FR2570876A1 - IMAGE AMPLIFIER TUBE, MANUFACTURING METHOD THEREOF, AND COATING FOR FRONT PLATE OF SUCH A TUBE - Google Patents

Abstract

IMAGE AMPLIFIER TUBE INCLUDING A FRONT PLATE 12 MADE OF OPTICAL MATERIAL AND INCLUDING LIGHT RECEPTION AND TRANSMISSION SURFACES, PHOTO-EMITTING MEANS 19 PROVIDED ON THE SAID TRANSMISSION SURFACE ALLOWING THE EMISSION OF ELECTRONS TO REPLY THE LIGHT TO THE LIGHT RECEIVED BY THE SAID PHOTO-EMITTING MEANS FROM THE SAID LIGHT TRANSMISSION SURFACE, A MICRO-CHANNEL PLATE 25 ADJACENT TO THE SAID PHOTO-EMITTING MEDIA AND ALLOWING TO AMPLIFY THE ELECTRONS EMITTED BY THE SAID PHOTO-EMITTING MEDIA, A 21 EXTENDING ALONG A PART OF THE SAID FRONT PLATE AND JOINING THE SAID PHOTO-EMITTING MEANS, THE SAID FIRST COATING CONSISTING OF LIGHT-ABSORBING MATERIAL AT LEAST IN THE NEAR AND NON-REFLECTING INFRARED REGION, AND A SECOND OF LIGHT-ABSORBING MATERIAL FIRST COATING AND JOINING THE SAID PHOTO-EMITTING MEANS, THE SAID SECOND COATING CONSISTING OF CONDUCTIVE METAL MATERIAL UR OF ELECTRICITY.

Description

The present invention relates to amplifier tubes

  image of the type used in night vision systems and, no-

  a picture amplifier tube with halo reduction

  parasite and a method of manufacturing said tube.

  Image intensifier tubes multiply the light

  cidente they receive and therefore increase the flow

  which can be delivered to a camera or directly to the eye of an observer. These devices are particularly useful for

  provide images of dark areas and have applications both

  industrial than military. They are for example used to improve

  improve night vision of aviators, to photograph bodies

  extra-terrestrial and to allow people with retina-

  you pigmentary (night blindness) to see at night.

  Modern image amplifier tubes have a microchannel plate which is a thin glass plate crossed by a network of microscopic holes. Each hole is designed to act as a channel-emitting secondary emission electron multiplier. When the microchannel plate is placed in the plane of an electronic image in an amplifier tube, it makes it possible to

  achieve a gain of ten to twenty thousand as well as a very high resolution

  lution. Insofar as each of the microchannel plate channels

  nales works almost independently of all the others, a bright point light source saturates a few channels but does not

  not extend to adjacent areas. This characteristic of "satu-

  local ration "makes these tubes less sensitive to the phenomenon

  spreading bright areas. However, these tubes pre-

  feel a drawback known as "parasitic halo". The stray halo appears when a diffuse light arrives at the light entry or on the focal plane of the tube. In the image amplifier, this translates into a loss of contrast by lightening

  dark parts of the image, which reduces the visibility of objects

  small or low contrast jets. In extreme cases

  mes, it can even cause complete loss of information

  much of the visual field.

  The parasitic halo is essentially due to the light outside the axis which is reflected towards the interior of the tube and which is amplified to appear in the visual field in the form of parasitic images. Sources of parasitic halo include rays of bright light that enter the normal field of view at angles outside the axis. Light rays coming from sources outside the normal visual field are reflected at the interface of the front plate and the conductive metallic layer towards the photoemitting material of the tube, which causes an emission.

  from the latter to the image focused on the photoemeter material-

tor and generates the parasitic halo.

  Various attempts have been made to delete or re-

  mute the stray halo by adding material to the tube, which absorbs light off the axis and prevents it from being reflected back

  the light emitting layer. For example, black rings have been made

  read on the surface reflecting the light outside the axis. These rings were held in place by sealing a glass ring on the surface or by melting a glass ring on the surface to sandwich the ring between the reflecting surface and the ring.

  glass. This operation proved difficult to perform and very costly.

  teuse. Another technique consisted in making a groove by gra-

  between the light entry surface and the reflected surface

  and fill this groove with absorbent material

  light. Here again, this operation proved difficult to carry out.

  ser and is also very expensive.

  The object of the present invention is therefore to provide a tube

  bright image amplifier with a parasitic halo

  duit and can be manufactured at lower cost. The present invention also aims to provide a method for manufacturing

  a tube of this type very economically and efficiently.

  This image amplifier tube has a front plate

  made of optical material and intended to transmit light, and photoemitting means intended to emit electrons in response to the transmitted light. During the manufacture of the tube, a phase is provided during which a first layer of a material is formed which substantially reduces the reflection and / or is capable

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  absorb light especially in the near infrared region, on

  the front plate adjacent to any surface from which the

  matter outside the axis could be reflected towards the photo-

  emitter, and a subsequent phase during which a second layer of an electrically conductive metallic material is deposited on the pre

down again.

  The tube thus obtained comprises a front plate designed to receive and transmit the incoming light, a photoemitting means

  to emit the electrons, and a microchannel plate per-

  putting to amplify the emitted electrons. The front plate also has

  a surface where light outside the incoming axis can

  be reflected towards the light emitting means and the region not reflected

  is adjacent to said surface.

  The various objects and characteristics of the invention are-

  will now be detailed in the description which follows, made to

  by way of nonlimiting example, with reference to the appended figures which represent:

  - Figure 1, a perspective view of an amplificate tube-

  ur image, - Figure 2, a cross-sectional view of a glass front plate used in the image amplifier tube according to the present invention, - Figure 3, a partial cross-sectional view of a

  Typical amplifier tube according to the present invention.

  FIG. 1 represents a simplified perspective view of an image amplifier tube 10. The image amplifier tube

  comprises a cylindrical housing 11 in which is housed a plate

  that front 12 made of optical material and designed to re-

  to receive and transmit light. The front plate 12 is normally

  sealed inside the housing 11 and is surrounded by a perimeter flange

  spherical 15. The light rays coming from the visual field (noted

  "in the axis" in Figure 1) cross the front plate 12 and are di-

  rigged to the image amplifier where their amplitude is increased.

  In many known arrangements of this type, the light which pro-

  comes from outside the visual field (noted "outside the axis" in Figure 1) is reflected on an inner surface of the tube 10 and is

  returned to the amplifier o its amplitude is also increased.

  This light outside the axis is the source of the parasitic halo

as will be seen below.

  In Figure 3, we see that the image amplifier tube consists of three main elements: the front plate 12 which operates like a cathode, a front plate (placed inside the chamber 18 and not represented in the figure) which functions in the manner of an anode, and a microchannel plate 25 housed between these elements and placed at a distance from the front plate 12 and from the chamber 18. The front cathode and anode plates are of

  preferably made of glass with high optical qualities

  vee. The microchannel plate 25 is also made of glass pos-

  attractive secondary emission property and conductive characteristics. The microchannel plate 25 is mounted in the image tube 10, its inlet and outlet faces being parallel to the cathode front plate 12 of the image tube and a phosphor screen being associated with the anode front plate . The microchannel plate 25

  works in known manner to amplify the photoelectrons pro-

  supplied by the incoming light in order to increase the light output of the tubes. The front plate 12 can be made of high quality clear optical glass such as Corning 7056. This glass consists of 70% silica (SiO2), 17% boric oxide (B203), 8% potassium hydroxide (K20 ), 3% alumina (A1203) and 1% soda respectively

  (Na20) and lithium oxide (Li20). Other glasses may well

stretched also be used.

  With reference to FIG. 2, the front plate 12 comprises a central body part of generally circular shape 12a and

  a flange portion of lesser thickness 12b in the form of a flange

  turning the body part. A surface 13 of the front plate 12

  extends continuously through the body parts and re-

  edge respectively 12a and 12b and the part of this surface extends

  dant on the rim part 12b, and a small adjacent portion of the central body part 12a fits under the flange 15 and is there

  fixed to retain the front plate in the housing 11. The part

  aunt of surface 13, i.e. the part surrounded by the flange

  , is the exposed surface of the front plate 12 on which the

incoming mother comes to strike.

  The front plate 12 also comprises surface parts 16a and 16b which are generally parallel to the surface 13 and which extend respectively over the body part 12a and the rim part 12b. Due to the difference in thickness between the body part 12a and the rim part 12b, the surface parts 16a and 16b are located in different planes, the part 16a being further from the surface 13 than the part 16b. Between the surface portions 16a and 16b extends a connecting surface portion 16c which, in the embodiment shown here, generally has the

shape of a cone trunk.

  According to a known conventional arrangement, the surface part 16a is covered with a light-emitting wafer 19 designed so that the light which strikes the exposed surface part 13 and finally

  section 19 causes the emission of electrons. These electrons are ac-

  celerated through an interval by an electric field towards the microchannel plate 25, which causes the secondary emission of electrons

  in accordance with known principles. The 19 light emitting unit

  tuelle is a suitable device for gallium arsenide (GaAs), but other suitable materials can be used. In known devices, a metallic coating is applied to surfaces 16b, 16c and part of 16a to establish a connection

  between the unit 19 and the external current source.

  The conductive metallic coatings used until now are satisfactory in several respects, but are often the source of the parasitic halo. The light outside the axis which

  strikes the exposed part of the surface 13 strikes this metallic coating

  metallic and is reflected in the central body part 12a where it

  hits the light emitting unit 19 and causes the emission of electro

  sections which are accelerated towards the microchannel plate 25, causing

  thus a secondary emission of electrons. Insofar as the plac-

  that at microchannels 25 causes an increase in the light flow,

  it actually increases the unwanted halo.

  In this case, the reduction of the parasitic halo is ensured

  by means of a coating of material 21 which is applied to the sur-

  faces 16b and 16c and also on a surface part 16a adjacent to the wafer 19. This coating is made of non-reflective material.

  bending capable of absorbing light, especially in the re-

  near infrared region. Materials with these characteristics are metallic oxides. However, in many cases, this coating is not electrically conductive. A second coating 22 of electrically conductive metallic material is therefore applied to the coating 21, so that this coating 22 makes contact with the wafer 19 and thus establishes an electrical connection between the wafer 19 and an external bias power supply.

  (not shown). In an advantageous embodiment, the coating

  tion 21 consists of chromium oxide and the coating 22 of elemental chromium. Coatings 21 and 22 can be applied in any suitable manner. An advantageous method of application

  coatings 21 and 22 is provided by the known method of spraying

  station in which a metal material electrode is bombarded

  of positive gas ions and the pulverized particles of mixed material

  resulting metal are deposited on a surface located in

  the area adjacent to the sprayed particles.

  The present invention has adapted the spraying technique for depositing the coating 21 of chromium oxide and the coating 22 of chromium on the surfaces 16b, 16c and on a surface portion 16a which

  is placed in the extension of 16c. In the spraying process

  tion applied here, the surface 13 of the glass front plate is placed

  created on a support in a room. To deposit the coating 21, the chamber is evacuated to obtain a relatively low pressure and a volume of oxygen mixed with an inert gas, for example argon, is

  introduced into the room. Any arrangement of spray electrodes

  tion of plasma induced by radio frequency can be used. At least one of these electrodes, referred to as the target electrode, is

  placed in the room. The target electrode is made in the material

  elementary line which must be sprayed. In the embodiment

  preferred, the target electrode material is chromium. A radio-

  frequency of about 13.56 MHz is applied to argon and oxygen.

  Ionized atoms of argon and oxygen are thus obtained, the de-

  placement is accelerated by the presence of a potential difference

  in the bedroom. Ionized argon ions bombard the electrode below

  ble and the chromium atoms leave the electrode by sputtering.

  The energy communicated to argon during ionization is transferred to the chromium atoms. Due to the presence of oxygen, chromium reacts with oxygen to form chromium oxide which is then deposited on the front plate. The wafer 19 which has already been applied to the surface 16a is protected during the deposition and therefore does not receive

not the coating 21.

  When the coating 21 has been deposited, the oxygen present in the chamber is evacuated and the argon is maintained at the level necessary for the spraying operation. The operation is then repeated and gives

  place a deposit of the second coating 22 composed of the metal oxide-

  lique in its elementary form which, in the present embodiment

  tion, is chromium. This layer is deposited at a thickness of approximately 2000 A. During the deposition of the second coating 22, the wafer 19 is again protected so that it does not receive the coating 22

  on most of its surface, but not on its extreme parts

  mes o continuity with section 19 must be ensured.

  It is also possible to gradually reduce the

  oxygen centering after depositing a sufficient thickness of

  duction 21 and continue spraying until

  that the material deposited is only elemental chromium. We ob-

  thus holds a transition layer and the spraying operation

  can take place without interruption.

  The chromium oxide coating 21 thus obtained takes the place of

  anti-reflective layer capable of absorbing light in the infrared

  near red, so that the light outside the axis coming from the surface 13 receiving the light is not reflected towards the microchannel plate 25. The coating 22 of elementary chromium thus obtained

  provides the electrical connection between unit 19 and the power supply

  external electrical supply. Coating 21 has a dark, non-reflective appearance while coating 22 has a shiny and

  silver found in standard metallic coatings.

  The resistance between the light emitting wafer 19 and the conductive coating 22 is low and is substantially the same as that obtained with a conventional conductive layer. This is the oxygen content of

  the coating of chromium oxide 21 which determines the reflective properties

  and absorbing in the near infrared at the interface of the coating 21 and the glass front plate 12, and this is the absence

  of oxygen in the metal coating 22 which ensures good conduc-

electrical activity.

  Of course, it is also possible to use

  rates other than chromium for coating 21, subject

  that these metals give rise to oxides with the properties

  desired optical tees and having an acceptable electrical conductivity

  table. In addition, the material of the coating 21 may, at least in principle, be different from the material of the coating 22 and not be associated with it, if this is desired or desirable. The materials

  coating can be chosen individually for their properties

  optical and electrical tees required and for their ability to adhere

to the material of the neighboring layer.

  The image amplifier tube 10 is shown in detail in FIG. 3. It can be seen that the flange 15 is an integral part of the cylindrical body 11 and that the front plate 12 is located under the flange 15 and supported at its ends by two elements in made of

  L, one of which is noted 30. The central body part 12a measures approx.

  ron 5.5 mm while the rim 12b measures approximately 3.8 mm.

  Under the front plate 12 is the microchannel plate 25. The two plates 12 and 25 are sealed to the body of the tube 17 by means of conventional fasteners. Room 18 contains the

  anode fiber optic front plate and other components

  image amplifier tube tutorials. From top to bottom, the complete tube measures approximately 2.5 to 3.5 cm in length with a typical diameter

  3.5 cm and we can therefore say that the complete unit is very small.

  The above description relates to an embodiment

  advantageous of the invention, but it is understood that various chan-

  modifications and modifications can be made without deviating from

  the true spirit or scope of the invention.

Claims (10)

  1. Image amplifier tube comprising a front plate (12) made of optical material and comprising light reception and transmission surfaces, photoemitting means (19) provided on said transmission surface making it possible to emit electrons response to the light received by said photoemitting means in   from said light transmitting surface, a plate   as microchannels (25) adjacent to said photoemitting means and per-   putting to amplify the electrons emitted by said photoemeter means-   teurs, a first coating (21) extending along a part of   said front plate and joining said photoemitting means, la-   said first coating consisting of material absorbing light   at least in the near infrared region and not reflected   health, and a second coating (22) deposited on said first coating and joining said photoemitting means, said second coating   being made of metallic material conducting electricity.   2. Image amplifier tube according to claim 1, characterized in that the material of said first coating is a metal oxide.   3. Image amplifier tube according to claim 2,   characterized in that said metal oxide material is oxy-   of chromium, and in that said material of said second coating is chromium.   4. Method of manufacturing an image amplifier tube   comprising a front plate made of optical material making it possible to receive   see and transmit light and associated photoemitting means   ciés to the front plate allowing to emit electrons in response to the light transmitted through the front plate, including the   deposition phases of a first coating of non-reflective material   healthy and absorbing light in the near infrared on a part   of the light transmitting surface and on the photo-   adjacent transmitters, and depositing a second coating of a material   metallic line of electricity on the first coating and rejoin- hampering the photoemitting means.   5. Method according to claim 4, characterized in that   that said spraying process involves bombarding a ma-   metallic material by argon ions.   6. Method according to claim 5, characterized in that   that said spraying process provides for the implementation of a ma- chrome metal material.   7. Coating intended for a front plate of an amplified tube   image creator, the front plate comprising a surface receiving the light, a surface transmitting the light opposite to the first and   lateral surfaces connecting the receiving and trans-   light mission, comprising a first part made of non-reflecting material absorbing near infrared carried out on a large   part of the side surfaces so that the light received below   off the axis through said light receiving surface cannot   not pass through the light-transmitting surface, and a se-   this part made of electrically conductive metallic material placed on the said first part.   8. Coating according to claim 7, characterized in   that said material of said first part is a metal oxide   than. 9. Coating according to claim 7, characterized in   that said metal oxide is chromium oxide.   10. Coating according to claim 7, characterized in   that said material of said second part is chromium.