Abstract:
A refrigerated environment for multiple laser sources and/or sensors which provides the same thermal conditions in a single cold-cycle refrigerator for the sensors and sources. A mounting structure which comprises a cold-head assembly accomodating plural sensors or sources and positions them for radiation transfer with the ambient while they are held at consistent temperature relationships for efficient operation.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to laser systems, and more particularly, to a mounting structure which provides the ability to cool and operate multiple laser sources and/or laser sensors in a single refrigerated environment. 
     BACKGROUND OF THE INVENTION 
     Many solid state laser sources, or laser diodes, before they will emit the desired electromagnetic radiation, must be cooled to cryogenic temperatures while being excited to a lasing condition. Laser diodes are generally inefficient, however, and thus convert into laser radiation only a small portion of the excitation energy, releasing much of the remaining energy as heat. Moreover, the efficiency of laser diode devices decreases with an increase in temperature, and frequency of emission also changes with temperature. Similarly, laser sensors require cooled operating temperatures for optimal performance. 
     To remove heat and thus keep a laser source of sensor cooled to its preferred operating temperature, a closed-cycle cryogenic helium refrigerator is generally used. The refrigerator generally consists of a compressor, flexible high pressure gas transfer lines and a cold-head in which cooling actually takes place. The laser source or sensor is mounted on a heat conducting structure affixed in turn to a mounting station which is thermally coupled to a cold finger connected to the cryogenic refrigerator. The cold finger maintains low temperatures, in the 7°-10° K. range, from the mounting station and provides a heat sink to conduct heat from the helium refrigerator. A heater, which may be the source itself, is then connected to the mounting station to control it to the desired operating temperature for either a source or sensor. The entire structure is mounted within a housing to maintain the low temperature condition. A window is provided at the end of the housing so that the sensors or sources can receive or emit radiation from or to external instrumentation. 
     Cold-heads have previously only been able to cool a limited number of laser sources or sensors at one time. Cold-heads which can hold three laser detectors are known. Similarly, cold-heads which can hold four laser sources are known. 
     In addition, because sources and sensors generally operate at different temperatures, cold-heads have not permitted simultaneous mounting or operation of both laser sources and sensors. Instead, two separate cold-heads have been required, one for the laser source and another for the detector. 
     Because it takes approximately three hours to cool a cold-head mounting station to the desired temperature, the limitation in number and type of source and sensor devices which can be mounted thereto severely restricts the throughput of the number of detectors of sources which can be tested in a given period of time. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for cooled operation of multiple laser detectors and laser sources in a single closed-cycle refrigerator, correspondingly improving the throughput of testing of sensors and sources. In one embodiment, a cold-head assembly for sensors is disclosed which permits operation and testing of up to eight laser detectors. In another embodiment, a cold-head assembly is disclosed which permits the operation and testing of up to ten laser sources in a single cooling cycle. In a third embodiment, a cold-head assembly is disclosed which permits simultaneous cooled operation of both laser sources and sensors in a single closed cycle refrigerator. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The invention will be more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a cutaway view of a refrigerator unit having a cold-head assembly of the present invention; 
     FIG. 2 is a perspective view of a multiple laser source cold-head assembly source support of the present invention; 
     FIG. 3 is a perspective view of a multiple detector cold-head assembly detector support of the present invention; 
     FIG. 4 is an exploded view of a refrigerator housing window assembly for use in the unit of FIG. 1; 
     FIG. 5 is an end view of the refrigerator unit of FIG. 1 having an 8-detector cold-head assembly detector support of the present invention; and 
     FIGS. 6A and 6B are side and top perspective views, respectively, of a combined laser source and sensor cold-head sensor and source support assembly of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference now to the drawings, there are shown preferred embodiments for apparatus to provide a cold-head mounting structure for multiple laser sources and/or sensors in a cold-cycle refrigerator. With reference to FIG. 1, a cutaway view of a refrigerator unit having a cold-head assembly with a multiple laser source cold-head assembly source support of the present invention is shown. A vacuum housing 12 encloses a cold-shield 14. The cold-shield 14 in turn encloses a cold finger assembly 20 and a mounting station assembly 40. 
     Cold finger assembly 20 protrudes from the motor portion of a cryogenic refrigerator (not shown), and includes a cold finger 22 which is generally constructed of oxygen-free high conductivity copper and which is connected in a mechanically rigid, thermally conductive fashion to the refrigerator. Cold finger 22 terminates in a copper-indium sandwich flange 24 which acts as a thermal fluctuation damper. The refrigerator has two stages--a first 77° K. stage, and a second stage to which the cold finger 22 is connected and which has a normal minimum operating temperature of about 7° to 10° K. 
     The flange 24 is connected by means of a thermal strap 26 to the moutning station assembly 40. Thermal strap 26 is designed to provide good thermal conductivity between the flange 24 and the mounting station assembly 40 with minimal transmission of vibration. While thermal straps are known, a good thermal strap is shown in U.S. patent application No. 162,270, filed on Feb. 29 1988, and invented by the same inventor and assigned to the same assignee as named herein. 
     The mounting station assembly 40 includes an insulating stand-off assembly 44 which is attached to a mount 42 by means of nylon balls 45 and set screw 47. Stand-off assembly 44 is in turn connected to housing support 46, which is connected through the vacuum housing 12 and cold-shield 14 to a mounting base 48. 
     Within the stand-off assembly 44 is a copper plate 30, which is generaly gold-plated. This plate is connected to the 77° K. stage by a thermal braid (not shown). The cold shield 14 is also connected to the refrigerator&#39;s 77° K. stage. In this way, the transfer of room temperature heat to the mount 42 via stand-off assembly 44 and the vacuum housing 12 is impeded. 
     Because the size of mount 42 is limited by the cross-section of the cold-shield 14, mount 42 can hold only a limited number of sensors or laser sources. To permit simultaneous operation of more sensors or sources than can be placed on mount 42, a modified cold-head assembly support is attached to amount 42 by means of reference pins (not shown) to prevent rotation and tightening screws (also not shown). 
     With reference to FIGS. 1 and 2, a multiple laser source cold-head assembly source support 50 is shown. Source support 50 is T-shaped, with a first portion 52 and a perpendicular second portion 54. The source support 50 is made of oxygen-free high conductivity copper, which permits good thermal conductivity between the source support 50 and the mount 42. In the disclosed embodiment, ten laser diode sources 56 are affixed to source support 50 on its widened portion 54. 
     The cold-head assembly of the present invention can also be applied to detectors. In FIG. 3, a T-shaped multiple detector cold-head assembly detector support 80 is shown having a first portion 82 and a perpendicular second portion 84. Multiple laser sensors 86 are inserted into this cold-head assembly detector support, in holes perpendicularly placed along the length of portion 84. Cold-head assembly detector support 80 is designed so as to put the light receiving plane of the laser sensors 86 in the same plane as the light transmitting plane of the laser sources 56 of FIGS. 1 and 2. As will be shown below, this permits the use of the same cold-shield and housing assemblies for both laser sources and sensors. 
     Because cold-head assembly source and sensor supports 50 and 80, respectively, extend beyond the end of the standard vacuum housing 12 and cold shield 14 of FIG. 1, shown at 43, a modified refrigerator housing window assembly must be used incorporating a housing extension 57, a housing cap 58 and a cold shield extension 60, as shown in FIGS. 1, 4 and 5. Cold shield extension 60 is preferably made of the same material as the cold shield 14, and is in thermal and mechanical contact with the cold shield 14 at a boundary 62. With reference to FIG. 4, the cold shield extension 60 has a rectangular aperture 64 which aligns with the laser sources 56 or sensors 86 to permit the passage of light. Similarly, housing cap 58 has a window 66 made of quartz or other infrared transmitting material 68 and held in place by a window retainer 70. Housing cap 58 is connected to housing 12 by means of a housing extension ring 57. Cold shield stand-offs 69, shown in FIG. 1, are provided for mechanical alignment and improved thermal conductivity, and are connected to two cold shield cap rods 67 (only one shown). Rods 67 and stand-offs 69 are used for mechanical alignment and support as well as for thermal conductivity. 
     Finally, the present invention can be used to provide a cold-head extension for simultaneous operation of laser sources and sensors. With reference to FIGS. 6A and 6B, mount 42 is connected to the vacuum housing 12 and the housing support 46 by the insulating stand-off assembly 44. As previously described, a copper plate 30 is located in an intermediate portion of this stand-off assembly 44 and is thermally connected to the 77° K. first stage of the refrigerator. In this specific third embodiment of FIG. 6, plate 30 is extended horizontally beyond the stand-off assembly 44 and is then folded upwards at a right angle to create a mount 33 for two detectors 32. These detectors 32 are aimed out a side window 35, while four laser sources 56 can be mounted at a lower temperature on the cold-head sensor and source support assembly 37. The side window 35 allows light to pass through the housing cap 58A and cold-shield extension 60A, respectively, while the laser sources are aimed through a front window 66A. In this way, a single refrigerator environment permits simultaneous operation of both detectors and sources. 
     As is apparent from the present description, other modifications and alternative implementations will occur to those versed in the art without departing from the true spirit and scope of the invention. Accordingly, it is not intended to limit the invention to what has been particularly shown and described except as indicated in the appended claims.