Improved Nonlinear Mixing for High Average Power, Near-UV Generation

For many ultraviolet applications, beta-barium borate (BBO) is the material of choice for harmonic generation due to the outstanding nonlinear properties, ultraviolet transparency, and mechanical robustness of the single crystals. Despite these attractive features, issues that limit the usefulness of BBO for ultraviolet generation include heating, due to Intensity Dependent Loss (IDL) and surface damage. IDL, which is known to be a significant problem at 266 nm and shorter wavelengths while relatively unimportant at 355 nm, will be characterized at an intermediate wavelength of 315 nm. Despite being grown at high temperatures, BBO is water soluble so that polished surfaces are difficult to AR coat for high power, laser damage resistance. Characteristically, damage occurs at the AR coated surface at a lower level than the bulk, which has a high threshold. Results of Phase I will identify the severity of IDL in the near ultraviolet in flux-grown BBO, identify factors that may affect this limitation, such as flux inclusions, and investigate the use of CLBO as an alternative non linear crystal. In addition, Phase I damage tests will determine optimal AR coating techniques for BBO-type crystals when used in these high power applications. Phase II work will optimize the non linear material properties and AR coating.