Magic Crossing Points of Temperature Dependent Cascaded Frequency Conversions in Nonlinear Photonic Crystals

In this study, we investigated the temperature dependence of cascaded parametric generations in nonlinear photonic crystals based on 2D periodically poled LiTaO
₃
(2D-PPLT) of square lattice structure. After establishing simultaneous multi-groups of frequency conversion from optical parametric generation (OPG) [1], it was found that the interaction of the signal (Xs), the idler (λi) and the pump can further lead to several cascaded nonlinear processes such as SHG, SFG and DFG. The latter suggest existence of what can be called "magic" crossing points when mapping the nonlinear interactions vs temperature. We used a square lattice of 2D-PPLT with a period of 8.52μm and a filling factor of 38%. The crystal length was 2cm with a thickness of 0.5mm and pumped with a pulse 532nm green laser with a peak power of 80kW and a pulse width of 0.5ns. The measured spectra of the cascaded frequency conversion processes reveal 10 wavelength peaks at 393nm, 402nm, 518nm, 532nm, 548nm, 787nm, 820nm, 1518nm, 1576nm and 1642nm at a crystal temperature of T= 110°C.