U.S. patent number RE31,279 [Application Number 06/091,121] was granted by the patent office on 1983-06-14 for laser optical resonator.
Invention is credited to James L. Hobart, Wayne S. Mefferd.
United States Patent |
RE31,279 |
Mefferd , et al. |
June 14, 1983 |
Laser optical resonator
Abstract
The reflectors in a laser are mounted in precise axial alignment
by means of an elongated mounting structure made of a material of
low thermal coefficient of expansion which serves to prevent
reflector misalignment due to temperature changes in the laser, the
elongated mounting structure also including an associated member
made of a material of high thermal conductivity which serves to
direct heat away from the elongated mounting structure along the
length, further reducing any temperature effects thereon. In
addition, a kinematic mounting structure is provided for further
enhancing the alignment stability characteristics of the plasma
tube and resonator structure.
Inventors: |
Mefferd; Wayne S. (Palo Alto,
CA), Hobart; James L. (Palo Alto, CA) |
Family
ID: |
26783614 |
Appl.
No.: |
06/091,121 |
Filed: |
November 5, 1979 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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842956 |
Jul 18, 1969 |
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Reissue of: |
292343 |
Sep 26, 1972 |
03783407 |
Jan 1, 1974 |
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Current U.S.
Class: |
372/107;
372/34 |
Current CPC
Class: |
H01S
3/086 (20130101); H01S 3/034 (20130101) |
Current International
Class: |
H01S
3/034 (20060101); H01S 3/086 (20060101); H01S
3/03 (20060101); H01S 003/02 () |
Field of
Search: |
;331/94.5G,94.5P,94.5C,94.5D,94.5T |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Petru et al., Structure and Technology of the Gas Molecular He-Ne
Light Generator, Jemma Mechanika A. Optica, 1964/2 (Jun. 12, 1963),
pp. 38-42. .
Strong, The Amateur Scientist, Scientific American (Sep. 1964), pp.
227 and 228. .
McManus et al., CO.sub.2 Laser Doppler Navigator Proves Feasible,
Laser Focus (May 1968), pp. 21-28..
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Primary Examiner: Sikes; William L.
Attorney, Agent or Firm: Wigert, Jr.; J. William
Parent Case Text
This is a continuation of application Ser. No. 842,956, filed July
18, 1969.Iadd., now abandoned.Iaddend..
Claims
What is claimed is:
1. A laser comprising an active lasing medium, means for creating a
population inversion in said lasing medium, an optical resonator
including a pair of reflectors aligned with each other and about
the active lasing medium to form the optical beam path of the laser
and for stimulating the emission of radiation along said path, a
pair of reflector adjustment plates in which said reflectors are
mounted, and means for accurately positioning and aligning said
reflectors including at least three spaced-apart rods made of a
material having a low thermal coefficient of expansion, the rods
extending parallel with but displaced from the optical path, the
outer ends of the rods being coupled to the reflector adjustment
plates, sleeves surrounding .[.at least a part of each of the rods
and.]. .Iadd.each of said rods over the entire length and said rods
are segmented and are coupled together by fixed bearings within
each sleeve and each sleeve .Iaddend.being made of a material of
high thermal conductivity for minimizing thermal gradients along
said rods, and means positioned along said rods for thermally
coupling by thermal conduction said sleeves for minimizing thermal
gradients both among and along said sleeves and said rods.
2. A laser as claimed in claim 1 wherein said sleeves are made of
aluminum.
3. A laser as claimed in claim 1 wherein said thermal coupling
means comprises a plurality of support members spaced-apart along
the laser supporting the plurality of sleeves.
4. A laser as claimed in claim 2 including a plurality of cradle
members associated with certain ones of said support members, said
cradle members serving to support said active lasing medium and to
equalize the temperature among the resonator rods.
5. A laser as claimed in claim .[.3.]. .Iadd.4 .Iaddend.including a
main base plate and flexure means for mounting said ones of said
support members on said main base plate.
6. In a laser including an elongated plasma tube and a magnet
solenoid surrounding and supporting the plasma tube, and wherein
the invention comprises an improved optical resonator comprising a
plurality of supports mounted in the laser and positioned in
longitudinally spaced-apart relationship along said magnet
solenoid, at least certain ones of said supports secured to said
magnet solenoid to support the plasma tube and magnet solenoid in
the laser, a plurality of sleeves made of a material of good
thermal conductivity extending beyond the two furthest apart
supports, a pair of resonator end plates, separate ones of the
resonator end plates being mounted on each end of the plurality of
sleeves, a reflector support plate movably mounted in longitudinal
alignment on each resonator end plate, each reflector support plate
having a reflector mounted thereon in axial alignment with the
plasma tube a, bearing member positioned within each sleeve at a
point between the ends of the sleeve, and a plurality of at least
three resonator rods made of material of low thermal coefficient of
expansion, one in each sleeve, extending from engagement at one end
against the bearing member outwardly through the sleeves to
engagement against the reflector support plates, said reflector
support plates including adjustment means at the point of contact
with the ends of the resonator rods for accurate alignment of the
relfector support plate and associated reflector with the plasma
tube and opposite reflector, and wherein said plurality of supports
are positioned between said .[.shields.]. .Iadd.sleeves
.Iaddend.and said solenoid for providing a thermal conduction path
between said sleeves for minimizing thermal gradients both along
and among said sleeves and rods. .[.7. A laser as claimed in claim
1 wherein each of said rods are segmented and are coupled
together by fixed bearings with each sleeve..]. 8. A laser as
claimed in
claim 2 wherein said rods are made of quartz. 9. A laser as in
claim 6 wherein each of said rods comprises at least two sections,
said sections being coupled together by bearing member positioned
within each sleeve at a point between the ends of the sleeve.
.[.10. In a laser including a lasing medium, an optical resonator
comprising a pair of reflectors, at least one reflector adjustment
plate in which a reflector is mounted, and wherein the improvement
comprises means for accurately positioning and aligning said
reflectors comprising a plurality of at least three spaced-apart
rods made of a material having a low thermal coefficient of
expansion, said rods extending parallel with and along the laser
optical beam path, the outer ends of the rods being coupled to the
reflector adjustment plate, sleeves surrounding each of the rods
and being made of a material having high thermal conductivity, and
means positioned along said rods for thermally coupling said
sleeves by providing a thermal conduction path therebetween for
minimizing thermal gradients both between and along
said rods..]. 11. A laser as in claim 1 wherein two of the planes
defined by the axes of said at least three parallel rods are
orthogonal to each
other. 12. A laser as in claim 6 wherein .Iadd.said plurality of
supports comprises three supports which are parallel to each other
and wherein .Iaddend.two of the planes defined by the axes of said
three parallel .[.resonator supportrods.]. .Iadd.supports
.Iaddend.are orthogonal to each
other. 13. An improved optical resonator for a laser for accurately
aligning and maintaining in alignment a pair of reflectors
comprising:
a. a base plate;
b. first means for preventing misalignment of said reflectors due
to temperature gradients across and along the optical resonator
comprising
i. a pair of reflector adjustment plates in which said reflectors
are mounted,
ii. three spaced-apart rods made of a material having a low thermal
coefficient of expansion, wherein the rods extend parallel with but
displaced from .[.the optical beam path of the laser.]. .Iadd.one
another .Iaddend.and the outer ends of the rods being coupled to
the reflector adjustment plates,
iii. sleeves surrounding .[.at least a part of each of the rods
and.]. .Iadd.each of said rods over the entire length and said rods
are segmented and are coupled together by fixed bearings within
each sleeve and each sleeve .Iaddend.being made of a material of
high thermal conductivity for minimizing thermal gradients along
said rods, and
iv. means positioned along said rods for thermally coupling by
thermal conduction said sleeves for minimizing thermal gradients
both among and along said sleeves and said rods; and
c. means for mounting said sleeves to said base plate, said
mounting means including second means for preventing misalignment
of said reflectors due to mechanical forces exerted on said base
during the operation of the
laser. 14. An improved optical resonator for a laser as in claim 13
wherein said thermal coupling means comprises a plurality of
support members spaced-apart along .[.the.]. .Iadd.a .Iaddend.laser
supporting the
plurality of sleeves. 15. An improved optical resonator for a laser
as in claim 14 including a plurality of cradle members associated
with certain ones of said support members, said cradle members
serving to support .[.the.]. .Iadd.an .Iaddend.active lasing medium
and to equalize the
temperature among said rods. 16. An improved optical resonator as
claim 15 wherein said second means comprises a first flexure means
for mounting said cradle members on said resonator support members
and second flexure
means for mounting said resonator support members on said base
plate. 17. An improved optical resonator as in claim 16 wherein two
of the planes defined by the axes of said .[.at least.]. three rods
are orthogonal to
each other. 18. An improved optical resonator as in claim 13
wherein two of the planes defined by the axis of said .[.at
least.]. three rods are orthogonal to each other.
Description
SUMMARY OF THE INVENTION
The present invention relates to a laser device and more
particularly to a novel mechanism for the precise mounting and
alignment of the plasma tube relative to the laser reflectors and,
in addition, a novel mechanism for mounting the complete laser
assembly on the main base structure.
In order to obtain optimum performance in the operation of a laser,
it is necessary that there be a precise angular alignment of the
resonator reflectors with the optical axis of the device. For
example, in a resonator comprising two facing and parallel flat
reflectors, it is necessary to establish and maintain the
reflectors mutually parallel to within one arc second. Misalignment
produces a decrease in the level of output stability, both
amplitude and frequency. In prior art devices, rigid unitary
structural members have been employed to mount the laser tube and
the two reflectors in precise axial alignment and, in addition,
detailed coarse and fine adjustment mechanisms have been utilized
to even more carefully produce such alignment in original
manufacture and subsequent field use. Although solid unitary
mounting structures may help to reduce misalignment due to
mechanical vibrations and the like, such a structure is extremely
sensitive to thermal changes during operation. For example, a
thermal gradient produced transversely to such an elongated
structural member will cause one side of the structure to change
its length slightly relative to the length of the other side. The
net effect will be a minute bending or curving of the elongated
mounting structure along its length which, while causing a slight
axial misalignment between the reflectors, more importantly causes
a canting of one or both of the reflectors and a movement away from
parallelism. A mechanical adjustment may be made to bring the
reflectors back into proper alignment, but the subsequent removal
or change in the value of the temperature gradient will result in
further misalignment.
In accordance with one embodiment of the present invention a novel
resonator mounting structure is utilized which comprises a
plurality of separate, spaced apart, elongated structural units
which, in their central region, carry the plasma tube and magnet
structure and, at their extremeties, carry the reflector mounting
and adjusting mechanisms. The mechanical arrangement of these
structural units in combination with the careful selection of the
materials used in the units is such as to substantially reduce the
chance of misalignment during operation of the laser. One element
of each of the structural units, the resonator rod which controls
the reflector alignment, is made of a material having a very low
coefficient of thermal expansion to reduce the effect of transverse
thermal gradients while another element of each of the structural
units, the resonator support tube which provides the major
structural support for the resonator, is made of a material of high
thermal conductivity to quickly dissipate heat from the support
structure during use thereby reducing the tendency for thermal
gradients to form in the support structure.
In this preferred embodiment of this novel structure, the plasma
tube and magnet assembly making up the main body of the laser is
held along the length upon a plurality of L-shaped support members
which are secured together in longitudinally spaced-apart and fixed
relationship by three hollow elongated resonator support tubes or
sleeves made of aluminum, a material of high thermal conductivity.
These sleeves extend beyond the L-shaped members and end plates are
fixedly secured on the ends of the hollow sleeves. Reflector
mounting and adjustment plates are moveable mounted by means of
flexible hinges or straps on the plates. Each adjustment plate is
adjustably aligned with the plasma tube and with the other
adjustment plate by adjustment screws, which engage the adjustment
plate and abut the ends of three elongated resonator rods extending
into the three resonator sleeves, the inner ends of the resonator
rods engaging a bearing member in each sleeve at approximately the
center portion of the sleeves. The reflector adjustment plates are
therefore, as far as the problem of alignment and positioning along
the optical axis is concerned, mounted on these resonator rods
which in turn are positioned from one central bearing or reference
point. The resonator rods are made of a material, for example,
quartz, having a low thermal expansion coefficient.
In addition to the problem of misalignment caused by thermal
gradients, lack of care in the mounting of the complete laser unit
on the users laboratory bench or the like may lead to misalignment
of the laser elements along the optical path.
The present invention provides a novel resonator support structure
to isolate to a degree the plasma tube, magnet structure and the
resonator structure from the main base of the laser so that
twisting or bending movements on the main base or laser casing will
not be translated into misalignment movements in the optical
system.
Other features and advantages of the invention will become apparent
from the following description of a laser structure embodying the
present invention taken in connection with the attached drawings in
which:
FIG. 1 is a perspective view partly broken away of a laser
structure which embodies the present invention;
FIG. 2 is a top view of one end portion of the laser structure;
FIG. 3 is a longitudinal cross-section view of one of the resonator
end plate structures of the laser taken along section line 3--3 of
FIG. 2;
FIG. 4 is an end view of the resonator plate structure taken along
section line 4--4 of FIG. 3;
FIG. 5 is a cross-section view through the laser device taken along
section line 5--5 of FIG. 1;
FIGS. 6 and 7 are longitudinal cross-section views showing the
structure utilized in mounting and adjusting the resonator plate
taken through section lines 6--6 and 7--7 of FIG. 4;
FIG. 8 is a longitudinal cross-section view of one of the two laser
mounting devices taken along section line 8--8 of FIG. 2;
FIG. 9 is a cross-section view of the mounting structure taken
along section line 9--9 in FIG. 8.
FIG. 10 is a top view, partially cut away, of the opposite end of
the laser structure from that shown in FIG. 2;
FIG. 11 is a cross-section view through one end of the laser taken
along section line 11--11 of FIG. 10;
FIG. 12 is a cross-section view through a portion of the resonator
plate adjusting mechanism taken along section line 12--12 of FIG.
11;
FIG. 13 is a longitudinal cross-section view of the other laser
mounting structure;
FIG. 14 is a cross-section of the mounting structure taken along
section line 14--14 in FIG. 13; and
FIG. 15 is a longitudinal cross-section view taken through the
center portion of one of the resonator sleeves as indicated by
section line 15--15 in FIG. 1.
Referring now to the drawings, the plasma tube 21 is mounted
coaxially within a hollow cylindrical magnet structure consisting
of the magnet tube or sleeve 22, (see FIG. 8), the solenoid 23
wound thereon, the magnet tube end members 24 affixed to the ends
of tube 22 and the annular tube supports 25 secured to the end
members 24 by means of screws 26. The plasma tube 21 is held within
the magnet at each end by means of O rings 27, retainer rings 28
and retainer caps 29 screwed onto the ends of the tube supports
25.
This plasma tube and magnet structure are mounted on the resonator
structure which in turn is mounted on the base plate 30 of the
laser at two longitudinally spaced points as shown in FIGS. 8, 9,
13 and 14.
With reference to FIGS. 13 and 14, a flexure mounting base 31 is
firmly secured to the base plate 30 by several screws (not shown).
A flexure plate 32 is secured to the base 31 by screws 33 and a
second flexure mounting member 34 is in turn secured to the flexure
plate 32 by screws 35 and is aligned with the lower base 31 by a
dowel pin 36 slidably extended into and between the flexure
mounting members 31 and 34. A crescent-shaped cradle 37 is fixedly
secured to the mounting member 34 by screws 38. The plasma tube and
magnet assemble including the magnet tube end member 24 rests in
the cradle 37 and is fixedly secured therein by means of a matching
crescent-shaped mounting clamp 39 bolted to the cradle 37 by scres
39'. A generally crescent-shaped flexible suspension plate 40 is
secured to the cradle 37 by two screws 41 located near the ends of
the suspension plate. The suspension plate 40 is also secured to an
L-shaped resonator support 42 by two screws 43 which are also
located near the ends of the plate 40. Location of the mounting
screws near the ends of plate 40 allow for greater flexibility
along the length of the plate.
The second mount, shown in FIGS. 8 and 9, includes a bearing mount
44 securely affixed to the base plate 30 by screws (not shown), the
mount 44 carrying a rotatable spherical bearing 45 thereon. A dowel
pin 46 slidably extends through the bearing 45, the end of the
dowel pin 46 being fixedly secured in a crescent-shaped support or
cradle 47. The magnet tube end member 24 rests in the cradle 47 and
is held therein by a mounting clamp 48. A crescent-shaped flexible
suspension plate 49 is secured near its ends to the cradle 47 by
means of two screws 50, the plate 49 also being secured to a second
L-shaped resonator support 51 by two screws 52. Again, this
flexible suspension member is free to flex over the major portion
of its length; the plate 49 is made of thinner metal than the plate
40 and is therefore more flexible.
The two L-shaped resonator supports 42 and 51 mounted on the two
suspension plates 40 and 49, respectively, form, along with a third
L-shaped resonator support 53, (see FIG. 5) the support for the
resonator assembly. These resonator supports each have openings
extending longitudinally through both ends and through their
corner, the three openings in each support being aligned with the
openings in the other supports. Three resonator support tubes or
sleeves 54 extend longitudinally through the aligned openings in
the three supports 42, 51 and 53 and are secured therein; for
example, with epoxy. The resonator supports and tubes are made of a
material having high thermal conductivity such as, for example,
aluminum which has a thermal conductivity of That is, if a plane is
drawn perpendicular to and intersecting the axis of each of the
resonator support sleeves 54 anywhere along their length, the
points of intersection of the support sleeves 54 and the plane
define a 90.degree. angle. Consequently, two of the three planes
defined by the axes of the support sleeves 54 form a right angle
whose junction is along the axis of the sleeve common to both
planes.
A bearing member 55 (see FIG. 15) is located in each of the three
resonator tubes at the position of the middle resonator support 53,
these bearings being secured in the tubes by means of set screws 56
extending through the support 53 and tubes 54. The outer ends of
the three resonator support tubes 54 are fixedly secured in front
and rear resonator end plates 57 and 58, respectively, which serve
to mount the laser mirror structures. A front mirror adjustment
plate 59 (see FIGS. 2, 3, 4, 6, and 7) is hung onto the front end
plate 57 by means of two flexure hinges or hangers 60 each secured
at one end to the end plate 57 by screws 61 and at their other ends
to the adjustment plate 59 by screws 62 (see FIGS. 4 and 6).
A hollow cylindrical mirror housing 63 is secured to the adjusting
plate 57 by cap screws 64. The transmission mirror 65 is positioned
axially within the housing 63 and is held therein by means of ball
bearings 66, rubber O ring 67, hollow cylindrical mirror holder 68,
and the retainer nut 69 which is threaded onto the end of the
housing 63.
A hollow cylindrical collet 70 (FIG. 3) is threaded into the mirror
adjustment plate 59 and extends axially through the end plate 57
toward the plasma tube 21. A hollow glass flange 71 extends over
the tubular end 72 and window 73 of the plasma tube 21 and into the
end of the collet 70 and is held in place by O rings 74 and
retainer caps or rings 75. The mirror mounting mechanism for the
rear end of the laser is similar and will not be described in
detail although the structural elements have been referenced on the
drawings with the same reference numbers as used to describe the
front end.
Three resonator rods 76 extend into the three resonator support
tubes 54 through the end plates 57 from each end of the laser, the
inner ends of the six rods having end plates 77 affixed thereto
(see FIG. 15) which bear against the bearing member 55 via chrome
moly balls 78. The resonator rods are of a material such as quartz
having a very low coefficient of expansion. Since the resonator
support tubes are maintained so that two of the planes formed by
them are in a 90.degree. relationship are explained previously, it
is apparent that the two of the planes defined by the three rods 76
likewise bear this orthogonal relationship. The outer ends of the
rods 76 each have an end plate 79 and an annular centering seat 80
firmly affixed thereto. The inner ends of three mirror adjustment
plate screws 81 contact the plates 79 at the outer end of each rod
76, the screws threadably engaging the adjustment plate 59. In
addition, two screws 82 and associated compression springs 83 also
serve to movably fasten the adjustment plate 59 to the end plate
57. At the rear end ofthe laser (see FIG. 12), spur and pinion gear
assemblies 84 are provided for two of the mirror plate adjustment
screws 81.
An elongated L-shaped resonator stiffener plate 85 extends the
length of the laser and is secured to the L-shaped supports 42, 51,
and 53 and the resonator end plates 57. Additional elements of the
laser not necessary to an understanding of the invention, such as
power transformers, cooling water tubing and ballast assembly have
not been shown. A cover or casing 86 encloses the laser.
Since the present invention is not concerned with the specifics of
lasering but rather the mounting and alignment structure and since
the details of lasering are so well known, no description of
lasering will be given here. The present invention is concerned
with establishing and maintaining the two mirrors or reflectors 65
in axial alignment with the plasma tube 21 and windows 73 and in
precise parallelism with each other for reasons well known to those
skilled in this art. Referring to the front end of the laser,
(FIGS. 3, 4, 6 and 7) the exact positioning of the reflector 65 is
controlled by the positioning of the reflector adjusting plate 59.
The plate 59 is mounted on resonator end plate 57 by means of the
straps 60 and screws 61 and 62, but the flexibility of this mount
permits relative movement between the reflector adjustment plate 59
and the end plate 57. The fixed positioning between these plates is
precisely determined by the three adjusting plate screws 81 and the
associated quartz resonator rods 76 which bear at their outer ends
against the screws 81 and at their inner ends against the bearing
member 55 located within sleeve 54 at the center position of the
laser. It can be seen, therefore, that substantially all the
structural members which serve to determine the axial alignment of
the reflectors over the entire longitudinal length of the laser are
made of a material, i.e., quartz, which is very little effected by
temperature changes in the laser during operation. In addition, the
rods 76 are independent of each other, except for the fact that
they contact the same mounting members at their end contact points,
and temperature-induced changes in one rod 76 will now necessarily
result in dependent changes in either of the other rods 76 to
compound the undesired misalignment effect. Also, the rods 76 are
surrounded over their entire length by sleeves 54 which are made of
a material having a high thermal conductivity and thus serve, along
with supports 42, 51 and 53 and resonator end plates 57, as heat
sinks, acting to isolate the rods 76 from temperature variations,
while acting together through their common supports 42, 51, 53 and
57 to prevent thermal gradients in the resonator support structure.
Once aligned, therefore, the two reflectors 65 will stay in
alignment during use over longer periods of time without attention
from the operator or the service engineer, resulting in enhanced
reliability and output stability, both amplitude and frequency.
Certain indirect benefits are obtained from this temperature
stability, for example a reduction in the water cooling capacity
needed, with a resultant reduction in water cooling structure and
over-all laser weight. Also, the greater independence from thermal
changes results in a reduction in the complexity of reflector
adjusting structures heretofore necessary. The reflectors in the
present laser may be easily and quickly removed and replaced and as
a result produce easy tunability and quick conversion from all-line
to single line operation.
In addition to the enhanced operation brough about by the reflector
mounting structure, the novel laser mounting structure shown in
FIGS. 8 and 13 provides even greater reliability and independence
from undesired mechanical forces exerted on the base or body of the
laser during operation. The resonator mounting including supports
42 and 51 is carried on the two cradle members 37 and 47,
respectively, via the flexible suspension plates 40 and 49. The
cradle members 37 and 47 are in turn carried on the base 30 via a
flexure plate 32 and the dowel pin 46 and spherical bearing 45,
respectively. The mechanical give provided by the flexibility of
plates 40, 49, and 32, the sliding movement of dowel pin 46 and the
rotational motion of bearing 45 insures that the entire resonator
structure will maintain a degree of independence from bending or
twisting motions of base 30. The plasma tube 21 and magnet assembly
22, 23 and 24 are all carried in the cradle members 37 and 47, held
there by clamps 39 and 48, and also benefit from the structural
flexibility of the cradle mounts.
While one specific embodiment of the invention has been illustrated
and described in detail herein, it is obvious that many
modifications thereof may be made without departing from the spirit
of the invention as described in the appended claims.
* * * * *