Efficient Third-Harmonic-Generation Laser Sources

Third-harmonic generation (THG) of cw-diode-pumped solid-state lasers can be used to reach important wavelengths in the visible and ultraviolet. Because THG is implemented with two cascaded processes of second-harmonic generation (SGH) and sum-frequency generation (SFG) and the peak power of cw-diode-pumped solid-state lasers is low, efficient THG is difficult with conventional nonlinear materials. The emerging technology of periodic poling provides high nonlinearity and no walk-off so large nonlinear drive can be attained even with relatively low-peak-power lasers. Using the flexible design properties possible in periodically poled materials, a monolithic crystal can be fabricated that combines both the SHG and SFG processes in a single crystal. This has the advantage of reducing the number of surfaces which lowers the loss. By placing a crystal of this type in a resonant cavity, efficient THG of cw-diode-pumped solid-state lasers is made practical.This Phase I research will demonstrate a monolithic THG crystal using periodically poled lithium niobate (PPLN) and efficient THG of a cw-diode-pumped Nd:YAG laser. In addition, we will investigate low-absorption material which will enhance the conversion efficiency and power handling of THG devices. We will characterize the absorption of different samples of congruent and stoichiometric lithium niobate, and investigate the suitability of these materials for periodic poling.