Vertical gradient freeze growth of ZnGeP2 crystals for nonlinear optical applications

ZnGeP2 crystal is the leader among nonlinear crystals for middle IR. Large sized Φ20×90 mm3 ZGP single crystals have been grown successfully by the vertical gradient freeze technique. The crystallinity and optical properties of as-grown crystals were measured by XRD and transmission spectra respectively. The thermal conductivity was tested using PPMS. The absorption coefficient can be reduced to 0.08 cm−1 at 2 μm by post-annealing. The fabricated devices were also utilized to demonstrate SHG and OPO experiments for nonlinear optical applications.

► Large sized ZGP single crystals have been grown successfully by the vertical gradient freeze technique. ► Annealing in ZnGeP2 powders for 400 h at 600 °C, the transmission increases by 29.6% at 2 μm. ► High power mid-IR laser is achieved by SHG and OPO using fabricated ZGP samples.