Integrated structure adopting pulse tube refrigerator to cool infrared detector

Abstract

The invention discloses an integrated structure for cooling an infrared detector by adopting a pulse tube refrigerator, and particularly relates to the field of refrigeration and low-temperature engineering, the integrated structure comprises a bottom plate, a compressor and the pulse tube refrigerator are respectively arranged on two sides of the top of the bottom plate, and a connecting tube is arranged between the compressor and the pulse tube refrigerator; the compressor and the pulse tube refrigerator are combined into a whole through a connecting pipe, an infrared detector is arranged on one side of the pulse tube refrigerator, and a Dewar tank is connected between the infrared detector and the pulse tube refrigerator. According to the invention, the infrared detector is installed at the cold end part of the pulse tube refrigerator in a direct coupling manner, and the adverse effect of plastic deformation of the cold end part under a large temperature gradient on the infrared detector is reduced by using the material characteristics of the Kovar bottom plate welded on the cold head; a set of detachable simple Dewar provided with an optical filter, a temperature and data signal transmission interface and a vacuum interface is manufactured, various elements required by operation of the infrared detector are combined together, and diversification and convenience of operation and maintenance are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of refrigeration and cryogenic engineering. More specifically, the present invention relates to an integrated structure for cooling an infrared detector using a pulse tube refrigerator. Background Art

[0002] The pulse tube refrigerator is a major innovation of the regenerative cryogenic refrigerator. It completely eliminates the moving parts at the cold end, thus having significant advantages such as low vibration, low interference, and long life. As an important optoelectronic detection device, in order to achieve a high signal-to-noise ratio, an infrared detector often has very strict requirements on the vibration and interference levels of the supporting refrigerator, and also requires a long continuous working life in some special working scenarios. Therefore, the pulse tube refrigerator is an ideal refrigeration source for infrared detectors.

[0003] When using a pulse tube refrigerator to cool an infrared detector, there are currently some coupling structure forms. However, most structures do not fully utilize the natural advantage that the cold end of the pulse tube refrigerator is a completely passive component, and there are many indirect components, which makes the cold end packaging complicated and is not conducive to the wide application of the pulse tube refrigerator in the field of infrared detectors.

[0004] Therefore, how to design an integrated structure that fully utilizes the advantages of the cold end structure of the pulse tube refrigerator and thus efficiently couples with the infrared detector has become a technical problem that needs to be urgently solved at present. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, an embodiment of the present invention provides an integrated structure for cooling an infrared detector using a pulse tube refrigerator. The technical problem to be solved by the present invention is: how to improve the cold end structure of the pulse tube refrigerator to efficiently couple it with the infrared detector and provide a stable and reliable experimental test environment.

[0006] To achieve the above object, the present invention provides the following technical solution: An integrated structure for cooling an infrared detector using a pulse tube refrigerator, including a bottom plate. On both sides of the top of the bottom plate, a compressor and a pulse tube refrigerator are respectively provided. A connecting pipe is provided between the compressor and the pulse tube refrigerator. The compressor and the pulse tube refrigerator are combined into a whole through the connecting pipe to reduce the slight vibration generated by the compressor during operation transmitted to the pulse tube refrigerator. An infrared detector is provided on one side of the pulse tube refrigerator. A Dewar flask is connected between the infrared detector and the pulse tube refrigerator;

[0007] A lead plug is provided on the outer side of the Dewar flask, and the lead plug is connected to the infrared detector;

[0008] The pulse tube refrigerator includes a phase modulation mechanism, a hot end heat exchanger, and a cold finger. The pulse tube refrigerator is configured as a coaxial structure. A hot end flange is connected between the hot end heat exchanger and the cold finger. The other end of the cold finger is welded and fixed with a cold head, and a kovar base plate is provided at the end of the cold head away from the cold finger.

[0009] In a preferred embodiment, a fixing bracket I is provided between the compressor and the base plate, and a fixing bracket II is provided between the pulse tube refrigerator and the base plate. The fixing bracket I and the fixing bracket II are fixed to the base plate by bolts.

[0010] The Dewar flask is installed on the hot end flange of the pulse tube refrigerator by bolts. The infrared detector is fixed on the end face of the kovar base plate. The kovar base plate is welded to the cold head of the pulse tube refrigerator. The hot end heat exchanger is welded and fixed to the hot end flange. One end of the hot end heat exchanger away from the hot end flange is fixedly connected to the phase modulation mechanism. One end of the cold finger is connected to the hot end flange by laser welding.

[0011] In a preferred embodiment, the Dewar flask is fixed on the hot end flange. Among them, the upper section of the Dewar flask is a detachable vacuum cover, and the lower section is a Dewar outer shell fixed on the hot end flange.

[0012] The vacuum cover is composed of a cover shell, a pressure ring, a gasket, and a filter film. A filter film installation groove is provided at the connection between the top end of the cover shell and the filter film. The gasket is installed at the outer edge of the filter film. The pressure ring is fixed on the upper end face of the vacuum cover of the cover shell by screws and presses the gasket between the cover shell and the filter film to achieve vacuum sealing and fixation of the filter film.

[0013] In a preferred embodiment, the Dewar outer shell is composed of a transition flange, a ceramic lead ring, a main shell, an air extraction interface, and a lead base.

[0014] The air extraction interface and the lead base are respectively welded at the corresponding opening positions of the main shell. The two ends of the ceramic lead ring are respectively connected to the transition flange and the main shell by laser welding to form two laser weld seams.

[0015] The bottom end of the main shell is provided as a Dewar flange. The Dewar flange is vacuum-sealed with the hot end flange through screws and a sealing ring. The lead plug is installed at the lead base position of the main shell.

[0016] A columnar thermometer is inserted into the top end of the cold head and fixed with a low-temperature adhesive. A thermometer lead in the Dewar is connected between the columnar thermometer and the lead plug. A cover shell flange is fixedly provided at the bottom end of the cover shell. The cover shell flange and the transition flange are detachably replaced by means of bolt and sealing ring connection, which is convenient for operating the internal devices of the Dewar flask.

[0017] In a preferred embodiment, the infrared detector is fixed at the central position of the end face of the kovar base plate, and a cold shield is provided on the kovar base plate outside the infrared detector;

[0018] The cold shield is a square thin-walled shell structure. Cold shield support feet are fixedly provided at the bottom ends of the symmetric two sides of the cold shield. Through holes are provided in the cold shield support feet, and threaded holes corresponding to the through holes of the support feet are provided at the top end of the kovar base plate. Cold shield side grooves are made at the lower ends of the remaining two side faces of the cold shield. The infrared detector is completely covered inside the cold shield. A detector lead is provided outside the infrared detector. The detector lead passes through the cold shield side groove and is connected to a ceramic lead ring. A circular cold shield window is provided at the top end of the cold shield housing.

[0019] In a preferred embodiment, outer circular end faces are provided on both sides of the top end of the cold head. A through hole structure for a thermometer socket is horizontally penetrated at the central position of the outer circular end face. The columnar thermometer is installed in the thermometer socket;

[0020] The top end of the cold head is provided with a cold head concave surface for filling brazing material. The kovar base plate is arranged in the cold head concave surface. The kovar base plate is welded to the cold head in a vacuum brazing furnace. The kovar base plate is a circular thin plate structure with parallel end faces on both sides of the outer circle, and the shape of the kovar base plate is adapted to the shape of the cold head concave surface.

[0021] In a preferred embodiment, the inner walls of the vacuum cover, the Dewar shell, and the outer surface of the cold shield are all polished to increase the reflection effect of radiant energy. The inner surface of the cold shield is blackened. The kovar base plate is seamlessly connected to the cold head by vacuum brazing. The upper and lower ends of the ceramic lead ring are respectively connected to the transition flange and the main housing by laser welding, and the sealing performance of the weld is verified.

[0022] Technical effects and advantages of the present invention:

[0023] 1. In the present invention, the compressor and the pulse tube refrigerator are arranged separately, which reduces the vibration interference of the mechanical vibration of the compressor on the cold end of the pulse tube refrigerator; a columnar thermometer inserted into the cold head is used to measure the cold end temperature of the pulse tube refrigerator, increasing the contact area between the thermometer and the cold head, and making the error between the temperature detected by the thermometer and the actual temperature of the cold head smaller;

[0024] 2. In the present invention, a kovar base plate is installed between the cold head and the quantum detector. Since the expansion coefficient of the kovar material is close to that of the detector substrate, in a large temperature gradient environment, the deformation amplitudes of the kovar base plate and the detector substrate are basically the same, ensuring good contact between the two, and making the cold quantity transfer not affected by deformation;

[0025] 3. The cold shield of the present invention completely covers the infrared detector. Its outer surface is polished to increase the reflectivity of external thermal energy, and its inner surface is blackened to absorb the radiation energy reflected from the detector surface. Under the shielding effect of the cold shield, both the cold loss is reduced, and the infrared detector is not easily interfered by stray radiation energy.

[0026] 4. The Dewar of the present invention is made into a split structure. The Dewar outer shell part with a fixed position is equipped with a detector, a thermometer lead external connection facility, and a vacuum interface. The vacuum cover for installing the filter can be disassembled at any time to facilitate the adjustment and replacement of the infrared detector and the cold shield inside the Dewar, increasing the convenience during the experimental operation process. Brief Description of the Drawings

[0027] Figure 1 It is a schematic plan view of the overall structure of the present invention.

[0028] Figure 2 It is a schematic structural diagram of the pulse tube refrigerator of the present invention.

[0029] Figure 3 It is a schematic diagram of the integrated structure inside the Dewar of the present invention.

[0030] Figure 4 It is a sectional view of the Dewar outer shell of the present invention.

[0031] Figure 5 It is a sectional view of the vacuum cover of the present invention.

[0032] Figure 6 It is a sectional view of the cover shell on the vacuum cover of the present invention.

[0033] Figure 7 It is a three-dimensional structure diagram of the cold shield of the present invention.

[0034] Figure 8 It is a three-dimensional structure diagram of the kovar bottom plate of the present invention.

[0035] Figure 9 It is a three-dimensional structure diagram of the cold head of the pulse tube refrigerator of the present invention.

[0036] Figure 10 It is a three-dimensional structure diagram of the ceramic lead ring on the Dewar of the present invention.

[0037] The reference numerals are: 1 compressor, 2 connecting pipe, 3 bottom plate, 4 pulse tube refrigerator, 5 Dewar flask, 6 infrared detector, 7 lead plug, 8 fixing bracket I, 9 fixing bracket II, 10 phase modulation mechanism, 11 hot end heat exchanger, 12 hot end flange, 13 cold finger, 14 cold head, 15 kovar bottom plate, 16 main housing, 17 detector lead, 18 ceramic lead ring, 19 transition flange, 20 housing, 21 pressure ring, 22 washer, 23 filter, 24 cold shield, 25 columnar thermometer, 26 thermometer lead, 27 cold shield window, 28 cold shield side groove, 29 cold shield support leg, 30 support leg through hole, 31 threaded hole, 32 cold head concave surface, 33 thermometer socket, 34 outer circular end face, 35 filter installation groove, 36 upper end face of vacuum housing, 37 housing flange, 38 laser weld seam, 39 air extraction interface, 40 lead base, 41 Dewar flange, 42 Dewar outer shell, 43 vacuum housing. Detailed implementation manner

[0038] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] The present invention provides as Figure 1-2The integrated structure for cooling an infrared detector using a pulse tube refrigerator as shown includes a bottom plate 3. On both sides of the top of the bottom plate 3, a compressor 1 and a pulse tube refrigerator 4 are respectively provided. A connecting pipe 2 is provided between the compressor 1 and the pulse tube refrigerator 4. The compressor 1 and the pulse tube refrigerator 4 are integrated into a whole through the connecting pipe 2 to reduce the slight vibration generated during the operation of the compressor 1 transmitted to the pulse tube refrigerator 4. On one side of the pulse tube refrigerator 4, an infrared detector 6 is provided. A Dewar flask 5 is connected between the infrared detector 6 and the pulse tube refrigerator 4; a lead plug 7 is provided outside the Dewar flask 5, and the lead plug 7 is connected to the infrared detector 6; the pulse tube refrigerator 4 includes a phase modulation mechanism 10, a hot end heat exchanger 11 and a cold finger 13. The pulse tube refrigerator 4 is arranged in a coaxial structure. A hot end flange 12 is connected between the hot end heat exchanger 11 and the cold finger 13. At the other end of the cold finger 13, a cold head 14 is welded and fixed. At one end of the cold head 14 away from the cold finger 13, a kovar bottom plate 15 is provided; a fixing bracket I 8 is provided between the compressor 1 and the bottom plate 3, and a fixing bracket II 9 is provided between the pulse tube refrigerator 4 and the bottom plate 3. The fixing bracket I 8 and the fixing bracket II 9 are fixed to the bottom plate 3 by bolts; the Dewar flask 5 is installed on the hot end flange 12 of the pulse tube refrigerator 4 by bolts. The infrared detector 6 is fixed on the end face of the kovar bottom plate 15. The kovar bottom plate 15 is welded to the cold head 14 of the pulse tube refrigerator 4. The hot end heat exchanger 11 is welded and fixed to the hot end flange 12. One end of the hot end heat exchanger 11 away from the hot end flange 12 is fixedly connected to the phase modulation mechanism 10. One end of the cold finger 13 is connected to the hot end flange 12 by laser welding;

[0040] As Figures 7-10 shown, on both sides of the top end of the cold head 14, an outer circular end face 34 is provided. At the central position of the outer circular end face 34, a through-hole structure of a thermometer socket 33 is horizontally penetrated. A columnar thermometer 25 is installed in the thermometer socket 33; the top end of the cold head 14 is provided with a cold head concave surface 32 for filling brazing material. The kovar bottom plate 15 is arranged in the cold head concave surface 32. The kovar bottom plate 15 is welded to the cold head 14 in a vacuum brazing furnace. The kovar bottom plate 15 is a circular thin plate structure with parallel end faces on both outer circles, and the shape of the kovar bottom plate 15 is adapted to the shape of the cold head concave surface 32; the inner walls of the vacuum cover 43, the Dewar outer shell 42 and the outer surface of the cold screen 24 are all polished to increase the reflection effect of the radiation energy. The inner surface of the cold screen 24 is blackened. The kovar bottom plate 15 is seamlessly connected to the cold head 14 by vacuum brazing. The upper and lower ends of the ceramic lead ring 18 are respectively connected to the transition flange 19 and the main housing 16 by laser welding, and the sealing performance of the weld is verified;

[0041] As Figures 3-6As shown, the Dewar flask 5 is fixed on the hot end flange 12. Among them, the upper section of the Dewar flask 5 is a detachable vacuum cover 43, and the lower section is a Dewar outer shell 42 fixed on the hot end flange 12; the vacuum cover 43 is composed of a cover shell 20, a pressing ring 21, a gasket 22 and a filter 23. A filter installation groove 35 is provided at the connection between the top end of the cover shell 20 and the filter 23. The gasket 22 is installed at the outer edge of the filter 23. The pressing ring 21 is fixed on the upper end face 36 of the vacuum cover of the cover shell 20 by screws, and presses the gasket 22 between the cover shell 20 and the filter 23 to achieve the vacuum sealing and fixation of the filter 23; the Dewar outer shell 42 is composed of a transition flange 19, a ceramic lead ring 18, a main shell 16, an air extraction interface 39 and a lead base 40; the air extraction interface 39 and the lead base 40 are respectively welded at the corresponding opening positions of the main shell 16. The two ends of the ceramic lead ring 18 are respectively connected to the transition flange 19 and the main shell 16 by laser welding to form two laser welding seams 38; the bottom end of the main shell 16 is provided as a Dewar flange 41. The Dewar flange 41 realizes vacuum sealing with the hot end flange 12 through screws and sealing rings. The lead plug 7 is installed at the position of the lead base 40 of the main shell 16; a columnar thermometer 25 is inserted into the top end of the cold head 14 and fixed with a cryogenic adhesive. A thermometer lead 26 in the Dewar 6 is connected between the columnar thermometer 25 and the lead plug 7. A cover shell flange 37 is fixedly provided at the bottom end of the cover shell 20. The cover shell flange 37 and the transition flange 19 are disassembled and replaced by means of bolts and sealing rings, which is convenient for operating the internal devices of the Dewar flask 5; the infrared detector 6 is fixed at the center position of the end face of the kovar base plate 15. A cold shield 24 is provided on the kovar base plate 15 outside the infrared detector 6; the cold shield 24 is a square thin-walled shell structure. Cold shield feet 29 are fixedly provided at the bottom ends of the symmetric sides of the cold shield 24. A through hole 30 is provided on the cold shield feet 29. A threaded hole 31 corresponding to the through hole 30 is provided at the top end of the kovar base plate 15. Cold shield side grooves 28 are made at the lower ends of the remaining two side faces of the cold shield 24. The infrared detector 6 is completely covered inside the cold shield 24. A detector lead 17 is provided outside the infrared detector 6. The detector lead 17 passes through the cold shield side groove 28 and is connected to the ceramic lead ring 18. A circular cold shield window 27 is provided at the top end of the cold shield 24 shell.

[0042] First, fabricate a pulse tube refrigerator with stable performance, including the refrigerator, compressor, and support components. Then, process the remaining components. The inner walls of the vacuum chamber 43, Dewar outer shell 42, and the outer surface of the cold shield 24 are polished to enhance the reflection effect of radiant energy. The inner surface of the cold shield 24 is blackened. The kovar base plate 15 is seamlessly connected to the cold head 14 by vacuum brazing. The columnar thermometer 25 is inserted into the cold head 14 and fixed with low-temperature adhesive. The upper and lower ends of the ceramic lead ring 18 are connected to the transition flange 19 and the housing 16 by laser welding respectively, and the sealing performance of the weld is verified. After all the components to be processed and the purchased accessories are prepared, assemble them in the specified assembly sequence until the assembly of the entire invention device is completed;

[0043] Taking advantage of the characteristics of the pulse tube refrigerator 4, such as small vibration interference and stable working state, directly couple the infrared detector 6 to the cold end of the pulse tube refrigerator 4, so that the infrared detector 6 can be in a state of low-temperature constancy and small external interference. By providing a Dewar flask 5 that matches the infrared detector 6, minimize the cold loss. Introduce a light source to irradiate the sensing area of the infrared detector 6 to enable the generated data signal to be output externally, providing a stable and reliable experimental test environment for the research and development of the infrared detector 6, and having better adaptability in actual operation and later maintenance and correction.

[0044] Finally, several points should be noted: First, in the description of this application, it should be noted that unless otherwise specified and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense, which can be mechanical connection or electrical connection, or the communication inside two components, and can be directly connected. "Upper", "lower", "left", "right", etc. are only used to represent the relative position relationship. When the absolute position of the object being described changes, the relative position relationship may change;

[0045] Second: In the attached drawings of the disclosed embodiments of the present invention, only the structures related to the disclosed embodiments are involved. For other structures, reference can be made to the general design. Without conflict, the same embodiment and different embodiments of the present invention can be combined with each other;

[0046] Finally: The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An integrated structure for cooling an infrared detector using a pulse tube refrigerator, comprising a bottom plate (3), characterized in that: On both sides of the top of the bottom plate (3), a compressor (1) and a pulse tube refrigerator (4) are respectively provided. A connecting pipe (2) is provided between the compressor (1) and the pulse tube refrigerator (4). The compressor (1) and the pulse tube refrigerator (4) are integrated into a whole through the connecting pipe (2). On one side of the pulse tube refrigerator (4), an infrared detector (6) is provided. A Dewar flask (5) is connected between the infrared detector (6) and the pulse tube refrigerator (4); A lead plug (7) is provided on the outer side of the Dewar flask (5), and the lead plug (7) is connected to the infrared detector (6); The pulse tube refrigerator (4) includes a phase modulation mechanism (10), a hot end heat exchanger (11) and a cold finger (13). A hot end flange (12) is connected between the hot end heat exchanger (11) and the cold finger (13). The other end of the cold finger (13) is welded and fixed with a cold head (14). A kovar bottom plate (15) is provided at one end of the cold head (14) away from the cold finger (13).

2. The integrated structure for cooling an infrared detector using a pulse tube refrigerator according to claim 1, wherein: A fixing bracket I (8) is provided between the compressor (1) and the bottom plate (3). A fixing bracket II (9) is provided between the pulse tube refrigerator (4) and the bottom plate (3). The fixing bracket I (8) and the fixing bracket II (9) are fixed to the bottom plate (3) by bolts; The Dewar flask (5) is installed on the hot end flange (12) of the pulse tube refrigerator (4) by bolts. The infrared detector (6) is fixed on the end face of the kovar bottom plate (15). The kovar bottom plate (15) is welded to the cold head (14) of the pulse tube refrigerator (4). The hot end heat exchanger (11) is welded and fixed to the hot end flange (12). One end of the hot end heat exchanger (11) away from the hot end flange (12) is fixedly connected to the phase modulation mechanism (10). One end of the cold finger (13) is connected to the hot end flange (12) by laser welding.

3. The integrated structure for cooling an infrared detector using a pulse tube refrigerator according to claim 1, wherein: The Dewar flask (5) is fixed on the hot end flange (12). Among them, the upper section of the Dewar flask (5) is a detachable vacuum cover (43), and the lower section is a Dewar outer shell (42) fixed on the hot end flange (12); The vacuum cover (43) is composed of a cover shell (20), a pressure ring (21), a gasket (22) and a filter film (23). A filter film installation groove (35) is opened at the connection between the top end of the cover shell (20) and the filter film (23). The gasket (22) is installed at the outer edge of the filter film (23). The pressure ring (21) is fixed on the upper end face (36) of the vacuum cover of the cover shell (20) by screws, and the gasket (22) between the cover shell (20) and the filter film (23) is pressed to realize the vacuum sealing and fixing of the filter film (23).

4. The integrated structure for cooling an infrared detector by using a pulse tube refrigerator according to claim 3, wherein: The Dewar outer shell (42) is composed of a transition flange (19), a ceramic lead ring (18), a main shell (16), an air extraction interface (39) and a lead base (40); The air extraction interface (39) and the lead base (40) are respectively welded at the corresponding opening positions of the main shell (16). The two ends of the ceramic lead ring (18) are respectively connected to the transition flange (19) and the main shell (16) by laser welding to form two laser welding seams (38); The bottom end of the main housing (16) is provided as a Dewar flange (41), and the Dewar flange (41) is vacuum-sealed with the hot-end flange (12) through screws and sealing rings. The lead plug (7) is installed at the position of the lead base (40) of the main housing (16). A columnar thermometer (25) is inserted into the top end inside the cold head (14). A thermometer lead (26) located inside the Dewar (6) is connected between the columnar thermometer (25) and the lead plug (7). The bottom end of the cover housing (20) is fixedly provided with a cover housing flange (37).

5. The integrated structure for cooling an infrared detector using a pulse tube refrigerator according to claim 4, characterized in that: The infrared detector (6) is fixed at the central position of the end face of the kovar base plate (15). A cold shield (24) is provided on the kovar base plate (15) outside the infrared detector (6). The cold shield (24) is a square thin-walled housing structure. Cold shield feet (29) are fixedly provided at the bottom ends of the two symmetric sides of the cold shield (24). Through holes (30) are formed in the cold shield feet (29). Threaded holes (31) corresponding to the through holes (30) are formed at the top end of the kovar base plate (15). Cold shield side grooves (28) are formed at the lower ends of the remaining two side faces of the cold shield (24). A detector lead (17) is provided outside the infrared detector (6), and the detector lead (17) is connected to a ceramic lead ring (18). A circular cold shield window (27) is formed at the top end of the cold shield (24) housing.

6. The integrated structure for cooling an infrared detector using a pulse tube refrigerator according to claim 4, characterized in that: Through-hole structures with thermometer sockets (33) running horizontally through the center positions are formed at both sides of the top end of the cold head (14). The columnar thermometer (25) is installed in the thermometer socket (33). The top end of the cold head (14) is provided with a cold head concave surface (32), and the kovar base plate (15) is arranged inside the cold head concave surface (32).

7. The integrated structure for cooling an infrared detector using a pulse tube refrigerator according to claim 4, wherein: The inner walls of the vacuum cover (43), the Dewar outer shell (42), and the outer surface of the cold shield (24) are all polished, and the inner surface of the cold shield (24) is blackened.

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