IMAGE INTENSIFIER TUBE AND ASSOCIATED NIGHT VISION DEVICE

Abstract

This image intensifier tube comprises the following elements fixed within an internal vacuum enclosure:– an input window (15) configured to receive and transmit photons;– a photocathode (16) capable of converting photons transmitted by the input window (15) into primary electrons, said photocathode (16) being fixed on an internal face of the input window (15);– an electron multiplier (18);– a support (30) configured to hold the electron multiplier (18) within the internal vacuum enclosure;– a phosphorescent screen (20); and– an optical output interface (21) configured to capture the photons emitted by the phosphorescent screen (20) to transmit them to the output of the image intensifier tube.The electron multiplier (18) is clamped in the support (30) by means of two damping rings, a first damping ring being arranged on a first face of the electron multiplier (18), and a second damping ring being arranged on a second face of the electron multiplier (18), said damping rings being made of a material having the following characteristics:– a Young's modulus less than or equal to 200 GPa;– a density greater than or equal to 7200 kg / m3;– a resistivity at 300K less than 1 Ω.m. Figure for the abstract: Fig 9.

Description

Title of the invention: IMAGE INTENSIFIER TUBE AND ASSOCIATED NIGHT VISION DEVICE Field of invention

[0001] The invention relates to the field of vision in a very dimly lit environment. Thus, the invention relates to a device conventionally called a “night vision device”.

[0002] The invention also relates to a specific element of a night vision device: the image intensifier tube, intended to allow, in a known manner, the luminosity of a scene to be amplified. More particularly, the invention aims to limit the acoustic noise generated by the image intensifier tube.

[0003] The invention finds application in many fields where it is sought to improve vision in dark environments, while ensuring stealth. In the military and defense field, the invention can be implemented for night surveillance, reconnaissance, navigation, piloting in low light conditions, or for specific applications such as night vision binoculars and night weapon sights. For hunting and outdoor activities, the invention helps in the detection of game in low light and in navigation during night expeditions. In scuba diving, the invention can be used to explore deep and dark ocean areas. In the fields of photography and cinematography, the invention can make it possible to capture images without the need for intense artificial lighting.

[0004] Furthermore, the invention can also be implemented in a large number of fields in order to limit noise pollution: in the aviation sector, for security and surveillance, in astronomy, in search and rescue operations, in the field of biology and ecology, the invention makes it possible to observe wildlife at night without disturbance due to artificial light, etc.

[0005] This invention therefore presents a multitude of potential applications. State of the art

[0006] As schematically illustrated in Figures 1 and 2 of the state of the art, a night vision device 110 is conventionally in the form of a pair of glasses intended to be placed in front of a sensor, the eye of a user, or both eyes when two devices are juxtaposed to form night vision binoculars.

[0007] This night vision device 110 integrates several elements placed on the optical axis al of the sensor or the user's eye in order to transform the image of the observed scene. More precisely, the scope comprises, from the exterior scene to the sensor or to the user's eye, an objective 12, an image intensifier tube 130 and an eyepiece 14.

[0008] The objective 12 conventionally comprises one or more lenses or a network of optical fibers making it possible to capture the photons of the electromagnetic radiation of the observed scene. The eyepiece 14, similarly to the objective 12, comprises one or more lenses or a network of optical fibers making it possible to capture and incidentally to visualize the photons of the light signal emitted by the image intensifier tube 130.

[0009] The image intensifier tube 130 comprises at least three distinct elements: a photocathode 16, an electron multiplier 18, and a phosphorescent screen 20.

[0010] The photocathode 16 is in the form of a semi-transparent photosensitive layer receiving the photons of the incident electromagnetic radiation, i.e. the photons transmitted by the objective 12. To do this, an entry window 15 transmits the photons from the objective 12 onto the photocathode 16 while ensuring the hermeticity of the external wall 23 of the image intensifier tube 130.

[0011] The photocathode 16 is generally produced in the form of a thin layer of metal or semiconductor applied to a layer of glass or material transparent to light. The material of the photocathode 16 is chosen according to its sensitivity to the image of the observed scene. The interaction of the photons of the incident electromagnetic radiation of the observed scene with the photocathode 16 produces, by photoelectric effect, an emission of electrons.

[0012] The emitted electrons, called primary electrons or photoelectrons, are then subjected to a first electric field within a first acceleration zone 17, making it possible to direct the primary electrons towards the electron multiplier 18. This first electric field is produced by applying a voltage between the photocathode 16 and the electron multiplier 18, typically a voltage of the order of 50 to 500 volts to guarantee a straight path for the electrons.

[0013] The electron multiplier 18, also called an electron amplifier, conventionally comprises a microchannel plate 25 covered by electrodes. This microchannel plate is also known by the acronym GMC or MCP for “microchannel plate” in the English literature. It is made from a plate of resistive or dielectric material with a thickness typically between 0.2 and 1 millimeter.

[0014] As illustrated more precisely in [Fig. 3] of the state of the art, the microchannels 25 pass right through the wafer of the electron multiplier 18 and are parallel to each other. They have a diameter of between 3 and 12 micrometers. Their internal wall is conventionally coated with a thin semiconducting layer produced by chemical treatment and allowing the transmission of an electric current. by hopping, known as "hopping-conduction" in the English literature. These microchannels 25 have an axis of revolution a2 inclined by an angle a3 of a few degrees, typically between 4 and 12 degrees, relative to the normal of the surface of the electron multiplier 18, so as to induce multiple collisions of the primary electrons 28 in the microchannels 25.

[0015] In addition to the first electric field created between the photocathode 16 and the electron multiplier 18, a second electric field is created between the two faces of the electron multiplier 18 by means of the electrodes placed on either side of the microchannel plate 25. This electric field makes it possible to charge the internal semiconductor layer of the microchannels 25 so that the multiple collisions of the primary electrons 28 in the microchannels 25 generate a large number of secondary electrons 29.This electric field also makes it possible, on the one hand, to accelerate the first secondary electrons 29 inside the microchannels 25, so that these first secondary electrons 29 collide again with the surface of the microchannels 25, in turn producing other secondary electrons 29, and so on, generating by this physical process a large number of secondary electrons 29; and on the other hand to accelerate the secondary electrons 29 by supplying energy, in order to orient them from the entrance of the microchannels 25 to the exit of the microchannels 25. Typically, the primary electrons 28 are multiplied by a factor of between 103 and 106 in the electron multiplier 18.

[0016] At the exit of the microchannels 25, these secondary electrons 29 are then moved linearly towards the phosphorescent screen 20, within a second acceleration zone 19, under the effect of a third electric field generated between the exit of the electron multiplier 18 and the phosphorescent screen 20, typically an electric field generated by a voltage of between 4 and 10 kV.

[0017] The phosphorescent screen 20 makes it possible to transform the secondary electrons 29 into light intensity. It is in the form of a phosphorescent layer or a layer of a luminophore material deposited on a substrate, conventionally made of glass. At the output of the phosphorescent screen 20, the image formed is transmitted to the eyepiece 14 by optical means, conventionally a network of optical fibers 21, possibly making it possible to return the image formed on the phosphorescent screen 20 to obtain a correct visualization of the observed scene.

[0018] To generate the three electric fields, electronic components 22 are conventionally arranged around an internal vacuum enclosure 24. The night vision system 110 thus formed therefore has optical elements, electronic components 22, and possibly a system for viewing the scene observed on the eyepiece 14. When the night vision system 110 is intended for the human eye, it is conventionally in the form of a telescope and the intensifier tube of images 130 is cylindrical.

[0019] In this embodiment, the photocathode 16, the electron multiplier 18, and the phosphorescent screen 20 typically have a diameter of between 15 and 30 millimeters.

[0020] In order to limit collisions between electrons and gas molecules, and in particular air, the two acceleration zones 17 and 19 are conventionally placed under vacuum, at a pressure in the ultra-high vacuum range, of the order of 107 to 10 10 bar. To do this, the photocathode 16, the electron multiplier 18, and the phosphorescent screen 20 are encapsulated in the internal vacuum enclosure 24.

[0021] The internal vacuum enclosure 24 is made up of several washers 50-52, conventionally made of ceramic 50 and metal 51-52, assembled together. To hold the electron multiplier 18, as illustrated in [Fig. 4], a support assembly 300 generally comprises an upper ring 51 and a lower ring 52 made of metal forming the internal vacuum enclosure 24 and making it possible to enclose the electron multiplier 18, while transmitting the electrical energy making it possible to power the electron multiplier 18. More precisely, the wafer of the electron multiplier 18 is gripped between the lower ring 52 and a metal elastic ring 530 pressed against the upper ring 51.

[0022] To form this support assembly 300, it is necessary to use materials capable of withstanding ultra-high vacuum conditions, conventionally measured by means of the “outgassing rate”. This outgassing rate represents the rate of release of the molecules absorbed by the materials when they are subjected to intense vacuum conditions. The materials usable in ultra-high vacuum typically have an outgassing rate of the order of 10 9mbar.s '.cm2. For example, polymer materials cannot be used to form this support assembly 300, since they have an outgassing rate making them unsuitable for withstanding ultra-high vacuum conditions.

[0023] Furthermore, modern night vision systems are also equipped with a brightness adaptation system, called "auto-gating" in the English literature, making it possible to limit saturation and increase brightness for the darkest scenes. This mechanism relies on the rapid detection of light variations to adjust, in a few nanoseconds, the generation of secondary electrons 29 and stabilize the brightness at the output of the image intensifier tube 130 typically between 10 and 12 candela / m2.

[0024] To do this, a first regulation method consists of modifying the multiplication gain of the electrons inside the electron multiplier 18, this modification being obtained by varying the voltage applied between the electrodes 26 of said multiplier.

[0025] If modifying the gain of the electron multiplier 18 is not sufficient to limit saturation, a second method consists of modulating the activation time of the photocathode 16.

[0026] This second method can be carried out by adjusting the electrical potential of the photocathode 16. Thus, when a significant variation in brightness is detected at the input or output of the image intensifier tube 130, the brightness adaptation system intervenes to modify, in a few nanoseconds, the voltage applied to the photocathode 16. This voltage modification makes it possible to temporarily deactivate the image intensification by reversing the direction of the first electric field generated between the photocathode 16 and the electron multiplier 18, thus preventing the primary electrons from being directed towards the electron multiplier 18. This brightness adaptation system can be triggered, for example, when a predetermined brightness threshold is exceeded, this threshold being for example a MOB threshold, acronym for the expression "Maximum of Brightness" in English literature.

[0027] This dynamic control of the amplification not only guarantees protection of the image intensifier tube 130 against the risks linked to excessive light intensity, but also offers a better view of the observed scene by adapting the resolution of the image to the surrounding conditions, without saturation or visual glare. As a result, operators benefit from clearer and more stable night vision, even in the face of sudden light variations, which is crucial for applications such as military or surveillance operations.

[0028] However, rapid variations in the voltage applied to the photocathode 16 cause sudden variations in the electrical potential between the photocathode 16 and the electron multiplier 18, and may also cause variations in the deflection of the wafer by piezoelectric effect, as illustrated in FIGS. 5b and 5c. This deflection or deformation of the wafer is a consequence of the electrostatic forces generated, this phenomenon having been experimentally observed, measured and demonstrated.

[0029] Indeed, in [Fig.5a], no electric potential is applied between the photocathode 16 and the electrode 26 of the electron multiplier 18. When an electric field is conventionally applied to direct the electrons onto the electron multiplier 18, for example by applying a voltage of -50 to 500 volts to the photocathode 16, a deflection, such as illustrated in [Fig.5b] may appear. When adapting to the brightness by temporarily deactivating the voltage applied to the photocathode 16, for example by applying a voltage of 5 to 10 volts to the photocathode 16, a deflection such as illustrated in [Fig.5c] may appear.

[0030] The variations of the deflection of the electron multiplier wafer 18, following the rapid change in direction of the voltage applied to the photocathode 16, can generate vibrations of the electron multiplier 18, which are then transmitted to the internal vacuum enclosure 24 of the image intensifier tube 130 by the support assembly 300. The vibrations of the internal vacuum enclosure 24 are then transmitted to the external cover 23, to the inlet window 15 and to the optical fiber network 21, and finally generate acoustic noise at the resonant frequency of the system.

[0031] This acoustic noise is particularly unpleasant for the user and dangerous in applications for which user discretion is an important, or even decisive, factor. A first solution for limiting this acoustic noise is to make electrical or electronic corrections, conventionally by signal processing means, to the brightness adaptation system. These electrical or electronic corrections are known by the English terms “anti-phase gating” and “spread-spectrum gating”.

[0032] Another conventional solution for limiting this acoustic noise is to increase the rigidity of the connection between the electron multiplier 18 and the internal vacuum enclosure 24, in order to prevent or reduce the vibration of the electron multiplier 18. This solution is mainly used for reasons of electrical or mechanical reliability, and only secondarily for acoustic reasons.

[0033] Thus, in document RU2649428, as illustrated in [Fig.6], a mechanical solution is proposed in order to attenuate the vibrations of the electron multiplier 18 during adaptation to the brightness by increasing the rigidity of the connection between the electron multiplier 18 and the internal vacuum enclosure 24. This mechanical solution is in the form of a support assembly 301 comprising a conductive ring 531 in contact with the upper ring 51 by means of a deformable beak mounted in compression between the upper ring 51 and the electron multiplier 18, the latter being mounted between the two rings by means of a metal spring.

[0034] Similarly, document US5994824 proposes a mechanical solution for attenuating the vibrations of the electron multiplier 18 during adaptation to brightness by enclosing the electron multiplier 18 with a support assembly 302 comprising two conductive rings 532 and 533, as illustrated in [Fig.7]. These conductive rings 532 and 533 also aim to prevent the vibration of the wafer of the electron multiplier 18, more precisely its axial or lateral displacement.

[0035] However, it appears experimentally that vibrations of the image intensifier tube 130 are still audible during adaptation to the brightness, even with these vibration attenuation systems.

[0036] Furthermore, the rings 531-533 used to enclose the electron multiplier 18 are also subject to a risk of displacement during shocks suffered by the in- image intensifier 130, resulting in a modification of the transmission of vibrations of the electron multiplier 18 and a modification of the sound waves generated during adaptation to the brightness. In addition, in the event of displacement, it is possible that the rings 531-533 do not ensure reliable electrical contact because these rings 531-533 also have the disadvantage of having a larger diameter than that of the electron multiplier 18 to contain a possible axial displacement of the latter. On the other hand, these conductive rings 531-533 can also mechanically place themselves in a hyperstatic mode, this state being able to cause rotation of the rings and a loss of contact with the electron multiplier 18, thus causing a loss of power to the electron multiplier 18 and the occurrence of electrical failures within the image intensifier.

[0037] It therefore appears necessary to reliably remedy the generation of sound waves by the image intensifier tubes 130 during adaptation to brightness. More particularly, it is necessary to provide a solution while taking into account the ultra-high vacuum medium in which the electron multiplier 18 is immersed, and ensuring that such a solution does not impact the path of the primary electrons and the secondary electrons generated, nor generally the level of detail of the scene to be observed, for example by shifting or damaging the electron multiplier 18. It is thus necessary to maintain the normal of the surface of the electron multiplier 18 in the optical axis and parallel to the axis of movement of the electrons. Furthermore, it is also essential to ensure a sufficient electrical supply to the electron multiplier for its proper operation. Presentation of the invention

[0038] The invention proposes to address this technical problem by placing two damping rings on either side of the electron multiplier wafer with particular properties to limit the transmission of vibrations, while guaranteeing the desired electrical transmission.

[0039] The invention arises from the observation that, contrary to the technical prejudice of those skilled in the art, the limitation of acoustic noise cannot be achieved by increasing the rigidity between the electron multiplier and the internal vacuum enclosure, the latter making it possible to prevent or reduce the vibration of the wafer.

[0040] Indeed, within the framework of the invention, tests were conducted by carrying out a brazing between the electron multiplier and the upper and lower rings for fixing the electron multiplier with the internal enclosure under vacuum. These tests showed that, even with the most rigid fixing possible, it is not possible to avoid the generation of acoustic noise.

[0041] Based on this observation, the inventors sought another method to limit the acoustic noise of image intensifier tubes during brightness adaptation.

[0042] Thus, instead of conventionally increasing the rigidity between the electron multiplier and the internal vacuum enclosure, the inventors sought to limit the transmission of vibrations from the electron multiplier, without seeking to limit the vibration phenomenon itself, while guaranteeing the desired electrical transmission. With this new approach, the inventors determined specific material parameters making it possible to meet all of these constraints.

[0043] Thus, according to a first aspect, the invention relates to an image intensifier tube comprising the following elements fixed within an internal vacuum enclosure: - an input window configured to receive and transmit photons; - a photocathode capable of converting photons transmitted by the input window into primary electrons, said photocathode being fixed on an internal face of the input window; - an electron multiplier comprising two parallel faces, capable of multiplying primary electrons into secondary electrons; - an electron multiplier support configured to hold the electron multiplier within the internal vacuum enclosure; - a phosphorescent screen transforming the secondary electrons into photons; and - an optical output interface configured to capture the photons emitted by the phosphorescent screen to transmit them to the output of the image intensifier tube.

[0044] The invention is characterized in that the electron multiplier is clamped in the support by means of two damping rings, a first damping ring being arranged on a first face of the electron multiplier, and a second damping ring being arranged on a second face of the electron multiplier, said damping rings being made of a material having the following characteristics: - a Young's modulus less than or equal to 200 GPa; - a density greater than or equal to 7200 kg / m3; and preferably a density greater than or equal to 8200 kg / m3; - a resistivity at 300K less than 1 Qm

[0045] These characteristics of the materials constituting the damping rings, preferably defined for temperatures of the order of 25°C, allow a damping capacity for the vibrations of the electron multiplier. On the other hand, the transmission of the sound pressure of the acoustic noise being proportional to the Young's modulus of the materials and inversely proportional to the density of the materials, these characteristics define materials having a certain ductility and elasticity while being of a relatively low density, thus making them particularly particularly suitable for damping the vibrations of the electron multiplier.

[0046] With this precise definition of the materials constituting the damping rings, the first damping ring and / or the second damping ring can be made of a material chosen from the group comprising gold, copper, lead, silver, platinum, tin or their alloys.

[0047] Furthermore, to withstand the ultra-high vacuum stresses in the image intensifier tube, the first damping ring and the second damping ring preferably have a degassing rate less than or equal to 107 mbar.s '.cm2. This characteristic also makes it possible to ensure that the materials constituting the damping rings do not emit particles under ultra-high vacuum conditions, these particles being able to damage the image intensifier tube and harm the integrity of the components of said tube.

[0048] According to one embodiment, the vibrations may also be limited by a coating material. In this embodiment, the tube also comprises an outer cover and a coating material disposed between an inner surface of the outer cover and an outer surface of the inner vacuum enclosure.

[0049] For example, to achieve effective vibration absorption, the coating material may be a polymer in the form of a silicone of the polydimethylsiloxane or PDMS type.

[0050] Preferably, to limit the transmission of vibrations between the internal vacuum enclosure and the inlet window, the coating material extends into a free space, for example between 1.5 and 2 millimeters, provided between the inlet window and a covering face of the external cover on said inlet window.

[0051] Preferably, to limit the transmission of vibrations between the internal vacuum enclosure and the output interface via a power supply unit of the tube, the coating material extends into a free space, for example between 0.8 and 1.2 millimeters, provided between the electrical power supply unit and a covering face of the external cover on said electrical power supply unit.

[0052] Preferably, to limit the transmission of vibrations between the internal vacuum enclosure and the output interface via the power supply unit, the coating material also extends into a free space, for example between 0.5 and 1.2 millimeters, provided between said electrical power supply unit and said external cover.

[0053] Preferably, to limit the transmission of vibrations between the internal vacuum enclosure and the output interface via the power supply unit, the coating material also extends into a free space, for example between 0.8 and 1.2 millimeters, provided between the electrical power supply unit and the internal vacuum enclosure.

[0054] Preferably, to limit the transmission of vibrations between the internal vacuum enclosure and the inlet window or the outlet interface, the coating material also extends into a free space, for example between 2 and 3 millimeters, provided between said internal vacuum enclosure and the external cover.

[0055] According to a second aspect, the invention also relates to a night vision system comprising: an objective; an image intensifier tube according to the first aspect of the invention; and an eyepiece and / or a sensor. Brief description of the figures

[0056] The invention will be better understood on reading the following description, given solely by way of example, and carried out in relation to the appended drawings, in which identical references designate identical or similar elements, and in which:

[0057] [Fig.l] illustrates a schematic sectional view of a state-of-the-art night vision device;

[0058] [Fig.2] illustrates a perspective view of the night vision device of [Fig.l];

[0059] [Fig.3] illustrates a schematic sectional view of the electron multiplier of the night vision device of [Fig.l];

[0060] [Fig.4] illustrates a schematic sectional view of the electron multiplier mounting bracket on an enclosure of the night vision device of [Fig.l];

[0061] [Fig.5a][Fig.5b][Fig.5c] illustrate three schematic sectional views of the deflections of the electron multiplier of the night vision device of [Fig.l] during adaptation to brightness;

[0062] [Fig.6] illustrates a schematic sectional view of a support for fixing an electron multiplier in an enclosure of a night vision device according to another embodiment of the state of the art;

[0063] [Fig.7] illustrates a schematic sectional view of a support for fixing an electron multiplier in an enclosure of a night vision device according to another embodiment of the state of the art;

[0064] [Fig.8] illustrates a schematic sectional view of a support for fixing an electron multiplier in an enclosure of a night vision device according to an embodiment of the invention;

[0065] [Fig.9] illustrates a schematic sectional view of a night vision device according to one embodiment of the invention; and

[0066] [Fig. 10] illustrates a partial sectional schematic view of the night vision device of [Fig. 9]. Detailed description of the invention

[0067] [Fig. 9] illustrates a night vision device 11 incorporating an image intensifier tube 13 according to the invention. As illustrated in [Fig. 1] of the prior art, the night vision device 11 is in the form of a goggle intended to be placed in front of a sensor, the eye of a user, or both eyes when two devices are juxtaposed to form night vision binoculars. This night vision device 11 incorporates several elements placed on the optical axis a1 of the sensor or the user's eye in order to transform the image of the observed scene. More precisely, the goggle comprises, from the scene external to the sensor or the user's eye, an objective 12, the image intensifier tube 13 of the invention and an eyepiece 14.

[0068] As described above, the objective 12 comprises one or more lenses or an optical fiber network for capturing the photons of the electromagnetic radiation of the observed scene. The eyepiece 14, similarly to the objective 12, comprises one or more lenses or an optical fiber network for capturing and incidentally viewing the photons of the light signal emitted by the image intensifier tube 13.

[0069] The image intensifier tube 13 comprises at least three distinct elements integrated in an internal vacuum enclosure 24: a photocathode 16, an electron multiplier 18, and a phosphorescent screen 20.

[0070] As described previously, the photocathode 16 is in the form of a semi-transparent photosensitive layer receiving the photons of the incident electromagnetic radiation, i.e. the photons transmitted by the objective 12. To do this, an input window 15 transmits the photons from the objective 12 onto the photocathode 16 while guaranteeing the hermeticity of an external wall 23 of the image intensifier tube 13.

[0071] The photocathode 16 is generally produced in the form of a thin layer of metal or semiconductor applied to a layer of glass or material transparent to light. The material of the photocathode 16 is chosen according to its sensitivity to the image of the observed scene. The interaction of the photons of the incident electromagnetic radiation of the observed scene with the photocathode 16 produces, by photoelectric effect, an emission of electrons.

[0072] The emitted electrons, called primary electrons, are then subjected to a first electric field within a first acceleration zone 17 making it possible to direct the primary electrons towards the electron multiplier 18. This first electric field is produced by applying a voltage between the photocathode 16 and the electron multiplier 18, typically a voltage of between 50 and 500 volts to guarantee a straight path for the electrons.

[0073] In addition to the first electric field created between the photocathode 16 and the multiplier of electrons 18, a second electric field is created between the two faces of the electron multiplier 18 by means of the electrodes placed on either side of the microchannel plate 25. This electric field makes it possible to charge the internal semiconductor layer of the microchannels 25 so that the multiple collisions of the primary electrons 28 in the microchannels 25 generate a large number of secondary electrons 29. This electric field also makes it possible, on the one hand, to accelerate the first secondary electrons 29 inside the microchannels 25, so that these first secondary electrons 29 collide again with the surface of the microchannels 25 producing in turn other secondary electrons 29, and so on generating by this physical process a large number of secondary electrons 29; and on the other hand to accelerate the secondary electrons 29 by supplying energy, in order to orient them from the entrance of the microchannels 25 to the exit of the microchannels 25.Typically, the primary electrons 28 are multiplied by a factor of between 103 and 106 in the electron multiplier 18. At the exit of the microchannels 25, these secondary electrons 29 are then moved linearly towards the phosphorescent screen 20, within a second acceleration zone 19, under the effect of a third electric field generated between the electron multiplier 18 and the phosphorescent screen 20, typically an electric field generated by a voltage of between 4 and 10 kV.

[0074] The phosphorescent screen 20 makes it possible to transform the secondary electrons 29 into light intensity. It is in the form of a phosphorescent layer or a layer of a luminophore material deposited on a substrate, conventionally made of glass.

[0075] At the output of the phosphorescent screen 20, the image formed is transmitted to the eyepiece 14 by optical means, conventionally a network of optical fibers 21 possibly making it possible to return the image formed on the phosphorescent screen 20 to obtain a correct visualization of the observed scene.

[0076] To generate the three electric fields, electronic components 22 are conventionally arranged around the internal vacuum enclosure 24. The night vision system 11 thus formed therefore has optical elements, electronic components 22, and possibly a system for viewing the scene observed on the eyepiece 14. When the night vision system 11 is intended for the human eye, it is conventionally in the form of a telescope and the image intensifier tube 13 is cylindrical.

[0077] In the embodiment of [Fig.9], the photocathode 16, the electron multiplier 18, and the phosphorescent screen 20 conventionally have a diameter of between 15 and 30 millimeters.

[0078] In order to limit collisions between electrons and gas molecules, and in particular air, the two acceleration zones 17 and 19 are conventionally placed under vacuum, at a pressure in the ultra-high vacuum range, of the order of 107 to 10 10 bar. To do this, the photocathode 16, the electron multiplier 18, and the phosphorescent screen 20 are encapsulated in the internal vacuum enclosure 24.

[0079] The internal vacuum enclosure 24 is made up of several washers 50-52, conventionally made of ceramic 50 and metal 51-52, assembled together.

[0080] To hold the electron multiplier 18, as illustrated in [Fig.8], a support assembly 30 comprises an upper ring 51 and a lower ring 52 made of metal forming the internal vacuum enclosure 24 and making it possible to enclose the electron multiplier 18 while transmitting the electrical energy making it possible to power the electron multiplier 18.

[0081] According to the invention, the electron multiplier wafer 18 is clamped, by means of two damping rings 54-55, between the lower ring 52 and a metallic elastic ring 53 pressed against the upper ring 51.

[0082] More specifically, as illustrated in [Fig.8], a first damping ring 54 is disposed on a first face 38 of the electron multiplier 18, and a second damping ring 55 is disposed on a second face 39 of the electron multiplier.

[0083] According to the invention, to guarantee the electrical conductivity and the damping of the vibrations of the electron multiplier 18 during the brightness adaptation phase, the damping rings 54-55 are made of a material having the following characteristics: - a Young's modulus less than or equal to 200 GPa; - a density greater than or equal to 7200 kg / m3; and preferably a density greater than or equal to 8200 kg / m3; - a resistivity at 300K less than 1 Qm

[0084] Advantageously, this material also has a degassing rate less than or equal to 107 mbar.s '.cm 2.

[0085] Young's modulus can be conventionally measured by fixing one end of the ring and applying a progressive force to another end of the ring. Density and resistivity are intrinsic and known characteristics of materials.

[0086] With these specific constraints, the first damping ring 54 and / or the second damping ring 55 can thus be made of a material chosen from the group comprising gold, copper, lead, silver, platinum or their alloys. These first and second damping rings 54 and 55 are arranged respectively on the electrodes arranged on the faces 38 and 39 of the electron multiplier 18.

[0087] According to an exemplary embodiment, the first damping ring 54 and / or the second damping ring 55 may be in the form of a copper ring with a thickness of 45 micrometers or in the form of a gold ring with a thickness of 2 micrometers. Conventionally, these rings are deposited on the faces of the electron multiplier 18 by a chemical and / or physical deposition process. The first damping ring 54 and the second damping ring 55 thus form intermediate contact elements between the electron multiplier 18 and, respectively, the metal elastic ring 53 and the lower ring 52.

[0088] Conventionally, the electron multiplier 18, equipped with its two damping rings 54 and 55, is arranged within the support 30, and more particularly between the upper ring 51, the elastic metal ring 53 and the lower ring 52. The electron multiplier 18 can be held in place by means of a metal spring.

[0089] With reference to figures 9 and 10, at least one electrical power supply unit 22 is arranged between the internal vacuum enclosure 24 and the external cover 23 in order to supply electricity to the acceleration zones 17 and 19, and the electron multiplier 18.

[0090] A coating material 43 may also be used to fill the empty space. This coating material extends between the external surface of the vacuum enclosure 24 and the external cover 23. More particularly, as illustrated in [Fig. 10], the coating material 43 extends in at least one of the following areas: - in a free space 44, between 1.5 and 2 millimeters, provided between the inlet window 15 and a covering face 45 of the external cover 23 on the inlet window 15; - in a free space 46, between 0.8 and 1.2 millimeters, provided between the power supply unit 22 and a covering face 47 of the external cover 23 on the power supply unit 22; - in a free space 48, between 0.5 and 1.2 millimeters, provided between the power supply unit 22 and the external cover 23; - in a free space 49, between 0.8 and 1.2 millimeters, provided between the power supply unit 22 and the internal vacuum enclosure 24; and - in a free space 60, between 2 and 3 millimeters, provided between the internal vacuum enclosure 24 and the external cover 23.

[0091] The coating material 43 is preferably made of polydimethylsiloxane or PDMS, this material having the advantage of being an excellent electrical insulator while having a Young's modulus suitable for damping any vibrations transmitted by the internal vacuum enclosure 24. However, other materials having similar properties can obviously be envisaged without departing from the scope of the present invention.

[0092] With the damping rings 54-55, and possibly the coating material 43 , the invention makes it possible to limit the transmission of vibrations of the electron multiplier 18 during adaptation to the brightness by temporarily deactivating the voltage applied to the photocathode 16. Thus, the image intensifier tube 13 and, more generally, the night vision device 11 make less noise, promoting the stealth of the user.

Claims

Claims

1. An image intensifier tube (13) comprising the following elements fixed within an internal vacuum enclosure (24): - an input window (15) configured to receive and transmit photons; - a photocathode (16) capable of converting photons transmitted by the input window (15) into primary electrons (28), said photocathode (16) being fixed on an internal face of the input window (15); - an electron multiplier (18) comprising two parallel faces (38, 39), capable of multiplying the primary electrons (28) into secondary electrons (29); - a support (30) of the electron multiplier (18) configured to maintain the electron multiplier (18) within the internal vacuum enclosure (24); - a phosphorescent screen (20) transforming the secondary electrons (29) into photons;and - an optical output interface (21) configured to capture the photons emitted by the phosphorescent screen (20) to transmit them to the output of the image intensifier tube (13); characterized in that the electron multiplier (18) is clamped in the support (30) by means of two damping rings (54, 55), a first damping ring (54) being arranged on a first face (38) of the electron multiplier (18), and a second damping ring (55) being arranged on a second face (39) of the electron multiplier (18), said damping rings (54, 55) being made of a material having the following characteristics: - a Young's modulus less than or equal to 200 GPa; - a density greater than or equal to 7200 kg / m3; - a resistivity at 300K less than 1 Qm;

2. An image intensifier tube according to claim 1, further comprising an outer cover (23) and a potting material (43) disposed between an inner surface of the outer cover (23) and an outer surface of said inner vacuum enclosure (24).

3. An image intensifier tube according to claim 2, wherein the coating material (43) extends into a free space (44), for example between 1.5 and 2 millimeters, provided between said inlet window (15) and a covering face (45) of the external cover (23) on said entrance window (15).

4. An image intensifier tube according to claim 2 or 3, further comprising a power supply unit (22), the coating material (43) extending into a free space (46), between 0.8 and 1.2 millimeters, provided between said power supply unit (22) and a covering face (47) of the outer cover (23) on said power supply unit (22).

5. Image intensifier tube according to one of claims 2 to 4, also comprising a power supply unit (22), the coating material (43) extending into a free space (48), between 0.5 and 1.2 millimeters, provided between said power supply unit (22) and said external cover (23).

6. Image intensifier tube according to one of claims 2 to 5, also comprising a power supply unit (22), the coating material (43) extending into a free space (49), between 0.8 and 1.2 millimeters, provided between said power supply unit (22) and said internal vacuum enclosure (24).

7. Image intensifier tube according to one of claims 2 to 6, in which the coating material extends into a free space (60), between 2 and 3 millimeters, provided between said internal vacuum enclosure (24) and said external cover (23).

8. Image intensifier tube according to one of claims 2 to 7, in which the coating material (43) is a polymer in the form of a silicone of the polydimethylsiloxane or PDMS type.

9. Image intensifier tube according to one of claims 1 to 8, wherein the first damping ring (54) and / or the second damping ring (55) are made of a material selected from the group comprising gold, copper, lead, silver, platinum or their alloys.

10. Image intensifier tube according to one of claims 1 to 9, in which the first damping ring (54) and the second damping ring (55) have a degassing rate less than or equal to 107 mbar.s '.cm 2.

11. Night vision system (11) comprising: - a lens (12); - an image intensifier tube (13) according to one of the preceding claims; and - an eyepiece (14) and / or a sensor.

Images