DE102004040373B4 - Heat insulating unit for a detector and its use - Google Patents

Abstract

The invention relates to a heat insulating unit (27) for a detector (20), comprising a heat insulating housing (16) with a window (18) and a detector (20) arranged inside the housing (16). In the housing of the heat insulating unit (12) is located between the window (18) and the detector (20) has an optical system (28) for forming an object scene on the detector (20). DOLLAR A Furthermore, the invention relates to the use of a Wärmeisoliereinheit (27) as a second stage (44) in a two-stage imaging optics (42).

Description

The The invention relates to a heat insulating unit for one Detector and its use.

It is known to detectors, such as semiconductor detectors based on HgCdTe, PtSi and InSb as well as so-called QWIPs (quantum well infrared photo detectors), their optimal radiation sensitivity reach only at temperatures far below room temperature. Therefore, a cooling The detectors necessary to ensure a rapid and lasting cooling effect To reach the detectors are usually in a Wärmeisoliereinheit arranged. For this purpose, often double-walled, evacuated housing with a radiation-transmissive Window inserted.

In Thermography becomes such thermal insulation units for one Detector together with an attachment optics to a camera or imaging system combined. Under an imaging system in the sense of the application is a detector with an optical system in front (attachment optics) understood that for the imaging of object scenes on the detector provides. In the industry For example, thermography is used to produce products or Installations on overheating or subcooling to check. In The science is the thermography among others in the fields Climate research and medicine used. Thermography is used in the military sector for terrain exploration and education.

Unfortunately, needed an imaging system according to the state sufficient space for both the thermal insulation unit of the detector as well as for the associated imaging intent optics.

From the US Pat. No. 6,444,984 B1 For example, a cryogenic optical filter system for a detector is known. Here, in a sealed housing, a detector in front of which a cooled, transmissive substrate is arranged, which serves as a filter. In order to be able to map targets on the Dektektor, an optical system for focusing is arranged in front of the housing.

In the Patent Abstracts of Japan JP 61194323 A a radiation thermometer is described in which an accurate temperature measurement is to be achieved by a filter and a lens are connected upstream of an uncooled detector housing whose one end face is formed by a filter element.

It The object of the present invention is a heat insulating unit for one Specify detector that allows a compact design. Next lies The invention is based on the object, a technical use of a such Wärmeisoliereinheit specify.

The the first object is achieved by a heat insulating unit for a Detector solved, in accordance with the invention in one heat-insulating casing with a window between this window and the inside of the housing arranged, cooled Detector an optical system for imaging an object scene on the detector is arranged.

Thereby, in that in any case required Wärmeisoliereinheit for a Detector disposed an optic between the window in the housing and the detector becomes, even in the smallest space is a functional Imaging system realized. This will easily the for the Realization of a thermal insulation unit required space ideally exploited. The imaging optics is located Thus, by the construction in the Wärmeisoliereinheit in a small Distance to the detector. This allows the optics with respect to their geometric dimensions kept small. This brings as another positive aspect a cost saving with it.

By doing an optic in the housing the heat insulating unit is introduced, the temperature of the optics can be kept stable become. Since the refractive power of an optic is temperature-dependent, this is synonymous with the fixation of the focal point of Optics at a fixed position. After a single adjustment of the detector in terms of optics is thus always an optimal imaging behavior guaranteed on the detector. Such a heat insulating unit is therefore particularly suitable for a use under extreme conditions in terms of temperature without being impaired have to accept in terms of imaging behavior. On costly and expensive activities For temperature stabilization of the optics can be omitted.

Depending on the requirements that depend on the quality of the illustrations of the object scenes may be placed on the detector, it may even be possible, completely on another optics, which is outside the case in front the window is to be omitted.

In an advantageous variant, the optics in the heat insulating unit are designed as a cold filter. In Wärmeisoliereinheiten are usually standard cold filters included. A cold filter is an optical filter that is located in front of the detector and is used behind block radiation outside a desired wavelength range, thus reducing the noise. In practice, such filters are thin plates made of a suitable optical material which is transparent to the spectral region of interest, with a mostly two-sided coating. Since a corresponding material can also be used for the optics, the coated filter plate can be easily replaced by a coated optic. As a result, the positive properties of a cold filter are ideally combined with the imaging properties of the optics. The space is skilfully exploited by the cold filter is simply replaced by the "cold filter optics".

Conveniently, is the optics of the heat insulating unit a lens or a lens system. A lens is one of two surfaces, either spherical or aspheric could be, limited body with a defined refractive effect. The lens changes the opening angle of a beam and has imaging properties. Characteristic for the imaging properties the lens is the focal length. Because every picture is through a lens are subject to aberrations, often several different Lenses combined into a lens system, thereby reducing the aberrations to reduce. The shape of the lens or the lens system is chosen so that in a particular arrangement of the lens or the lens system inside the case the heat insulating unit in front of the detector optimal imaging properties of an object scene be reached on the detector. By the two side surfaces of the Lens or the lens system still occupied with cold filter layers can minimize the background noise of unwanted radiation and thereby the picture quality further increased become.

Preferably is the optics on one in the housing the heat insulating unit attached cold shield attached. This panel is is a device for mechanically limiting the beam of the optical image on the one hand and for blocking thermal radiation on the other hand. For this reason, the cold shutter is a thin, thermal conductive Material used. It can be at the cold aperture to a disc with an opening therein act. The cold shield is in thermal contact with the detector to have the same temperature as this one. Depending on the geometric design, the cold shield can also serve laterally incident stray light or thermal radiation on the Hide the detector. The cold shield can be a kind of housing within of the housing the heat insulating unit - without however to exhibit a thermal-mechanical contact to this - represent. This inner case has at its one end face an opening on, facing each other the window in the housing the heat insulating unit located. The other end is completely or partially through the detector surface educated.

The Optics will ideally be within the chiller in a suitable Distance fixed in front of the detector. As a result, the optics is also protected from external temperature influences the cold shield protected. Ideally, for the attachment of the optics to the cold shield is a thermally conductive material used. As a result, the optics is also in contact via the cold diaphragm with the chilled Detector. This ensures a stable temperature of the optics and temperature-dependent Shifts of the focal plane of the optics due to a temperature-related change the refractive power of the material of which the optics consists prevents. A temperature compensation as required in conventional Op tikbaugruppen is, unnecessary with it. In case of misalignment between optics and detector due to a wrong choice Distance can solve this problem by changing the temperature the detector and thus the optics to a certain extent fixed be, since thereby the refractive power of the optics and thus the position of the associated Focal plane can be influenced.

In a further advantageous embodiment of the invention is a the surface facing the detector the optics such a curved Given shaping, giving a back reflection of radiation from the detector is diffused. By a corresponding remuneration of the Detector and the surface the optics, which faces the detector, by means of anti-reflection coatings it can not be prevented that radiation from the detector reflects will and until the opposite face the cold diaphragm arrives and from there again reflects back to the detector becomes. This reflected radiation is then blurred and leads for generating so-called ghost images on the detector, which the Falsify the image of an object scene. By a corresponding curvature the area The optics, which faces the detector, but the emergence suppressed by ghosting become. By this measure the image field can be chosen like this Be that ghost of the desired object scene far away lies and thus does not bother anymore. specially the generation of ghost images caused by laser irradiation can be avoided.

It is also advantageous that the window in the housing of the heat insulating unit comprises a nonlinear optical material. If high-intensity laser radiation falls on a detector, this can lead to impairment of its functionality and in the worst case to a total failure. However, if the laser radiation has to pass through a non-linear optical material, an interaction between the laser beam and the window material will occur, which prevents the radiation destroying the detector from falling on it. By thus constructed Wärmeisoliereinheit a long life of the detector is favored.

The second task with regard to a technical use is achieved by the use of the thermal insulation unit as a second stage in a two-tier imaging system. in this connection can use the first level for flexible adaptation of the visual field without changing the second stage heat exchanger unit to have to make. Depending on the application, by appropriate choice of the first Stage the desired Mapping scale achieved become.

It It can be provided that as a first stage different attachment optics, which can be swung in succession or in combination provided are. An attachment optics can be used, for example, as a Galileo telescope accomplished be. Conveniently, then, the detector is the Wärmeisoliereinheit an easily replaceable detector or a dual-band detector unit, such as a QWIP that works for two spectral ranges such as Mid-Wave (three to five Micrometer) and long-wave (eight to twelve microns) sensitive is. This can easily a spectral broadband imaging system will be realized.

Also a two-stage imaging system comprising a thermal ic unit for one Detector for a spectral range around 1.5 μm as a second stage and a corresponding first stage, which at the same time of a laser detector or receiver and an eye-safe laser transmitter of the same spectral range is used, is conceivable.

Farther it is imaginable, in the beam path of the first stage an adaptive Optical part in the form of mutually displaceable or tiltable To introduce prism or lens units, which makes it possible a visual line stabilization within a few pixel fields of view to reach the detector.

Especially it is advantageous if the Wärmeisoliereinheit with respect to a first stage is arranged so that its cold shutter with the exit pupil of this first stage of the two-stage imaging system to coincide. In this case you get a radiometrically optimized system, which has a very high coldplate efficiency close to one is reached, because the proportion of false light is particularly good repressed becomes. Foreign radiation components within the housing of the Wärmeisoliereinheit, in particular within the cold shutter, caused by z. B. laser and solar radiation are largely avoided.

Conveniently, the use looks like that after the first stage a real Intermediate image immediately before or in the window of the thermal insulation unit arises. Immediately in front of the window here means an area of a few millimeters. This real intermediate image allows the introduction a field stop, which in the area of the window in the housing of the Wärmeisoliereinheit lies. A field diaphragm is used for the targeted restriction of the Image field and thereby allows, for example, even objects to be able to perceive strong in the vicinity Light sources are located. Conveniently, by introducing the Field also the size of the window in the case the Wärmeisoliereinheit reduced become. This is not only a cost advantage, but There will also be a higher density of the housing caused by the peripheral reduced seams between the window and housing.

The Wärmeisoliereinheit is particularly suitable for use in a seeker head. Sighting heads for guided missiles usually contain an electrodynamically moving frame system in which optical systems are integrated. The two-stage imaging optics with the heat insulation unit as a second stage can be integrated into such an optical system. About the Frame system is now the possibility a line of sight tracking or -Motion given.

Farther it is conceivable the Wärmeisoliereinheit to use in devices with a sensor for reconnaissance in a predefined area using the detector for specific objects to seek to identify or identify them.

Also a use of the heat insulating unit comes in devices with a sensor for monitoring and warning in question. In this case, a space area is permanently monitored by means of the detector with the goal of change to detect the state of the space area and, where appropriate to issue a message of a specific threat.

embodiments The invention will be explained in more detail with reference to a drawing. It shows

1 FIG. 2 schematically shows the construction of a prior art imaging system, comprising a front lens and a thermal insulation unit, FIG.

2 schematically the construction of a heat insulating unit with optics,

3 schematically the design of an optic for a heat insulating unit,

4 schematically the design of an optic in the form of a lens system for a Wärmeisoliereinheit and

5 a two-stage imaging optics with a Wärmeisoliereinheit as a second stage.

Same Parts are designated by the same reference numerals.

In 1 is the construction of an imaging system 10 shown schematically according to the prior art. The imaging system 10 has a Wärmeisoliereinheit 12 and a separate attachment optics 14 on. The heat insulating unit 12 includes a heat-insulating housing 16 with a window 18 , which consists of a radiation-transparent material and an end face of the detector 20 forms. Inside the case 16 is a detector 20 arranged. The detector 20 is opposite the window 18 on the other end of the case 16 and is concentric with the surface of the window 18 aligned. Inside the case 16 there is a cold shutter 22 , which is designed in the form of an inner housing, one end face of which is an opening 24 which is concentric with the window 18 and to the detector 20 and the other end is in thermal-mechanical contact with the detector 20 located. To the housing 16 the heat insulating unit 12 however, there is no contact. The cold shutter 22 consists of a thin nickel sheet.

Inside the cold shutter 22 there is a cold filter 25 , The cold filter 25 is at the cold shutter 22 attached. The attachment can, for example, by inserting into one in the cold shield 22 intended mount, soldering, gluing or other techniques in question. By attaching the cold filter 25 at the cold shutter 22 creates a thermal contact between the two. The cold filter 25 can be made of a thin germanium, silicon or sapphire plate with a double-sided coating 26 consist. As coatings 26 Layers of magnesium fluoride are known only to the spectral range for which the detector 20 is sensitive, permeable and largely impermeable to the rest of the spectral range. By doing that, the detector 20 cooled from the back, are also associated with this cold-stop 22 and the cold filter 25 co-cooled, reducing the radiation load due to the thermal emission of cold shield 22 and cold filter 25 is minimized.

2 shows a Wärmeisoliereinheit 27 with an integrated look 28 , The optics 28 is here within the housing of the cold shield 22 between the window 18 and the detector 20 arranged. As a result, an extremely small-scale imaging system is realized. In the optics 28 This is a lens in this embodiment 30 , which consists of germanium. The Lens 30 has cold-filter coatings adapted on both sides to the spectral region of the detector 26 and thereby replaces the in 1 shown cold filter 25 and at the same time fulfills imaging properties. When fixing the optics 28 at the cold shutter 22 Care should be taken that this is thermally conductive to the optics 28 to the same temperature as the cold shutter 22 and the detector 20 to bring and keep on this. This fixes their focal plane for optimal imaging behavior. The optics 28 is at the cold shutter 22 fixed so that they are at a suitable distance from the detector 20 located. Small distance errors can be caused by a temperature change, which is equivalent to the change in refractive power of the optical material from which the optics 28 exists, be corrected.

3 schematically shows the design of an optic 28 for a thermal ic unit 27 , The illustrated design is optimized for a wavelength range of three to five microns; however, depending on the application, it can easily be modified for other spectral ranges. You can see the beam path through the opening 24 the cold shutter 22 falling beam acting as a cold filter 25 trained germanium lens 34 meets and on the detector 20 is focused. The illustrated cold filter germanium lens 34 is designed as a refractive-diffractive doublet. Its focal length is 20 mm with an F-number (aperture number) of two and its numerical aperture NA 0.25. The curvature of the lens 34 is chosen so that a return reflex from the detector 20 is diffused.

Application specific is a change in the focal length within the length of the housing 16 the heat insulating unit 27 specified range and the F-number (opening number) possible. Conveniently, the design can also be scaled so that the size of the image matches the sensitive area of the detector 20 matches. It makes sense, the design of the operation of the Wärmeisoliereinheit 27 to adapt to prevailing temperature.

4 schematically shows the design of an optic 28 comprising a lens system 36 from two lenses 38 and 40 , for a thermal insulation unit 27 , This points to the opening 24 the cold shutter 22 facing side of the convex lens 38 and the detector 20 facing side of the concave lens 40 a cold filter coating 26 on. The lens system 36 has a focal length of 20 mm and a numerical aperture NA of 0.2. By adding a concave lens 40 to the convex lens 38 can the diffractive effect of the lens 38 be avoided. The two lenses 38 . 40 are in direct contact with each other. However, it may also be provided a certain distance between the lenses.

In 5 is schematically a two-stage imaging optics 42 shown. The second stage 44 is in this case of a Wärmeisoliereinheit 27 educated. The construction of the first stage 46 is not shown in detail. For example, this may be a primary objective, which is used to image an object scene onto an intermediate image plane 48 serves. This can be composed of various optical elements. The arrangement of the two stages 44 . 46 it is usefully chosen to each other so that the exit pupil of the first stage 46 with the opening 24 the cold shutter 22 coincides. Furthermore, the arrangement of the two stages 44 . 46 selected such that the intermediate image plane 48 in the area of the window 18 the heat insulating unit 27 lies. The heat insulating unit 27 with their optics 28 fulfills the function of a secondary objective and forms the one in the intermediate image plane 48 resulting image of an object scene on the detector 20 from. For clarification is in 5 the principal course of an optical path drawn. It is conceivable between the first stage 46 and in the area of the window 18 to arrange other optical elements, such as diaphragms or filters.

10

imaging system

12

Wärmeisoliereinheit

14

optical head

16

casing

18

window

20

detector

22

cold panel

24

opening

25

Cooling filter

26

Cold filter coating

27

Wärmeisoliereinheit with optics

28

optics

30

lens

34

Cold Filter germanium lens

36

lens system

38

lens

40

lens

42

two-step imaging system

44

second step

46

first step

48

Intermediate image plane

Claims (10)

Heat insulating unit ( 27 ) for a detector ( 20 ) comprising a heat-insulating housing ( 16 ) with a window ( 18 ) and the inside of the housing ( 16 ), cooled detector ( 20 ), wherein in the housing ( 16 ) between the window ( 18 ) and the detector ( 20 ) an optic ( 28 ) for imaging an object scene on the detector ( 20 ) is arranged. Heat insulating unit ( 27 ) according to claim 1, wherein the optics ( 28 ) as a cold filter ( 25 ) is designed. Heat insulating unit ( 27 ) according to claim 1 or 2, wherein the optics ( 28 ) around a lens ( 30 ) or a lens system ( 36 ). Heat insulating unit ( 27 ) according to one of claims 1 to 3, wherein the optics ( 28 ) at one in the housing ( 16 ) cold blende ( 22 ) is attached. Heat insulating unit ( 27 ) according to one of the preceding claims, wherein one of the detectors ( 20 ) facing surface of the optics ( 28 ) has a curved shape such that a back reflection from the detector ( 20 ) is diffused. Heat insulating unit ( 27 ) according to one of the preceding claims, wherein the window ( 18 ) comprises a nonlinear optical material. Use of a thermal insulation unit ( 27 ) according to one of the preceding claims as a second stage ( 44 ) in a two-stage imaging system ( 42 ). Use of the thermal insulation unit ( 27 ) according to claim 7, wherein the thermal insulation unit ( 27 ) in the two-stage imaging system ( 42 ) is arranged such that the cold diaphragm ( 22 ) with the exit pupil of a first stage ( 46 ) of the two-stage imaging system ( 42 ) coincides. Use of the thermal insulation unit ( 27 ) according to claim 7 or 8 such that after the first stage ( 46 ) a real intermediate image immediately before or in the window ( 18 ) of the thermal insulation unit ( 27 ) arises. Use of the thermal insulation unit ( 27 ) according to one of the preceding claims 7 to 9 in a seeker head.