Diode-Array Side-Pumped Multiwatt Nd:YAG Laser

Abstract

The availability of ever more powerful laser diodes operating in the infrared or near visible spectral range led to an increased application of the diodes for pumping solid-state lasers. Diode pumping of solid-state lasers is performed either by end or side-pumping geometries. As well known, end or longitudinal pumping of Nd:YAG lasers is the method for obtaining higher conversion efficiencies of pump-to-TEM₀₀-laser outputs compared to side-pumped techniques /1/. As reported, in the more efficient end-pumped scheme for generating diffraction-limited output power, the pump light and the TEM₀₀ laser mode spatially overlap. However, end-pumped systems yielded lower output powers, while side-pumping seems easier scalable towards higher powers due to the larger lateral dimensions of the present diode laser arrays, and the simpler pump-light focusing optics. Optical conversion efficiencies of pump-to-Nd:YAG-laser output powers were reported to be approximately 30% when end-pumped, and 10% for side-pumped geometries /2/. It depends on what the diode-pumped laser system is finally used for, whether a high multimode output power or a fairly Gaussian mode profile is needed for a specific application. Therefore, considerable efforts are being made to improve both pumping schemes by using sophisticated imaging optics for focusing the pump light into the laser material. For example, a high power Nd:YAG laser achieved 1.9 W of TEM₀₀ mode output at 1.064 µm wavelength when end-pumped with a 10 W laser diode array /3/. Various geometries were studied using quasi longitudinal pumping techniques /4/. The authors have scaled the angular multiplex pump geometry to focus the power of eight 15 W laser arrays into the rod ends obtaining an optical-to-optical efficiency of 26%. The expected thermal distortion and stress-induced birefringence at these high pump power levels could be minimized.