JPS6048860B2 - Image tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image pickup tube for capturing an infrared image or a thermal image.

(Prior Art) Many proposals have been made for image pickup tubes that take infrared images.

As typical examples, an infrared vidicon using a photoconductive photocathode and a vidicon using a pyroelectric effect element as a target are known.

The pyroelectric effect is the appearance of charges in crystals that correspond to temperature changes due to heat. (Problems to be Solved by the Invention) Although the infrared vidicon using the photoconductive type photocathode is extremely effective in the near-infrared region, it is not suitable for measuring images formed by longer wavelengths. In some cases, there are problems such as the need for cooling.

Furthermore, a vidicon using a pyroelectric effect element as a target has problems such as the need to interrupt the incident infrared rays using a chopper or the like, and the imaging optical system becomes complicated. An object of the present invention is to provide an imaging tube for capturing infrared images or thermal/ray images with an extremely simple configuration using an operating principle completely different from that of already proposed infrared or thermal image capturing devices. be.

(Means for Solving the Problems) In order to achieve the above object, an image pickup tube according to the present invention includes a vacuum-tight container having an entrance window, and a surface provided on the inner surface of the entrance window that transmits infrared rays and accepts electrons. It has a shape in which a shaped electrode and a number of glass tubes are bundled together, and a layer is formed on the surface of the inner wall of each channel that has secondary electron emission characteristics and whose resistance value decreases as the temperature of that part increases. A first surface is provided at one end of the channel inner wall, a second surface parallel to the first surface is provided at the other end of each channel inner wall, and the first surface is connected to the planar J electrode. a modulator disposed in close proximity within the vacuum vessel; an electron gun disposed toward a second surface of the modulator; and an electron flow from the electron gun directed toward the second surface of the modulator. and scanning means for scanning in a sweeping manner.

(Example) Hereinafter, the present invention will be described in more detail with reference to side views and the like.

FIG. 1 is a longitudinal cross-sectional view of the image pickup tube of the present invention, in which a deflection coil and part of an output circuit are added.

A window made of a flat plate of calcium fluoride is provided on the surface forming the entrance window 2 of the cylindrical airtight container 1 made of glass to transmit infrared rays without scattering them.

On the surface of the vacuum container facing the window 2, there are lead-in wires 11 for applying an operating voltage to each electrode, which will be described later.
11 have been planted.

The planar electrode 3 is arranged parallel to the entrance window 2, and does not substantially block incident light, and can sufficiently capture signal electrons emitted from a modulator 4, which will be described later. It is formed from a mesh-like electrode with a porosity that can be used to capture images.

The modulator 4 is arranged in the vacuum vessel 1 so that its first surface is parallel to the planar electrode 3.

FIG. 2 is an enlarged end view of the modulator. In the figure, the left side is the surface facing the planar electrode, and the right side is the electron gun side, which will be described later. The basic configuration of this modulator 4 is basically the same as that of a microchannel plate known as a two-dimensional electron multiplier.

In FIG. 1, means for supplying an operating voltage to the first surface and the second surface are omitted.

The microchannel plate was invented in 1966 (Japanese Patent Publication No. 39-3871, USP 3,128,408, etc.) and has been put into practical use.

Conventional microchannel plates are widely used in applications such as amplifying electrons generated by a photocathode while maintaining their generation positions.

The microchannel plate is made of a special glass with a large number of closely spaced, uniformly density channels in a thin plate.The inner surface of the channels is activated as a secondary electron surface, and each channel acts as an independent continuous dynode. The function of

Also, the inner walls of each channel are slightly electrically conductive. The modulator 4 according to this embodiment has a channel (
A layer of lead oxide is formed on the surface of the inner wall of a thin hole (inner diameter 20).
It has a disk-like shape with approximately 600,000 micrometer-sized channels, and both end surfaces are parallel planes.

The thickness is 177177E, and electrode surfaces made of aluminum thin films are formed on two parallel surfaces.
The lead oxide layer has a secondary electron emitting ability and is endowed with relatively low electrical conductivity. However, when the temperature of the lead oxide layer increases, the resistance value of the heated portion decreases. Approximately four channels are shown in FIG. 2, cut along a plane containing the central axis of each channel.

The central axis of the channel is inclined with respect to a line connecting the center of the entrance window and an electron gun, which will be described later.

In the figure, A and b indicate an example of an infrared light path, and c indicates an example of an electron beam trajectory. Electrodes 5, 6, 7 and 8 form electrodes that accelerate the electron beam. Thermionic source 9 and the electrode 9
An electron gun is formed. A deflection coil 10 is provided outside the vacuum chamber 1 for deflecting electrons with a narrow beam diameter from the electron gun to sweep the second surface of the modulator 4.

A circuit 12 indicated by a broken line forms a circuit for supplying an operating voltage to the above-mentioned planar electrode and extracting an alternating current component of a signal modulated by the modulator 4. The following operating voltages are applied to the electrodes of each part of the image pickup tube by a circuit (not shown) and the circuit 12.

Planar electrode (mesh-like electrode) 3 ... Surface facing the planar electrode of 1260V modulator 4 ... Electron gun side surface of 1250V modulator 4 ... 250V accelerating electrodes 5 and 6 ... 250V Accelerating electrode 7...250V Electrode 8...-50V Thermionic source 9...0V The voltage of the planar electrode (mesh electrode) 3 is higher than the voltage of the opposing surface of the modulator 4 and is multiplied. The electrons are captured by the planar electrode 3.

In the state of the image pickup tube, the deflection coil 10 is driven by a drive power source (not shown), so that the electron beam of the electron gun is swept over the second surface of the modulator 4, and the entrance window 2 is opened.
An infrared image is projected onto the first surface of the modulator 4 through the optical means (not shown).

Depending on its intensity, the infrared radiation forming the infrared image heats the left-hand portion of the channel mentioned above. As a result, a temperature change corresponding to the incident infrared radiation appears in the left part of the channel. The multiplication factor for each channel of the modulator 4 is changed by this change in temperature, that is, the amount of incident infrared rays.

In other words, the multiplication factor is modulated by the infrared image. This operating mechanism will be further explained with reference to FIGS. 3 and 4. FIG. 3 is a graph showing the potential gradient within the channel of the modulator.

In the figure, the horizontal axis corresponds to the position of the channel in the tube axis direction shown in FIG. 2, and the vertical axis represents the voltage corresponding to the position.

The left end of the X-axis corresponds to the plane corresponding to the planar electrode 3 of the modulator 4, and the voltage of each channel at this point is 1250V as described above.

The right end of the X-axis corresponds to the electron gun side surface of the modulator 4, and the voltage of each channel at this point is 250V as described above.

In order to facilitate understanding, the following infrared image model will be set in relation to FIG.

Intensity unit 2 indicated by arrow a in channel 41 shown in FIG.
It is assumed that infrared rays of a single intensity position indicated by arrow b are incident on the channel 43, and no infrared rays are incident on the channel 42.

The temperature of the part of the inner wall of the channel that is irradiated with infrared rays and the area around it rises depending on the amount of infrared rays that are incident.
As described above, a lead oxide layer is formed on the inner wall surface of each channel, and since lead oxide is an n-type semiconductor, the electrical resistance decreases as the temperature increases.

Line C shown in FIG. 3 shows the potential gradient in the channel 42 where no infrared rays were incident. Since the conductivity within the channel 42 is uniform, the potential gradient is a straight line. Line B shown in FIG.
3 shows the potential gradient.

Due to the temperature rise on the side of the planar electrode 3 where the infrared rays were incident,
The resistance value decreases, resulting in a curve as shown. Similarly, since infrared rays of 2 intensity units are incident on the channel 41, the region with a lower resistance value is further expanded. FIG. 4 is a graph showing the relationship between the incident intensity of infrared rays and the electron multiplication factor when a uniform electron beam is irradiated from the second surface side of the modulator.

Each point A, B, and C shown in Fig. 4 corresponds to the channel 4 mentioned above.
Multiplication factors of 1, 43, and 42 are shown.

From this figure, it can be seen that the larger the amount of incident infrared rays is, the lower the multiplication factor is. This can be considered that as the region where the resistance value decreases becomes larger, the region where secondary electron multiplication is performed becomes shorter, and therefore the multiplication factor decreases.

The electron beams sequentially brought to different positions on the second surface of the modulator 4 by the scanning coil 10 are multiplied in the corresponding channels, and the multiplied electrons are transferred from the first surface of the modulator 4 to the planar electrodes. Reach 3.

In other words, a current corresponding to the electrons is supplied from the power supply of the circuit 12. This current causes a voltage drop in the resistor connecting the power source and the planar electrode 3, so this fluctuation is taken out to an external circuit via a capacitor.

For ease of understanding, explanations have been given in channel units, but no problem will occur even if outputs are obtained from adjacent channels simultaneously. The number of channels corresponds to the number of pixels of a conventional television system or more.

Therefore, by scanning the surface of the modulator with an electron beam of constant density and diameter using the electron gun and the deflection coil 10, an infrared image signal can be obtained from the planar electrode 3. ;(
Effects of the Invention) As explained in detail above, in the image pickup tube according to the present invention, the inner wall of the channel in a vacuum-tight container having an entrance window has secondary electron emission characteristics, and as the temperature of that part increases, the resistance value decreases. It has a built-in microchannel plate-like modulator, and is configured to extract changes in the multiplication factor of the channel using an electron beam.

Therefore, a video signal corresponding to the intensity of the infrared image can be extracted by scanning the electron beam. The structure is simple, but because it captures images by converting infrared images into changes in temperature, it is less susceptible to the effects of the wavelength distribution of infrared rays, unlike conventional infrared vidicons that use photoconductive photocathodes. Characteristics can be obtained.

Additionally, compared to the pyroelectric device described above, the imaging optical system is simpler.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a longitudinal cross-sectional view of an image pickup tube of the present invention and related circuits. FIG. 2 is a partially enlarged end view of the modulator used in the present invention, taken along a plane including the central axes of its plurality of channels. FIG. 3 is a graph showing the potential gradient within the channel of the modulator. FIG. 4 is a graph showing the modulation characteristics of the modulator. 1...Cylindrical airtight container, 2
... Entrance window of airtight container, 3... Planar electrode, 4...
・Modulator, 5, 6, 7, 8... Electrode that accelerates the electron beam, 9... Thermionic source, 8, 9... Electron gun, 10...
Deflection coil, 11...11... Lead-in wire, 12... Operating voltage supply and signal extraction circuit for planar electrode, 41, 42, 43... Channel of modulator.

Claims (1)

[Claims] 1. A vacuum-tight container having an entrance window, a planar electrode provided on the inner surface of the entrance window that transmits infrared rays and accepts electrons, and a number of glass tubes, each of which A layer is formed on the surface of the inner wall of the channel that has secondary electron emission dynamics and whose resistance value decreases as the temperature of that portion increases, and a first surface is formed at one end of the inner wall of each channel. a second surface parallel to the first surface at the other end of the
a modulator provided with a surface, the modulator being disposed in the vacuum container with the first surface close to the planar electrode;
An image pickup tube comprising: an electron gun disposed toward a second surface of the modulator; and scanning means for scanning the second surface of the modulator with an electron flow from the electron gun. 2. The image pickup tube according to claim 1, wherein the layer having secondary electron emission characteristics and whose resistance value decreases as the temperature of that portion increases is made of lead oxide. 3. The imaging tube according to claim 1, wherein the planar electrode is a mesh electrode. 4. The imaging tube according to claim 1, wherein the tube axis of each channel of the modulator is inclined with respect to a line connecting the center of the entrance window and the electron gun. 5. The image pickup tube according to claim 1, wherein the scanning means is a deflection coil. 6. The image pickup tube according to claim 1, wherein the entrance window is a flat plate of calcium fluoride.