Electromagnetic radiation detection device

Abstract

The invention relates to an electromagnetic radiation detection device (100) comprising: - a housing comprising a first hermetically sealed and juxtaposed enclosure (102) and a second enclosure (104), - a sensor (120) arranged in the first enclosure and formed by a flat surface sensitive to said electromagnetic radiation, said sensor having an optical axis (X) centered with respect to said sensor, wherein: - the first enclosure (102) comprises a window (115) transparent to electromagnetic radiation arranged opposite said sensor, and the second enclosure (104) comprises a first window (111) receiving electromagnetic radiation from outside the housing and a second window (113) transparent to electromagnetic radiation and adjacent to the window (115) of the first enclosure, - the second enclosure (104) comprises a cold element (128). Figure to be published with the abstract: [Fig. 1]

Description

Title of the invention: Electromagnetic radiation detection device Technical field of the invention

[0001] The invention relates to devices for detecting electromagnetic radiation (such as infrared), intended in particular to equip self-guided projectile homing devices (missiles, rockets, etc.) or thermal cameras, binoculars and night vision goggles, telescopes, and more generally any observation device based on the principle of detecting electromagnetic radiation, for example using a so-called cooled sensor. State of the prior art

[0002] Electromagnetic radiation detection devices are generally equipped with an electromagnetic radiation sensor (commonly referred to as "FPA", an acronym for "Focal Plane Array") which can only operate in a vacuum and at low temperature.

[0003] The sensor, placed in a housing defining a vacuum enclosure and provided with a window transparent to electromagnetic radiation for the transmission of the latter to the sensor, is generally mounted on an end wall of a cold finger in which is housed a heat exchanger ensuring the cryogenic cooling of the sensor, to a temperature below 200 K, in particular below 150 K, in particular below 100 K.

[0004] Most sensors used to date have a surface consisting of a matrix of pixels sensitive to electromagnetic radiation, which can perceive it in the flat cone defined by the surface of the sensor, i.e. at 2ir steradians. It is necessary to limit the cone of perception so that it does not include external sources of electromagnetic radiation (so-called out-of-field), constituting parasitic radiation.

[0005] This is why a screen equipped with a diaphragm is generally interposed between the sensor and the window: this screen is supposed to act as a barrier to parasitic electromagnetic radiation.

[0006] However, the interposition of a screen is not sufficient to prevent stray radiation from reaching the sensor, for at least two reasons. On the one hand, the screen itself can be a source of electromagnetic radiation. To limit this radiation, it is customary to cool the screen by using the aforementioned cryogenic source. For this purpose, the screen is generally painted matte black and mounted on the cold finger, the screen thus being kept in operation at a temperature temperature below room temperature. On the other hand, it is common for electromagnetic radiation from an off-field source, although not directly reaching the sensor, to reach it by reflection on the wall of the screen, inside it.

[0007] Many solutions have been proposed to remedy this problem, for example the shape of the screen can be optimized to reduce the number of incident off-field rays that can reach the sensor, and / or the screen can include a superposition of baffles that trap incident rays from off-field sources.

[0008] While such solutions do indeed make it possible to reduce the impact of parasitic radiation on the performance of the sensor, they nevertheless have the double disadvantage of complexity and manufacturing cost.

[0009] The invention aims in particular to remedy the aforementioned drawbacks of known cold screens, by proposing a solution making it possible to minimize the influence of parasitic radiation and to limit the cost. Summary of the invention

[0010] To this end, the invention proposes a device for detecting electromagnetic radiation comprising: - a housing comprising a first enclosure and a second sealed and juxtaposed enclosure,

[0011] - a sensor arranged in the first enclosure and formed by a sensitive flat surface said electromagnetic radiation, said sensor having an optical axis centered relative to said sensor, in which:

[0012] - the first enclosure comprises a window transparent to electromagnetic radiation magnetic arranged opposite said sensor and the second enclosure comprises a first window receiving electromagnetic radiation from outside the housing and a second window transparent to electromagnetic radiation and adjacent to the window of the first enclosure, - the second enclosure comprises a cold element comprising a base arranged on the side of the second window of the second enclosure and an end defining a diaphragm arranged on the side of the first window of the second enclosure, the cold element comprising a side wall connecting the base and said end and having a revolution around the optical axis,

[0013] wherein the section of the cold element in each plane comprising the optical axis is a part of an ellipse, the distance between each focus of said ellipse and the optical axis being greater than or equal to the radius of a circumscribed circle of said sensor.

[0014] Thus, the first enclosure can be maintained at a temperature different from the second enclosure in a simple and effective way. In fact, the first enclosure and the second enclosure are thermally sealed to each other. Each enclosure can be cooled to the exact requirement, i.e. to the operating temperature of the sensor or to the cooling temperature of the cold element which is sufficient to limit or even eliminate stray radiation.

[0015] The second window of the second enclosure may be arranged below the window of the first enclosure along the optical axis, such that said second window of the second enclosure and the window of the first enclosure may be superimposed.

[0016] The foci of the ellipse may be arranged in the plane comprising the sensor, in particular located in the sensor or in an area of ​​interest of said sensor.

[0017] The area of ​​interest of the sensor may be a circular or square area included in the sensor. For example, the sensor may have a dimension of 640 pixels * 512 pixels, the area of ​​interest of which may be an inscribed circle of radius 512 pixels.

[0018] The electromagnetic radiation may be infrared radiation, in particular long infrared radiation having a wavelength range between 7 and 14 microns, or mid-infrared radiation having a wavelength range between 3 and 5 microns.

[0019] The sensor may comprise an array of pixels sensitive to electromagnetic radiation.

[0020] In particular, the optical axis may be perpendicular to the surface of the sensor and passing through the center thereof.

[0021] The diaphragm of the cold element can be centered around the optical axis. The cold element makes it possible to limit the flux perceived by each pixel of the sensor to a perception cone whose generator rests on the edge of the diaphragm.

[0022] The circumscribed circle may be the smallest circle in which the sensor fits, or the area of ​​interest of the sensor, in the plane of the sensor.

[0023] The device may comprise a first means for cooling the first enclosure to a first temperature and a second means for cooling the second enclosure to a second temperature. Said first temperature may be lower than said second temperature.

[0024] Indeed, the cold element does not need to be cooled as much as the sensor. This makes it possible to reduce the operating cost, in particular cooling, of the device. In addition, the separation of the sensor and the cold element into two thermally sealed enclosures makes it possible to reduce the time taken to implement cooling to the operating temperature of the sensor and the cold element respectively. Indeed, the device makes it possible not to cool the cold element unnecessarily.

[0025] The first cooling means may be a cooling means based on Stirling cold. The second cooling method can be thermoelectric cooling.

[0026] The first temperature may be between 70K (Kelvin) and 150K, in particular between 80K and 90K, in particular equal to 150 K. The second temperature may be between 170K and 250K, in particular equal to 170K.

[0027] The second cooling means may be arranged between the first window and the cold element.

[0028] The first cooling means may comprise a platform on which the sensor is placed. The sensor may be arranged between the first cooling means and the window of the first enclosure.

[0029] The device may comprise a baffle surrounding the sensor and provided with a diaphragm arranged for the passage of electromagnetic radiation. Said baffle may comprise an internal surface facing the sensor and an opposite external surface. Said external surface may comprise a coating reflecting magnetic radiation. Said internal surface may be a surface having an emissivity close to 1. For example, said internal surface may comprise a matte black coating. The reflective coating may be a mirror or a metal coating, in particular a polished one.

[0030] The baffle may be cylindrical comprising a first open end and arranged at the sensor and surrounding it.

[0031] The diaphragm of the baffle may be arranged at a second end of the baffle opposite the first end.

[0032] Such a baffle makes it possible to limit the parasitic radiation perceived by the sensor.

[0033] The baffle may be cooled by the first cooling means. For example, the first end of the baffle may be placed on the platform of the first cooling means.

[0034] The side wall of the cold element may comprise a coating reflecting magnetic radiation on its internal face facing the sensor.

[0035] The side wall of the cold element may comprise a coating reflecting magnetic radiation on its external face opposite said internal face.

[0036] The reflective coating may be a metallic coating, in particular polished, or a mirror.

[0037] According to one embodiment, the sensor may be rectangular. According to another embodiment, the sensor, or the area of ​​interest of the sensor, may take other shapes such as square or circular.

[0038] The second enclosure may comprise an additional cold element, in particular in addition to the so-called main cold element, arranged between the cold element and the second window. Said additional cold element may comprise a base arranged on the side of the second window of the second enclosure and one end defining a diaphragm arranged on the side of the cold element. The additional cold element may comprise a side wall connecting the base and said end and having a revolution around the optical axis. In particular, the section of the additional cold element in each plane comprising the optical axis may be part of an ellipse, the distance between each focus of said ellipse and the optical axis being greater than or equal to the radius of the circumscribed circle of said sensor, or of the area of ​​interest of the sensor.

[0039] The addition of two cold elements in the second enclosure makes it possible to limit the diameter of the main cold element and thus reduce its height. This makes it possible to reduce the size of the device.

[0040] For example, the additional cold element may be nested within the main cold element.

[0041] Similar to the main cold element, the additional cold element may be centered relative to the optical axis.

[0042] The main cold element may comprise a cylindrical portion at its base. Said elliptical section side wall may connect the end of the cold element to the cylindrical portion. The diameter of the cylindrical portion may be equal to or slightly greater than the external diameter of the base of the additional cold element. The base of the additional cold element is understood to mean the portion having the largest diameter of the additional cold element.

[0043] The additional cold element may have an internal face, facing the sensor, having a coating reflecting magnetic radiation.

[0044] The cold element may be a sheet metal, in particular a metal sheet, with a thickness of less than 200 microns, in particular equal to 100 microns. For example, the main or additional cold element may be formed by stamping sheet metal. The cold element may be made of an aluminum alloy.

[0045] The device may comprise at least one means for vacuuming the first enclosure and / or the second enclosure. Each enclosure may be connected to a vacuuming means. Vacuuming the enclosures makes it possible to reduce convection losses.

[0046] According to one embodiment, the diaphragm may have a circular outline or any other suitable shape.

[0047] The device may be intended in particular to equip self-guided projectile homing devices or thermal cameras, binoculars and night vision goggles, telescopes, and more generally any observation device based on the principle of electromagnetic radiation detection. Brief description of the figures

[0048] [Fig. 1] represents a perspective and partially sectional view of a first exemplary embodiment of a device according to the invention,

[0049] [Fig.2] represents a sectional view of the device of [Fig. 1],

[0050] [Fig.3] represents a perspective view of a cold element equipping the device figures 1 and 2,

[0051] [Fig.4] Figure 4a represents a section in a plane passing through the axis of revolution of the cold element of [Fig.3], and Figure 4b represents a perspective view of a plurality of sections in different planes passing through the axis of revolution of the cold element of [Fig.3].

[0052] [Fig.5] represents a sectional view of a second exemplary embodiment of a device according to the invention. Detailed description of the invention

[0053] Figures 1 and 2 represent a first example embodiment of a device 100 for detecting electromagnetic radiation. The electromagnetic radiation is advantageously infrared radiation, in particular long infrared radiation having a wavelength range of between 7 and 14 microns, or mid-infrared radiation having a wavelength range of between 3 and 5 microns.

[0054] The device 100 comprises a first enclosure 102 and a second enclosure 104. Each of the enclosures 102 and 104 is sealed, in particular thermally sealed. The device comprises at least one vacuum means connected by connections 106 and 108 to the first enclosure 102 and the second enclosure 104, respectively. In particular, a vacuum means is provided for each enclosure 102 and 104.

[0055] The second enclosure 104 comprises a cylindrical side wall hermetically closed by an upper wall 110 and a lower wall 112. The upper wall 110 is provided with an upper window 111 receiving the electromagnetic radiation from outside the device 100 and the lower wall 112 is provided with a lower window 113. Said windows 111 and 113 are transparent to the electromagnetic radiation.

[0056] The first enclosure 102 is delimited by a cylindrical side wall, an upper wall 114 and a lower wall 116 carried by a support 117 of the device 100. The upper wall 114 comprises a window 115 transparent to electromagnetic radiation and adjacent to the window 113 of the second enclosure 104. In particular, the window 115 of the first enclosure 102 and the window 115 of the second enclosure 104 have the same dimensions, namely the same diameters and thicknesses.

[0057] In the figures, the windows 111, 113 and 115 have a circular outline but may have other outline shapes, for example rectangular, square, etc.

[0058] The support 117 of the device 100 is connected to a fixing means 118 allowing the device 100 to be mounted on any suitable device such as a camera body, binoculars, a telescope, etc.

[0059] The first enclosure 102 further comprises a sensor 120 having a surface comprising a matrix of pixels sensitive to electromagnetic radiation. The sensor 120 has an optical axis X perpendicular to the surface of the sensor 120 and passing through the center thereof. The sensor 120 is positioned on a platform 122 cooled by a first suitable cooling means 124. The first cooling means 124 may comprise a finger carrying the platform 122 and cooled by the Stirling effect.

[0060] The first cooling means 124 is configured to cool the sensor 120 to a first temperature T1 between 70K and 150K.

[0061] The first enclosure 102 also comprises a baffle 126 having a cylindrical side wall and an upper wall provided with a diaphragm facing the sensor 120. The baffle 126 comprises an open base arranged at the level of the sensor 120 and surrounding the latter. The baffle 126, in particular its diaphragm, is centered around the optical axis X.

[0062] The inner surface of the baffle 126, the one facing the sensor 120, comprises a matte black coating. A matte black coating is understood to mean any surface having an emissivity close to 1. The outer surface of the baffle 126 comprises a coating reflecting magnetic radiation, for example a polished or mirrored metal coating.

[0063] Such a baffle 126 makes it possible to limit the parasitic radiation perceived by the sensor 120.

[0064] The base of the baffle 126 is placed on the platform 122 of the first cooling means. dissement 124, which makes it possible to cool the baffle 126 in operation and to reduce parasitic radiation coming from the baffle 126.

[0065] To reduce incident rays from off-field sources, the second enclosure 104 comprises a cold element 128, shown in more detail in Figures 3 and 4. The cold element 128 comprises a base 128-14 placed on the lower wall 112 of the second enclosure 104 and a diaphragm 128-12, formed by an opening at the upper end of the cold element 128, that on the side of the upper wall 110 of the second enclosure 104. The diaphragm 128-12 allows the passage of electromagnetic radiation. A side wall 128-10 connects the base 128-14 to the diaphragm 128-12.

[0066] The diaphragm of the baffle 126 and the diaphragm 128-12 of the cold element 128 limit the flow perceived by the sensor 120 and thus define the field of vision 127 of the sensor 120.

[0067] The diaphragm of the baffle 126 and the diaphragm 128-12 are centered around the optical axis X.

[0068] The cold element 128 is cooled by a second cooling means 130 arranged between the upper wall 110 of the second enclosure 104 and the cold element 128. The second cooling means 130 cools the cold element 128 to a second temperature between 170K and 250K. The second cooling means 130 is a thermoelectric cooling means.

[0069] The second cooling means 130 comprises an annular part held by flats 128-16 arranged at the upper level of the side wall 128-10 of the cold element 128. The flats 128-16 may be 4 in number and distributed circumferentially around the optical axis X. The flats 128-16 are rigid but may be flexible.

[0070] Alternatively, the flats 128-16 may be replaced by a curved surface.

[0071] The cold element 128 does not need to be cooled as much as the sensor 120 for ensure the limitation of stray radiation. The use of two separate and independently cooled enclosures makes it possible to reduce the operating cost, in particular the cost of cooling, of the device and to reduce the time taken to implement cooling to the operating temperature of the sensor 120 and the cold element 128 respectively.

[0072] Furthermore, the section 128-18 of the cold element 128 in each plane comprising the optical axis X is a part of an ellipse as shown in FIG. 4a. The foci f1 and f2 of said ellipse are arranged so that the distance between each focus f1 and f2 and the optical axis X is greater than or equal to the radius of a circumscribed circle 123 of the sensor 120. The circumscribed circle 123 is the smallest circle in which the sensor 120 or an area of ​​interest of the sensor is inscribed, i.e. the circle passing through all the vertices of the sensor 120 or through all the vertices of the area of ​​interest of the sensor 120.

[0073] The foci f1 and f2 are arranged in the plane of the sensor 120, in particular in the surface defined by the sensor 120.

[0074] Alternatively, the foci f1 and f2 may be arranged outside the plane of the sensor 120, for example in an upper half-space defined by the plane of the sensor and oriented towards the upper wall of the diaphragm 126. The upper half-space is further delimited by a frustoconical wall connecting the periphery of the diaphragm 126 and the circumscribed circle 123 of the sensor 120.

[0075] The foci f1 and f2 can also be arranged outside the plane of the sensor 120, for example in a lower half-space opposite the upper half-space relative to the plane of the sensor 120.

[0076] The sensor 120 is rectangular but can take other shapes such as circular, square, triangular, etc.

[0077] All the rays passing between the foci of the ellipse and reflecting on the ellipse pass back between the two foci of said ellipse. Thus, the shape of the cold element 128 allows each radiation 131 coming from the circle defined by the rotation around the optical axis of the foci to be reflected on the ellipse and return to said circle.

[0078] The second enclosure 204 comprises a porthole 129 arranged on the diaphragm 128-12 and can be any type of lens.

[0079] The side wall 128-10 comprises a magnetic radiation-reflecting coating on its inner face.

[0080] The side wall 128-10 comprises a magnetic radiation-reflecting coating on its external face.

[0081] [Fig. 5] represents a second exemplary embodiment of a device 200 according to the invention. The device 200 comprises the same elements as the device 100. Unlike, the device 200 comprises a first cold element 202 and a second cold element 204 nested in the first cold element 202.

[0082] The first cold element 202, similarly to the cold element 128, comprises a base 202-14, a diaphragm 202-12 and a side wall 202-10 connecting the base 202-14 to the diaphragm 202-12.

[0083] The second cold element 204 also comprises a base 204-14, a diaphragm 204-12 and a side wall 204-10 connecting the base 204-14 to the diaphragm 204-12.

[0084] Each of the side wall 202-10 and the side wall 204-10 has in each plane comprising the optical axis X a section having a part of an ellipse. The foci of said ellipse are arranged so that the distance between each focus and the optical axis X is greater than or equal to the radius of the circumscribed circle 123 of the sensor 120.

[0085] The superposition of two cold elements 202 and 204 makes it possible to reduce the diameter of the base 202-14 of the first cold element 202. In particular, the base 202-14 is cylindrical and has a diameter equal to or slightly greater than the diameter of the base 204-14 of the second cold element 204.

[0086] The height of the second cold element 204, i.e. the distance between the diaphragm 204-12 and the base 204-14, is less than the height of the first cold element 202, i.e. the distance between the diaphragm 202-12 and the base 202-14.

[0087] Thus, the first cold element 202 makes it possible to contain the radiation 131 coming from the first cold element 202 and the second cold element 204 makes it possible to contain the radiation 131-1 coming from the second cold element 204.

[0088] The second cooling means 130 is arranged between the first cold element 202 and the upper wall 110 of the second enclosure 204.

[0089] The second cooling means 130 cools the second enclosure 104 and makes it possible to cool each of the first cold element 202 and the second cold element 204.

[0090] The side wall 202-10 of the cold element 202 comprises a reflective coating magnetic radiation on its inner face.

[0091] The side wall 202-10 of the cold element 202 comprises a coating reflecting magnetic radiation on its external face.

[0092] The side wall 204-10 of the cold element 204 comprises a coating reflecting magnetic radiation on its internal face.

[0093] The side wall 204-10 of the cold element 204 comprises a coating reflecting magnetic radiation on its external face.

Claims

Claims

1. Device (100,200) for detecting electromagnetic radiation comprising: - a housing comprising a first enclosure (102) and a second enclosure (104) which are hermetic and juxtaposed, - a sensor (120) arranged in the first enclosure (102) and formed by a flat surface sensitive to said electromagnetic radiation, said sensor having an optical axis (X) centered relative to said sensor (120), in which: - the first enclosure (102) comprises an upper wall (114) provided with a window (115) transparent to electromagnetic radiation arranged opposite said sensor (120) and the second enclosure (104) comprises a first window (111) receiving electromagnetic radiation from outside the housing and a lower wall (112) provided with a second window (113) transparent to electromagnetic radiation and adjacent to the window (115) of the first enclosure, - in the second enclosure (104) is arranged a cold element (128,202) comprising a base (128-14) arranged on the side of the second window (113) of the second enclosure (104) and an end defining a diaphragm (128-12) arranged on the side of the first window (111) of the second enclosure (104), the cold element (128,202) comprising a side wall (128-10) connecting the base (128-14) and said end and having a revolution around the optical axis (X), in which the section (128-18) of the cold element (128,202) in each plane comprising the optical axis (X) is a part of an ellipse, the distance between each focus (fl,f2) of said ellipse and the optical axis (X) being greater than or equal to the radius of a circumscribed circle of said sensor (120).,

2. Device (100,200) according to claim 1, comprising a first means (124) for cooling the first enclosure (102) to a first temperature and a second means (130) for cooling the second enclosure (104) to a second temperature, said first temperature being lower than said second temperature.

3. Device (100,200) according to claim 1 or 2, comprising a baffle (126) surrounding the sensor (120) and provided with a diaphragm arranged for the passage of electromagnetic radiation, said baffle (126) comprising an internal surface facing the sensor (120) and an opposite external surface, said external surface comprising a re- clothing reflecting magnetic radiation.

4. Device (100,200) according to one of the preceding claims, in which the side wall (128-10) of the cold element (128) comprises a coating reflecting the magnetic radiation on its internal face facing the sensor (120).

5. Device (100,200) according to claim 4, wherein the side wall (128-10) of the cold element (128) comprises a coating reflecting magnetic radiation on its external face opposite said internal face.

6. Device (100,200) according to one of the preceding claims, in which the sensor (120) is rectangular in shape.

7. Device (200) according to one of the preceding claims, wherein the second enclosure (104) comprises an additional cold element (204) arranged between the cold element (202) and the second window (113), said additional cold element (204) comprising a base (204-14) arranged on the side of the second window of the second enclosure (104) and an end defining a diaphragm (204-12) arranged on the side of the cold element, the additional cold element (204) comprising a side wall (204-10) connecting the base and said end and having a revolution around the optical axis (X), the section of the additional cold element (204) in each plane comprising the optical axis (X) is a part of an ellipse, the distance between each focus of said ellipse and the optical axis being greater than or equal to the radius of the circumscribed circle of said sensor (120).

8. Device (200) according to the preceding claim, wherein the cold element (202) comprises a cylindrical part at its base (202-14), said lateral wall with elliptical section connecting the end (202-12) of the cold element (202) to the cylindrical part (202-14).

9. Device (100,200) according to one of claims 2 to 8, wherein the first temperature is between 70K and 150K and the second temperature is between 170K and 250K.

10. Device (100,200) according to one of the preceding claims, in which the cold element (128,202,204) is a sheet metal with a thickness of less than 200 microns, in particular equal to 100 microns.

11. Device (100,200) according to one of the preceding claims, comprising at least one means for placing the first enclosure (102) and / or the second enclosure (104) under vacuum.

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