High power laser employing an unstable resonator

DETAILED DESCRIPTION What is claimed is: 1.
In a high power laser: a positive branch unstable optical resonant cavity; a lasing gain medium positioned with said cavity and having a longitudinal axis for amplifying the intensity of a beam of coherent optical radiation passing therethrough along said longitudinal axis; means for pumping said lasing gain medium with sufficient energy to create a thermal gradient within said medium transverse to said axis which alters the medium's dielectric constant to form an optical lens having a characteristic focal length f; and said resonant cavity including first and second reflective means separated by such a distance and having respective focal lengths of such dimension, in conjunction with said optical lens, so as to cause optical energy within said cavity to be reflected back and forth between said reflective means and through said lasing gain medium over an optical path which is free of any focal points along said path in the region between said reflective means and so as to produce a substantial flow of optical power within said resonant cavity in a direction transverse to said optical path and said longitudinal axis.
2.
The laser of claim 1 wherein said optical resonant cavity, including the optical lens formed by the dielectric constant of the medium, is formed and arranged as a confocal optical resonator at a resonant optical wavelength of the cavity.
3.
The laser of claim 1 wherein the focal length f of the laser gain medium is determined by the equation f=2.
1/p where p is the average lamp input power in kilowatts and the focal length f is in meters.
4.
The laser of claim 3 wherein the laser medium is a yttrium aluminum garnet crystal doped with neodymium to less than one atomic weight percent.
5.
The laser of claim 4 wherein the neodymium doping is in the range of 0.
5 to 0.
8 percent by atomic weight.
6.
The laser of claim 1 wherein said first reflector means is a convex mirror disposed facing and coaxial with said second reflector means which comprises a concave mirror and including an output port disposed surrounding the periphery of said first reflector means