Numerical model and study of cascaded third harmonic generation in two-sectioned a periodically poled Mg-doped LiTaO3 structure

The feasibility of cascaded second harmonic generation (SHG) and third harmonic generation (THG) in a monolithic two-sectioned periodically poled lithium tantalate crystal is analyzed. Simulation using a computational nonlinear optical model rigorously coupled with a thermal model suggests that 25%–30% THG efficiency can be achieved for a 3 W 20 ns pulsed 1.064 μm laser operating at 10 kHz if the crystal is composed of two sections: (i) ≈8.0 μm period first-order SHG structure and (ii) ≈6.6 μm period third-order THG structure. Significant inhibition of THG efficiency arises due to absorption of SH and TH, the heat release along the crystal, and associated thermal dephasing and lensing which can be effectively compensated by decreasing the temperature of the operating crystal below the quasiphase matching temperature. Corrections for the energy exchange lengths for optimal SHG and THG section design are suggested.