation conditions of the plate 3 channels. The deflection system 10 creates from this beam a readout raster,for example a rectangular one, on the plate 3 surface which scans the latter. The collecting electrode 5 made as a fine-structured grid and the fine-structured grid 8 are transparent for the electron beam of the gun 11 and do not hinder its passage to the plate 3 surface. Besides, the fine-structured grid 8, to which voltage is applied from the source 9, together with the electrodes of the gun 11 provides an electric field changing the trajectory of the scanning beam for provision of the depth of penetration into the plate 3 channels being equal to 0.1-0.5 the plate 3 thickness and defining the optimum conditions of reading the potential relief of the input signal record. The amplification coefficient of the plate 3 defines the type of potential relief record, therefore the output current from the plate 3 is modulated according to the potential relief of record of the input signal image and its strength is proportional to the residual electron current of the scanning beam, which is not used for creation of the saturation condition for the plate 3 channels which have already bean introduced into such a condition. The electron current generated when scanning the plate 3 surface is trapped by the collecting electrode 5 under the action of the potential of the source 7. Electrons which have passed through the collecting electrode 5 are retarded by the electric field of the fine-structured grid 8 and are directed back onto the collecting electrode 5. The output electric signal is generated on the resistor 6, connected into the circuit of the collecting electrode 5, by analogy with that in a television electron- beam tube.

[0029] In a pulse mode of the device operation the voltage from the source 4 is applied to the plate 3 continuously or by pulses during the recording image of the external radiation and its readout and in the intervals between the pulses preferably voltage being equal to 0.5-0.7U is applied at which the amplification coefficient of the plate 3 is close to 1. This minimizes during the operation the level of radio interferences influencing the environment and the other electronic devices. In this case the satisfaction of the condition (5) and the conditions of the record process duration and switching duration of the scanning raster allows during the period of readout the potential relief of the input signal record to be maintained unchangeable or when diminishing it up to 10% on the last lines of a raster allows the introduction of a correcting action by the external machinery means of processing.

[0030] In a continuous mode of the device operation the satisfaction of the condition (6) provides resetting the plate 3 channels introduced in the saturation condition to the initial condition when applying a supply voltage from the source 4 during the period t_1k. This allows the obtaining of an image only of the external radiation without any traces of the scanning beam during the repeat readout of the potential relief from the same section of the plate 3.

Example

[0031] The device for converting an image of the external radiation into an electric signal is provided with the amplifying microchannel plate with a diameter of 34 mm and a channel diameter of 10µm; the coefficient of the usable area of the plate is equal to 0.6, resistance is 5.10⁸ Ω, capacity is 10 pF; amplification coefficient is equal to 10⁴ at the supply voltage of 1kV. The electron gun and the deflection system generate the scanning raster with 300 reading lines; the duration of the frame sweep is equal to 25·10⁻³s; the duration of the line is 65 µs. The current density of the reading beam of a raster is constant and a diameter is 60 µm. It is calculated according to the given data that 21 plate channels are present within the limits of the reading beam diameter, i.e. of the image element. The resistance of a resistor in the circuit of the collecting electrode and the capacities of the collecting electrode and the input amplifier define the frequency band of the input circuit transmission, specified by the data of the scanning raster, therefore at a given total capacity of the collecting electrode and the input amplifier, being equal to 10 pF, the resistance value of a resistor is 3 kΩ. In such a device in a continuous mode of record and readout the output signal amplitude is 0.3. mV for the maximum level of record when reading and it is 1 mV for the minimum level of record.

[0032] Thus, in the absence of distortions during the conversion the proposed method and the device provide the possibility of realization of the recording and readout of the image of the external radiation both in a pulse mode and in a continuous mode.

Claims

1. A method for converting images of external radiation into an electric signal, comprising recording an image of the external radiation upon an amplifying microchannel plate (3) connected to a supply voltage source (4), when the directions of amplification in the plate channels coincide with the direction of entry of the external radiation, and reading out the recording of the external radiation image from the plate by scanning it with an electron beam current, the strength of which corresponds to the saturation conditions of the plate channels, and recording the output signals on a collecting electrode (5) disposed at the plate side opposite the recording side, characterized in that the scanning of the plate by the electron beam is realized from the side of the collecting electrode with an amount of energy at which the secondary electron-emission coefficient exceeds 1.

2. A method according to claim 1 characterized in that the scanning beam is directed onto the plate surface in such a manner that the depth of its penetration into the plate channels is equal to 0.1-0.5 the plate thickness.

3. A method according to claims 1 or 2, characterized in that the recording is carried out with an intensity maximum level which during the record operation within the limits of a diameter of scanning beam corresponds to the inequality:

where

qmax is the maximum record level in C;

C is a plate capacity in F;

U is supply voltage of the plate in V;

n is a number of plate channels within the limits of a diameter of scanning beam;

N is the total number of plate channels;

k is an amplification coefficient of the plate;

y is a coefficient of recording efficiency of the external radiation by the microchannel plate.

4. A method according to claim 3, characterized in that the recording is carried out with an intensity minimum level which during the record operation within the limits of a diameter of scanning beam corresponds to the inequality:

where

qmin is the minimum record level in C;

qmax is the same as mentioned above.

5. A method according to claims 1 or 2, characterized in that the recording is carried out with an intensity maximum level which during the record operation within the limits of a diameter of scanning beam corresponds to the inequality:

where

q1max is the maximum record level in C;

C,U,n,N,k,y are the same as mentioned above.

6. A method according to claim 5, characterized in that the recording is carried out with an intensity minimum level which during the record operation within the limits of a diameter of scanning beam corresponds to the inequality:
where q1min is the minimum record level in C.

7. A method according to any of the claims 1 to 6, characterized in that scanning the plate is realized by the electron beam swept over its surface in a raster.

8. A method according to claim 7, characterized in that the recording of the image of the external radiation and its readout from the plate are realized in a pulse mode, and that the duration of the scanning frame of a raster is given according to the inequality:

where

t_k is a duration of the scanning frame of a raster in s;

R is a plate resistance in Ω;

C is the same as mentioned above;

the duration of the record process is set ≤0.1t_k and the time interval of switching on the scanning raster is set to exceed the record time by ≤0.01t_k.

9. A method according to claim 8, characterized in that supply voltage is applied to the amplifying microchannel plate in a pulse mode only for a period from the beginning of recording the image of the external radiation till the termination of its readout from the plate.

10. A method according to claim 9, characterized in that constant voltage equal to 0.5-0.7U is applied to the microchannel plate for the intervals between the pulses of supply voltage application.

11. A method according to claim 7, characterized in that the recording the image of the external radiation is carried out in a continuous mode.

12. A method according to claim 11, characterized in that the readout of the record of the external radiation image from the amplifying microchannel plate is carried out in a continuous mode and the time of the scanning frame of a raster is given according to the inequality:

where

t_1k is the time of frame sweep of the scanning raster in s;

R,C are the same as mentioned above.

13. A method according to claim 11, characterized in that the readout of the record of the external radiation from the amplifying microchannel plate is carried out by the single scanning raster.

14. A method according to any of the claims 1 to 13, characterized in that recording the image of the external radiation is carried out after the preliminary conversion into radiation in the range of sensitivity of the amplifying microchannel plate.

15. An electron-beam vacuum device for converting images of the external radiation into an electric signal, comprising a housing (1) provided with an input window (2) transparent for the external radiation and contacts for connecting to voltage sources (4,7,9), an amplifying microchannel plate (3) incorporated inside the housing, a flat collecting electrode (5) disposed behind the plate, an electron gun (11) for generating a scanning beam and a deflection system (10) for providing a scanning raster over the plate surface, said device further comprising a fine-structured grid (8) placed behind the collecting electrode made as a fine-structured grid, said electron gun (11) and said deflection system (10) being disposed behind the collecting electrode and the fine-structured grid, and the amplifying microchannel plate (3), the collecting electrode (5) and the fine-structured grid (8) being positioned in parallel and coaxially.

16. A device according to claim 15, characterized in that the amplifying microchannel plate (3), the collecting electrode (5) and the fine-structured grid (8) have identical operating zones corresponding to the form of the scanning raster.

17. A device according to claims 15 or 16, characterized in that it is provided with a film photocathode (12) having sensitivity in the ranges of roentgen and/or ultraviolet radiation and disposed on the input surface of the amplifying microchannel plate (3).

18. A device according to claims 15 or 16, characterized in that it is provided with a film photocathode (13) having sensitivity in the ranges of visible and/or near ultraviolet and/or near infrared radiation and disposed on the inner surface of the housing input window and with a system transferring the photoelectron image equipped with a continuous metal film (14) positioned on the input surface of the amplifying microchannel plate, said film being transparent for photoelectron current and not being transparent in the range of film photocathode sensitivity.

19. A device according to any of claims 15 to 18, characterized in that the amplifying microchannel plate has a gauge of 60-120.

Drawing