Laser mirror alignment mechanism

A laser has a central axis, an outer envelope, a cathode end cap attached to the cathode end of the envelope, a cathode post attached at an inner end to the cathode end cap and extending axially therefrom generally coaxially along the central axis, and a laser mirror mounted to an outer end of the cathode post. An alignment mechanism is provided at the cathode end of the laser for aligning the mirror in a desired predetermined relation to the central axis. The alignment mechanism includes a cylindrical collar mounted to the cathode end cap in surrounding and outward radially spaced relation to the mirror-supporting cathode post, and a plurality of adjustment screws mounted to the collar at circumferentially spaced locations about the cathode post. The screws are independently movably adjustable in a radial direction relative to the laser axis toward and away from the cathode post for selectively applying deformation-inducing contact forces to the post directed transversely to the laser axis for causing angular deformation of the post relative to the laser axis to align the mirror mounted thereon in the desired predetermined relation to the axis.

BACKGROUND OF THE INVENTION 
The present invention generally relates to lasers and, more particularly, 
to a mechanism for adjustably aligning a laser mirror to its proper 
precise position for producing optimum lasing action. 
A conventional gas discharge laser, such as a helium-neon gas laser, 
typically includes an outer envelope which mounts components at its 
opposite ends defining an anode and a cathode. End mirrors are mounted 
adjacent opposite ends of the envelope by the anode and cathode 
components, and a bore tube is mounted within the envelope and in 
alignment with the end mirrors. To form an optical resonant cavity and 
produce optimum lasing action, the bore tube and end mirrors must be 
precisely aligned along a common, central axis. 
Adjustment of mirror alignment is made possible by the arrangement in which 
the mirrors are mounted at the ends of the laser envelope. For instance, 
with regard to the mounting arrangement of the cathode mirror in a typical 
laser construction, the cathode components include a cathode end cap 
attached to one end of the outer envelope of the laser and a cathode post 
electrically and mechanically connected thereto. The cathode end cap has a 
central opening and the cathode post is fixed at its inner end to the 
cathode end cap such that its central passage is coaxially aligned through 
the end cap opening with the central axis of the laser. The cathode mirror 
is mounted to the outer end of the cathode post, such as being adhesively 
bonded thereto, so as to extend generally perpendicular to the central 
axis of the laser. 
Generally speaking, alignment of the cathode mirror is typically carried 
out empirically by a technician during production of the laser. The laser 
is placed in a test fixture and activated to an operating state. The 
technician then manually adjusts the angular position of the mirror by 
bending the cathode post until the laser is operating in an acceptable 
fashion. 
Ordinarily, the technician bends the cathode post in one of two ways. The 
first way is a rather crude technique in which the cathode post is 
angularly deformed using a screwdriver. The second way is somewhat more 
refined. It uses a series of screws threaded into a plate attached to the 
inner end of the cathode post. The screws are threaded through holes in 
the plate so as to extend in generally parallel relation to the central 
axis and are pressed in contact against the cathode end cap. The 
technician threads selected ones of the screws toward the cathode end cap 
to cause the desired degree of tilting of the plate and cathode post and 
thereby the desired amount of angular adjustment of the cathode mirror 
with respect to the central axis. 
The above-described techniques are simply too crude and unrefined to 
provide the degree of control over the adjustment process necessary to 
achieve the level of precision in mirror alignment desired for optimum 
laser performance. Consequently, a need still remains for an improved 
approach to precise alignment of the laser mirrors. 
SUMMARY OF THE INVENTION 
The present invention provides a laser mirror alignment mechanism designed 
to satisfy the aforementioned needs. The mirror alignment mechanism of the 
present invention is useful in a laser having a central axis and a 
deformable mirror-supporting member mounted at an end of the laser and 
generally coaxially along the axis thereof. The alignment mechanism 
comprises: an annular member adapted to be mounted at the laser end in 
surrounding and outward radially spaced relation to the mirror-supporting 
member; and a plurality of adjustment elements mounted to the annular 
member at circumferentially spaced locations about the mirror-supporting 
member. The adjustment elements are independently movably adjustable in a 
radial direction relative to the laser axis toward and away from the 
mirror-supporting member for selectively applying deformation-inducing 
contact forces on the mirror-supporting member directed transversely to 
the laser axis for causing angular deformation of the mirror-supporting 
member relative to the laser axis to align the mirror mounted on the 
mirror-supporting member in a desired predetermined relation to the axis. 
More particularly, the annular member is in the form of a cylindrical 
collar which includes a base portion adapted to be attached to the laser 
end and having a central aperture adapted to receive the mirror-supporting 
member therethrough, and a cylindrical sidewall portion connected to the 
periphery of the base portion and extending therefrom. The sidewall 
portion of the collar has a plurality of circumferentially-spaced holes 
therethrough adapted to receive and mount the plurality of adjustment 
elements. 
Still further, the plurality of adjustment elements are in the form of a 
plurality of threaded screws mounted through the sidewall portion of the 
collar. The holes in the sidewall portion are threaded to receive and 
mount the threaded screws. 
Also, the mirror-supporting member of the alignment mechanism includes 
means defining a first weakened region in the form of a continuous groove 
in the member for permitting deformation thereof upon application of the 
deformation-inducing contact forces thereto by the selected ones of the 
adjustment elements. Further, another means defines a second weakened 
region in the form of another continuous groove in member for limiting 
transmission of the deformation-inducing contact forces applied thereon to 
a mirror mounted on an outer end of the member. The adjustment elements 
are movably adjustable for applying the deformation-inducing contact 
forces to the mirror-supporting member at circumferentially-spaced 
locations thereon between the first and second weakened region defining 
means thereof. 
Accordingly, it is an object of the present invention to provide a laser 
mirror alignment mechanism which provides a more mechanically and 
thermally stable way of precisely aligning a mirror with a central axis of 
a laser; to provide a mirror alignment mechanism which tends to make 
mirror alignment impervious to detuning through vibration and shock; to 
provide a mirror alignment mechanism which is cost-effective; and to 
provide a mirror alignment mechanism which allows more precise control and 
refined adjustment of the mirror position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference is made to FIGS. 1 and 2 of the drawings which illustrate an end 
portion of a laser 10, such as a gas discharge type laser. The laser 10 
employs a mirror alignment mechanism 12 which comprises a preferred 
embodiment of the present invention. 
In its basic components, the laser 10 includes an outer envelope 14 
providing a cavity 16 filled via a fill tube 18 with a gaseous mixture of 
helium and neon. An anode (not shown) and a cathode 20 are located at 
opposite ends of the envelope. Also, end mirrors 22 (only the one at the 
cathode end 24 of the envelope 14 being shown) are mounted adjacent 
respective ends of the outer envelope 14, and a bore tube (not shown) is 
mounted in coaxial relation with the envelope 14 within the cavity 16. To 
produce the desired lasing action, the bore tube and end mirrors 22 must 
be in precise alignment along a common central axis A of the laser 10. 
The cathode 20 is composed of several electrically connected components 
including a generally cylindrical cathode tube (not shown) which is 
disposed in the outer envelope 14 at the one cathode end 24 thereof, a 
cathode end cap 26 which is attached to the one end 24 of the envelope 14, 
and a cathode post 28 electrically and mechanically connected thereto. The 
cathode end cap 26 has a central opening 30 and the cathode post 28 is 
fixed at its inner end 32 to the cathode end cap 26 about its opening 30 
such that a central passage 34 through the cathode post 28 communicates 
with the opening 30 and is coaxially aligned with the central axis A of 
the laser 10. The cathode mirror 22 is mounted to an outer end 36 of the 
cathode post 28, such as by being adhesively bonded thereto, so as to 
extend generally perpendicular to the central axis A of the laser 10. 
Adjustment of the cathode mirror 22 into a precisely aligned perpendicular 
relationship with the central axis A to provide optimum operation of the 
laser 10 is made possible in an improved manner by the mirror alignment 
mechanism 12 of the present invention. Although the alignment mechanism 12 
is illustrated in conjunction with the cathode mirror 22, it may also be 
utilized with the anode mirror if desired. Therefore, it should be 
understood that the alignment mechanism 12 is not limited to use with the 
cathode mirror 22 at the cathode end 24 of the outer envelope 14. 
The mirror alignment mechanism 12 includes an annular alignment member 38 
mounted to the cathode end cap 26 in surrounding and outward radially 
spaced relation to the cathode post 28, and a plurality of adjustment 
elements 40 mounted to the annular member 38 at circumferentially spaced 
locations about the cathode post 28. The adjustment elements 40 are 
independently movably adjustable in a radial direction relative to the 
laser axis A toward and away from the cathode post 28 for selectively 
applying deformation-inducing contact forces on the cathode post directed 
transversely to the laser axis A for causing angular deformation of the 
cathode post 28 relative to the laser axis A to align the mirror 22 
mounted on the outer end 36 of the cathode post 28 in the desired 
perpendicular relation to the axis A. 
The annular alignment member 38 preferably is in the form of a cylindrical 
collar 38, for instance composed of stainless steel, which includes a base 
portion 42 attached to the cathode end cap, such as by epoxy or by being 
brazed thereto, and a cylindrical sidewall portion 44 connected to the 
periphery of the base portion 42 and extending axially therefrom. The base 
portion 42 of the collar 38 has a central aperture 46 sized to receive the 
cathode post 28 therethrough so that the collar 38 can be slipped over the 
cathode post 28 to install it on the cathode end cap 26. 
The continuous sidewall portion 44 of the alignment collar 38 has a 
plurality of circumferentially-spaced holes 48 defined therethrough being 
aligned in a plane extending transverse to the axis A of the laser 10. The 
holes 48 preferably are internally threaded, adapting them to receive and 
mount the adjustment elements 40, preferably in the form of externally 
threaded screws, so that they extend radially with respect to the axis A. 
Three screws 40 are illustrated in FIG. 2; however, four or more could be 
utilized if desired. 
For facilitating deformation of the cathode post 28 as is necessary to 
achieve the desired alignment of the cathode mirror 22 with the axis A, 
the cathode post 28 has means in the form of an outwardly-opening inner 
continuous groove 50 formed therein adjacent to the cathode end cap 26 and 
the base portion 42 of the alignment collar 38. The groove 50 defines a 
first continous annular weakened region 52 in cathode post 28 at the 
bottom of the groove 50. (A similar groove had been utilized heretofore in 
the prior art alignment arrangement discussed in the background section 
supra.) The groove 50 permits flexing and deformation of the cathode post 
adjacent to its attachment to the cathode end cap 26 and alignment collar 
38 upon application of the deformation-inducing contact forces thereto by 
manipulation of selected ones of the adjustment screws 40. 
The cathode post 28 also includes means in the form of an outwardly-opening 
outer continuous groove 54 formed therein spaced outwardly from the inner 
groove 50, remote from the cathode end cap 26 and the base portion 42, and 
adjacent to the outer end 36 of the post 28 and the mirror 22 mounted 
thereof. The groove 54 defines a second continuous annular weakened region 
56 in cathode post 28 at the bottom of the groove 54. The purpose of the 
groove 54 and second weakened region 56 in the cathode post 28 is to limit 
transmission of the distortion to the mirror 22 on the outer end 36 of the 
cathode post 28 to avoid sufficient stressing of the bond to cause 
breaking off of the mirror 22. As seen in FIG. 2, the adjustment screws 40 
are positioned to apply the deformation-inducing contact forces to the 
circumference of the cathode post 28 in the form of an annular land 58 
defined between the inner and outer grooves 50, 54 and first and second 
weakened regions 52, 56. 
The alignment mechanism 12 can actually be used in any one of several 
different approaches. In a first approach, all of the screws 40 are 
threadably adjusted to deform the cathode post 28 as required to align the 
mirror 22 in the proper relationship to the axis A. The screws 40 are then 
left in place. Another approach is to adjust the screws as in the first 
approach and then remove them from the collar 38. Since the post 28 has 
been deformed or bent to the desired extent, it will stay there and thus 
it is not necessary to leave the screws 40 mounted to the collar 38. A 
third approach is to install valier screws after the first set of screws 
40 are removed. The valier screws have a plunger arrangement which allow 
for achievement of a more fine adjustment than can be accomplished with 
the ordinary screws 40. 
Having thus described the laser mirror alignment mechanism of the present 
invention in detail and by reference to a preferred embodiment thereof, it 
will be apparent that modifications and variations are possible without 
departing from the scope of the invention defined in the appended claims.