Efficient third-harmonic generation with PPLN and PPLT

The focus of our work is to obtain efficient THG using cw or cw-like (i.e. cw mode-locked) laser sources. We have fabricated monolithic THG crystals (periodically poled lithium niobate and periodically poled lithium tantalate) with optimized designs for single THG interactions to obtain higher conversion efficiency. We achieved this using grating patterns with two different periods, arranged serially on the crystal, so that the first section performed SHG and the second section performed SFG. The primary difficulty of this approach is that both sections must phasematch at the same temperature. The published Sellmeier equations provide a starting point, but experimental iteration is required to obtain the correct pair of periods.