Planar and annular waveguide lasers

Summary form only given. We review recent advances in the realisation of novel laser devices based on asymmetric laser gain geometries, which are made possible by new excitation techniques, Such lasers are characterised by waveguide propagation in one plane-the transverse direction for planar devices and radial direction for annular-coupled with waveguide, free space stable or free space unstable in the lateral/azimuthal direction. Two classes of large area waveguide laser are considered. In the first, the large area gain medium is produced by a transverse radiofrequency discharge excited gaseous gain medium. Using carbon dioxide as the active medium in a planar slab waveguide format, CW laser output power levels of several kilowatts have been achieved from a very small active volume where the gas is cooled by diffusion. High quality beams have been achieved from slab waveguide devices using either lateral 1-D unstable resonators or intra-cavity coherent imaging techniques in an all-waveguide configuration. The large area discharge concept has also been successfully applied to the carbon monoxide laser with emission in the 5.0 to 5.5 μm region and to the atomic xenon laser, where CW output power levels of several watts single line has been achieved for transitions at 2.0 to 3.5 μm. In the second class of planar waveguide laser, the gain material is a thin wafer of neodymium doped YAG or glass, and the optical pumping is achieved using a novel diode laser illuminator. The illuminator provides face pumping of the thin slab using a multipass arrangement which exploits the naturally high divergence of the diode laser pumps. Because the gain medium transverse dimensions are designed to accommodate low order mode optical waveguide propagation in that direction, in most cases the resonator design issue reduces to a 1-dimensional (lateral or azimuthal) design problem. The paper reviews a number of different hybrid waveguide/1-D resonator configurations which have been successfully employed with these asymmetric large area gain media to produce laser output beams which combine high output power extraction efficiency with laser beams of very high optical quality