Variable Curvature Optics for Lasers

This invention relates to variable curvature optics and more particularly to variable curvature optics for counteracting the thermal lensing effects in laser rods.

When a solid state laser is operated, the center of the rod thereof heats up more than the outer portions of the rod such that the ends of the rod acquire a curvature which is a function of the thermal gradient within the rod. This curvature of the rod at the ends thereof will decrease the area of rod over which the TEM.sub.oo mode output will occur. Therefore, the total laser output would require a mask to permit only the TEM.sub.oo mode portion of the beam to pass through into the environment. This course of action, of course, is very inefficient since only a small portion of the available output is used.

Another solution to the problem is to grind the laser rod ends or the H.R. mirror into a properly shaped lens to compensate for the distortions created by the thermal lensing effects. This type of correction is only satisfactory for one laser power setting. When the laser is to be operated over a range of power settings this compensation will not suffice.

Accordingly, it is an object of this invention to provide an improved laser.

It is another object of this invention to provide a laser having means therein for counteracting thermal lensing effects in laser rods.

It is a further object of this invention to provide a laser having variable control for counteracting the thermal lensing effects in laser rods.

Briefly, in one embodiment of the invention a laser is provided having an H.R. mirror therein and means for applying variable deformations to the mirror to counteract the distortion of the ends of the laser rod occasioned by thermal lensing effects therein.

The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a partial sectional view of a laser having apparatus therein for providing controlled structural deformations to counteract thermal lensing effects in the laser rod;

FIG. 2 is a drawing illustrating schematically the loads applied to the H.R. mirror of the laser of FIG. 1;

FIG. 3 is an alternate embodiment of the apparatus for providing structural controlled distortion to the laser of FIG. 1; and

FIG. 4 is a drawing illustrating schematically the loading effects of the apparatus of FIG. 3.

Referring now to FIG. 1 of the drawings, there is illustrated thereby a laser having means for providing controlled distortion of an optical surface therein to counteract the thermal lensing effects in the laser rod. The laser rod 10 is bounded by a pair of mirrors 12 and 14 one of which is highly reflective and which form a resonant cavity 16 therebetween. The laser rod 10 may be any type of solid crystalline rod, for example, neodymium yttrium aluminum garnet (Nd:YAG). Laser rod 10 is pumped by a pump lamp 18 of any suitable type.

Associated with mirror 12 is a device 20 for providing controlled distortion of the mirror to counteract the thermal lensing effects in the laser rod 10. Either or both mirrors may be distorted, however, there is apparently no advantage in deforming both mirrors. In this embodiment of the invention controlled distortion of mirror 12 is provided by arranging a slotted ring 22 about a holder 24 in which mirror 12 is mounted. Arranged relative to the slotted ring for cooperation therewith are a pair of nutlike members 26 and 28 having threads thereon for permitting mating between members 26 and 28. The members 26 and 28 have bevelled edges 30 and 32 for cooperating with bevelled edges 34 and 36 on the slotted ring 22. When the members 26 and 28 are rotated with respect to each other pressure is applied against the bevelled edges 34 and 36 of the slotted ring 22 to put an edge moment on the mirror 12 and thus, cause controlled distortion thereof. This edge moment is typically illustrated by the arrow 37 of FIG. 2.

By visually observing the beam emitted from the laser the user can adjust the members 26 and 28 to apply properly controlled distortion of mirror 12 so that the beam divergence will be minimized.

An alternate embodiment to that of FIG. 1 is illustrated in FIG. 3 wherein members 38 and 40 are rotated with respect to one another to apply an edge moment to mirror 12 as illustrated by arrows 39 and 41 of FIG. 4.

As an alternative or addition to the edge moment created by members 38 and 40 the space 42 may be evacuated via an orifice 44 to apply a load to mirror 12 typified by the arrows 46 of FIG. 4. O-rings 48 and 50 provide sealing for the unit.

Loading of mirror 12 may also be accomplished by applying pressure to space 42 via orifice 44 instead of evacuating same. The means illustrated for applying loads to the edge of a mirror or about the edge of a mirror are merely representative. Other mechanisms which are hydraulic, electromagnetic thermally operated, etc., may be used. Thus, it is to be understood that the embodiments shown are to be regarded as illustrative only, and that many variations and modifications may be made without departing from the principles of the invention herein disclosed and defined by the appended claims.