Temperature-insensitive frequency conversion by thermally-induced phase mismatch compensation using a non-phase-matched crystal

A simple and versatile thermally-induced phase mismatch compensation method by three cascaded nonlinear crystals is proposed and experimentally demonstrated for temperature-insensitive frequency conversion. The middle crystal, which is not required to be phase matched, compensates the thermally-induced phase mismatch generated in the first crystal. Additionally, the dispersion of air, which causes a phase shift between fundamental and harmonic waves, is utilized to reduce the demand of length accuracy of the middle crystal. The temperature acceptance bandwidth of frequency conversion in the three cascaded crystals is about double that in a single long traditional crystal with the same interaction length.