Crystal growth, structure, and optical properties of new quaternary chalcogenide nonlinear optical crystal AgGaGeS4

Abstract

AgGaGeS4 is a new quaternary chalcogenide nonlinear optical crystal in application to converting a 1.064 μm Nd:YAG laser to 4–11 μm mid-IR output. It has been clearly demonstrated a high laser damage threshold, 50 MW cm−2 at 1.064 μm, which makes it a promising material for high-power and sustained laser frequency conversion. However, the preparation of the AgGaGeS4 single crystal has been perplexed by the complex multiple chemical reactions, high vapor pressure and large undercooling degree. In this work, a unique cooling process is used to modify the vapor transport with mechanical oscillation method for higher quality polycrystal. Besides, diverse ways have respectively addressed the pivotal issues of crystal growth process by the Bridgman method, such as the degree of supercooling, growth rate and control of decomposition at high temperature. Eventually, we have obtained the AgGaGeS4 crystal and the maximum size is Φ30 mm × 50 mm. In addition, the non-polarization Raman spectra were recorded at room temperature with a 532 nm laser beam excitation source. The main vibration frequencies present around 107, 323 and 355 cm−1, and the relationship between the structure and lattice vibrational properties is also discussed and analyzed in detail. The crystal performs a good homogeneity and high transparency in the 0.5–11.5 μm spectral range, especially the absorption coefficient of annealed AgGaGeS4 wafer that ranges from 0.01 cm−1 to 0.05 cm−1 in 0.9–10 μm after annealing, which illustrate it suitable for further optical experiments and the comprehensive applications. Besides, the band gap changes from 2.787 eV to 2.805 eV after annealing. At last, the surface damage threshold is about 103 MW·cm−2 which is two times more than report, and the body damage threshold is about 132 MW·cm−2.