On High-Efficiency Third-Harmonic Generation via Cascaded χ(2) Processes in Orientation-Patterned GaAs

We numerically investigate high-efficiency third-harmonic generation via cascaded χ(2) processes in orientation-patterned Gallium Arsenide waveguides comprising two quasi-phase-matched sections. The first section is phase-matched for second-harmonic generation (ω→2ω) and the second for sum-frequency generation (ω+2ω→3ω). Assuming a continuous-wave pump at λ=10.61μm, the structure converts the fundamental to the third harmonic at λ3ω≈3.54μm, within the atmospheric transmission window. By solving the coupled-wave equations, we optimize the number of domains in each section and estimate THG conversion efficiencies exceeding 90% at a pump intensity of ∼100MW/cm2 in a total crystal length ≈1.6cm. Using temperature-dependent parameters from the Sellmeier equations for GaAs, we also address thermal tuning of quasi-phase-matching over the range 22–300 °C and pinpoint robustness against fabrication tolerances of ±10 domains and ±2% in domain length. Our results indicate two-section orientation-patterned GaAs as a suitable platform for high-efficiency frequency tripling from mid-infrared.

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