A diode laser mounted within a helium refrigerator is mounted using a braided copper ground strap which provides good impact shock isolation from the refrigerator cold-tip while also providing a good thermal link to the cold-tip. The diode mount also contains a rigid stand-off assembly consisting of alternate sections of nylon and copper which serve as cold stations to improve thermal isolation from the vaccum housing mounting structure. Included in the mount is a Pb-In alloy wafer inserted between the cold-tip and the diode to damp temperature fluctuations occurring at the cold-tip

Jennings, D. E.

English

NASA Technical Reports Server

United States Patent 1193 t113 4,161,747 
Jennings [45] Jul. 17, 1979 
[54] SHOCK ISOLATOR FOR OPERATING A 
REFRIGERATOR 
DIODE LASER ON A CLOSED-CYCLE 
[76] Inventors: Robert A. Frosh, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Donald E. Jennings, 
Berwyn Heights, Md. 
[21] Appl. No.: 880,838 
[22] Filed: Feb. 24, 1978 
[51] Int. C l . 2  ..................... HOlL 25/04, HOlL 23/02; 
HOlL 23/42 
[52] U.S. Cl. ........................................ 357/82; 357/83; 
357/74; 357/79; 357/81; 165/105 
[58] Field of Search ....................... 357/81, 82, 83, 79, 
357/74; 165/80, 105 
[561 References Cited . 
U.S. PATENT DOCUMENTS 
2,815,472 12/1957 Jackson et al. ........................ 357/82 
3,138,495 6/1964 Bylander et al. ...................... 357/83 
3,303,432 2/1967 Garfinkel et al. ...................... 357/82 
2,933,662 4/1960 Boyer et al. ........................... 357/82 
3,609,992 10/1971 Cacheux ................................. 357/83 
FOREIGN PATENT DOCUMENTS 
785461 10/1957 United Kingdom ...................... 357/83 
OTHER PUBLICATIONS 
IBM Technical Disclosure Bulletin, vol. 18, No. 4, pp. 
1226-1229, Sep. 1975, Close-Cycle Liquid Nitrogen 
Refrigeration System for Low-Temperature Computer 
Operation. 
Primary Examiner-Andrew J. Jslmes 
Attorney, Agent, or Firm-Robert D. Marchant; John R. 
Manning; John 0. Tresansky 
[571 ABSTRACT 
A diode laser mounted within a helium refrigerator is 
mounted using a braided copper ground strap which 
provides good impact shock isolation from the refriger- 
ator cold-tip while also providing a good thermal link to 
the cold-tip. The diode mount also contains a rigid 
stand-off assembly consisting of alternate sections of 
nylon and copper which serve as cold stations to im- 
prove thermal isolation from the vacuum housing 
mounting structure. Included in the mount is a Pb-In 
alloy wafer inserted between the cold-tip and the diode 
to damp temperature fluctuations occurring at the cold- 
tip. 
10 Claims, 2 Drawing Figures 
0 
/ 
0 
/ 
https://ntrs.nasa.gov/search.jsp?R=19790020378 2020-03-20T19:03:43+00:00Z
U.S. Patent Jui. 17, 1979 
. . - - . . - 
Sheet 1 of 2 4,16 1,747 
U.S. Patent Jui. 17, 1979 Sheet 2 of 2 4,16 1,747 
CLOSED 
-CYCLE 
REFRIG- 
101 
BENCH 
6 108 
INFRARED -g+, 
I RECORDER I 
4.16 1,747 
1 
SHOCK ISOLATOR FOR OPERATING A DIODE 
LASER ON A CLOSED-CYCLE REFRIGERATOR 
ORIGIN OF THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 
85-568(72 Stat. 434; 42 USC 2457). 
BRIEF SUMMARY OF THE INVENTION 
The invention relates to a structure for isolating 
shock and other vibration while maintaining a good 
thermal link. More particularly, this invention relates to 
mounting structure for a vibration sensitive component, 
such as a laser diode, which requires shock and other 
vibration isolation along with good thermal conduction 
through the mounting structure. 
Prior laser systems maintained their diodes at re- 
quired cryogenic temperatures by placing the diode 
within a liquid helium Dewar which did not present a 
vibration problem. However, this arrangement did have 
the disadvantage of requiring the Dewar to be fre- 
quently recycled to room temperature, which, in turn, 
had a adverse effect on the diode characteristic to the 
point where it would stop lasing. It also had the disad- 
vantage that the Dewar had to be periodically filled 
with helium which was both expensive and time con- 
suming. 
More recent laser systems use a closed-cycle helium 
refrigerator rigidly connecting the laser diode to the 
5 
10 
15 
20 
25 
30 
coldrtip of the- refrigerator thireby transmitting all of 
the vibrations of the refrigerator directly to the diode. 
These vibrations cause an instability in the diode output 35 
spectrum. Either the instability in the spectrum was not 
recognized or the instability was recognized but the 
source thereof was not understood. 
Accordingly, it is an object of the present invention 
to provide an improved mounting structure for a vibra- 40 
tion and temperature sensitive component. 
Another object is to provide an improved mounting 
structure capable of shock and other vibration isolation 
while providing good thermal conduction. 
A further object is to provide an improved mounting 45 
structure which damps temperature fluctuations from a 
refrigeration source. 
Yet another object is to provide an improved mount- 
ing structure having a improved thermal isolation capa- 
bility from its support. 
These and other objects of the invention are accom- 
plished by providing a highly flexible conductive strap 
between the temperature source and the component 
which is incapable of transmitting shock or other vibra- 
tions but is, at the same time, highly thermally conduc- 
tive. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a side view of the isolator of this invention 
supporting a laser diode in a closed-cycle refrigerated 
system. 
FIG. 2 is a block diagram of an infrared diode laser 
spectrometer used for gas analysis employing the isola- 
tor of this invention. 
DETAILED DESCRIPTION 
Referring to the drawing wherein identical reference 
numerals identify like parts, FIG. 1 depicts the rear end 
50 
55 
60 
65 
2 
of a vacuum housing 10, a radiation shield 20, a housing 
support 30, a window 40, a helium refrigerator cold-tip 
50, and a laser diode mounting structure 60 for a laser 
diode 61. the vacuum housing 10 is a stainless steel 
shroud which is box shaped at one end and may be of an 
approximately 2" dimension and tubular at the other 
end. Located within the housing is the radiation shield 
20 which is tubular and may be about 14" diameter. The 
radiation shield reduces the heat load due to radiation 
that would appear from the vacuum housing 10. The 
shield is composed of oxygen free high conductivity 
(OFHC) copper coated with nickel for increased reflec- 
tivity. It is coupled to the first stage of a helium refriger- 
ator (not shown) to establish a 50" K. temperature. The 
vacuum housing 10 is supported by support 30 which 
may be a pylon functioning as an optical bench support. 
At the top of the support is a plate 31 which may be 
formed of stainless steel. Four stainless steel screws 32 
and 33 (two not shown) may be used to rigidly fasten 
the vacuum housing 10 to the housing support 30 while 
an O-ring 34 provides a vacuum seal. The window 40 
completes the vacuum tight housing structure. It may 
be about 1" in diameter and about 3 mm thick. In this 
case the window passes infrared light through and 
therefore may be formed of zinc-selenide, germanuim 
or any other material transparent to infrared. 
The cold-tip 50 of the closed-cycle helium refrigera- 
tor (not shown) protrudes into the vacuum housing 
containing the laser diode mounting structure 60. The 
cold-tip is constructed of OFHC copper and is con- 
nected in a mechanically rigid, thermally conductive 
fashion to the second stage of the refrigerator. Its nor- 
mal minimum operating temperature is about 8"-10" K. 
Because the cold-tip is directly connected to the second 
stage of the refrigerator, it is subject to the shock im- 
pulses and other vibrations occurring in the refrigera- 
tor. The most severe shock is believed to occur with the 
impact delivered during the expansion phase of the 
Solvay cycle. The cold-tip terminates in a flange 51 
which aids the required mechanical coupling to the 
laser diode mounting structure 60. The mounting struc- 
ture is considered as including everything interposed 
between the cold-tip flange 51 and the stainless steel 
plate 31, all of which is within the vacuum housing 10 
and essentially within the radiation shield 20. The fun- 
damental requirement of the mounting structure is to 
allow the transmission of the cold-tip temperature to the 
semiconductor laser diode 61 without transmitting the 
vibration from the cold-tip 50. Other functions of the 
mounting structure are to smooth out the temperature 
variations of the cold-tip 50, which tend to cause diode 
frequency instability, and to thermally isolate diode 61 
from the housing support 30. 
A round lead-indium (Pb-In) alloy wafer 62, of, for 
example, about 14" in diameter, is mechanically secured 
to the cold tip flange 51 to function as a damper or 
thermal integrator smoothing out variations in the cold- 
tip 50 temperature which occur during the refrigeration 
cycle. A round OFHC copper washer 63 with a flange 
64 of about a 14'' diameter mechanically secures the 
Pb-In alloy wafer 62 to the cold-tip flange 51 along with 
three stainless steel bolts 65 (two not shown), an OFHC 
copper threaded rod 66 and a stainless steel nut 67. A 
thin indium washer 68 is placed on the other side of 
copper washer 63 to provide good thermal contact with 
the washer. 
A braided copper ground strap 69 is an essential part 
of the mounting structure because it provides good 
4,16 1,747 
3 4 
thermal conduction and vibration isolation. One side of shown). The two temperature steps, Le., 50" K. and lo" 
the ground strap is connected, as by soldering, directly IC., established by the cold-stations created at the cop- 
to an OFHC copper diode mount 71. The other side of per layers 75 and 79 serve to lower the thermal load 
the ground strap is in direct contact with the indium from assembly section to assembly section and create an 
washer 68 which also provides a good contact to the 5 effective thermal isolation between the diode mount 71 
ground strap because it is soft and highly conductive. and the housing support 30 as is required to keep the 
The ground strap 69, indium washer 68 and copper diode 61 at operative temperatures. 
washer 63 are mechanically fastened together by a bolt FIG. 2 depicts a typical infrared diode laser spec- 
70 such as a stainless steel Allen-head cap bolt. trometer 100 used to study various characteristics of 
The copper diode mount 71 provides a direct thermal 10 gases which employs the present invention, The spec- 
contact as well as one electrical contact to a substrate trometer includes the c~osed-cyc~e helium refrigerator 
contact to diode 61 is a wire to the other side of the piston second stage 103. A piece vacuum hose 
diode (not shown). The semiconductor laser diode 104 to decouple the vibration existing at the 
to monochro- Cold-tip 50 is at the end of the refrigerator second stage. 
Radiation shield 20 connects to the refrigerator first matic (single frequency) light in the infrared spectrum, 
stage. Pb-In alloy wafer 62 is next to the cold-tip. Also i.e., h=1-30 pm, e.g., h=9-11 pm (CW) when the crystal is held at cryogenic temperatures, Le., between 
about o" and K. The of the problem 2o included are the braided ground strap 69, laser diode 61, 
vibration. For stable operation, therefore, the diode the diode 61 Passes through lens 105 which is used to 
must be shock isolated while concurrently cooled at a collimate the light. The collimated light is Placed 
constant temperature. 25 through an absorption cell 107 containing a gas to be 
A stand-off assembly 73 rigidly attaches the diode analyzed. The emerging light is then Placed through 
mount 71 to the housing support 30. This attachment another lens 108 to focus the light on an infrared detec- 
must be done in a fashion that thermally isolates the tor 109 whose Output voltage is related to light inten- 
mount from the support, which is at room temperature. sity. During this operation the diode 61 is swept in 
Without thermal isolation there will be a thermal load 30 frequency by varying the current through it. The elec- 
on cold-tip 50 and diode mount 71 which will reduce tronics 110 accepts the voltage output from the infrared 
the mount temperature. The requirement for a mechani- detector 109, correlates it with the sweep in diode out- 
cally rigid structure without a substantial termal load is put wavelength and prepares the information in a form 
met by establishing two cold-stations in the stand-off suitable for a recorder 111, which may be a pen re- 
assembly as will be explained hereinafter. 35 corder which will produce a written record of light 
The standoff assembly 73 is formed of two layers of intensity versus wavelength. 
copper sandwiched between three layers of nylon The principles, preferred embodiment and mode of 
which serve as thermal insulators. A nylon layer 74 operation of the present invention have been described 
directly contacts an OFHC copper layer 75 which, in in the foregoing specification. The invention which is 
turn, is connected thermally to the cold-tip 50 via the 40 intended to be protected herein, however, is not to be 
copper threaded rod 66 and a piece of braided copper construed as limited to the particular form disclosed 
ground strap 76. This arrangement establishes a first since this is to be regarded as illustrative rather than 
cold station at about the cold-tip temperature Of about restrictive. Variations and changes may be made by 
lo" K. while also vibration isolating the standoff assem- those without departing from the spirit 
bly from the cold-tip. Copper layer 75 is disposed atop 45 of the present invention. 
another nylon layer 77 which is threaded at one end. 
layers 74 and 77 are coup1ed by a stantially constant temperature and substantially iso- 
threaded rod 78 extending therethrough. A double-end lated from vibration in a c~osed-cyc~e r frigerator, com- threaded OFHC copper layer 79 is fitted to the 50 prising: 
threaded end of nylon layer 77 through an opening 21 
formed in the radiation shield 20. A third threaded radiation shield within said housing for 
nylon layer 80 is fitted to the other threaded end of 
copper layer 79. The opposite end of nylon layer 80 fits 
screw 81, preferably formed of stainless steel, fits 
through a hole 36 formed throught plate 31 into another 
threaded of nylon layer 80 to complete the 
mechanically rigid assembly. A vacuum is maintained 
by O-ring 84. Another braided copper ground strap 82 60 
thermally connects copper layer 79 to radiation shield 
20 with a stainless steel screw 83 to establish the second 
cold station at about the radiation shield temperature of 
about 50" K. The ground strap 82 is usually clamped to 
copper layer 79 to allow for rotation. Ground strap 82 65 
also serves to isolate the assembly from vibrations car- 
ried by the radiation shield 20 due to its direct connec- 
tion to the first stage of the vibrating refrigerator (not 
contact 72 for laser diode 61* The Other electrical 181 with its large-piston first stage 102 driving its small- 
(SDL) 61 in this instance is a lead (pb outside ofthe refrigerator from the vacuum housing 10. diode which converts DC 
solved by this invention is that the output frequency of mounting structure window and housing 
the emitted light can also change with temperature or 30 placed on a bench 106. The infrared light output of 
in the 
What is claimed is: 
The diode mount 71, copper layer 75, and the nylon 1. Apparatus for maintaining a component at a sub- 
housing means; 
reducing radiaton heat from said housing means; 
shield means and coupled to a cold tip of said re- 
frigerator; and 
means for mounting said component within said radi- 
ation shield means, including; 
thermal contact means spaced from said thermal 
damper means for mounting said component 
thereon, 
flexible and thermally conductive strap means cou- 
pled between said thermal contact means and said 
thermal damper means for isolating said compo- 
nent from vibrations of said refrigerator and for 
thermally connecting said component to said cold 
into a 35 formed in stainless steel plate 31, A 55 damper surrounded by said radiation 
tip, 
4,16 1,747 
6 
first thermal insolator means connected to said ther- 
mal contact means for thermally insolating said 
component, 
thermal conduction means connected to said first 
thermal insolator means and flexibly and thermally 
coupled to said thermal damper means for isolating 
said component from vibrations of said refrigerator 
and for maintaining said thermal conduction means 
second thermal insulator means connected to said 
thermal conduction means for thermally insulating 
said thermal conduction means, 
another thermal conduction means connected to said 
second insulator means and flexibly and thermally 15 
coupled to said radiation shield means for isolating 
said component from vibrations of said radiation 
shield means and for maintaining said another ther- 
mal conduction means at substantially said radia- 
tion shield temperature, and 
third thermal insulator means connected to said an- 
other thermal conduction means for thermally in- 
sulating said another thermal conduction means. 
2. The apparatus of claim 1 wherein said flexible and 25 
5 
at substantially said cold tip temperature, 10 
20 
thermally conductive strap means is a braided copper 
ground strap. 
- 
3. The apparatus of claim 1 wherein said thermal 
4. The apparatus of claim 1 wherein said component 
5. The apparatus of claim 1 further including: 
thermal conduction washer means connected to said 
thermal damper means, and 
washer means connected between said thermal con- 
duction washer means and said flexible and ther- 
mally conductive strap means. 
6. The apparatus of claim 5 wherein said thermal 
conduction washer means is copper and said washer 
means is indium. 
7. The apparatus of claim 1 wherein said thermal 
conduction means is flexibly and thermally coupled to 
said thermal damper means by a braided copper ground 
strap. 
8. The apparatus of claim 1 wherein said another 
thermal conduction means is flexibly and thermally 
coupled to said radiation shield means by a briaded 
copper ground strap. 
9. The apparatus of claim 1 wherein said first, second, 
and third thermal insulator means are nylon. 
10. The apparatus of claim 1 wherein said thermal 
conduction means and said another thermal conduction 
means are copper. 
damper means is a lead indium alloy member. 
is a laser diode. 
* + + . +  
30 
35 
40 
45 
50 
55 
60 
65 


Shock isolator for operating a diode laser on a closed-cycle refrigerator

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server