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BaGa4Se7 is a new promising infrared nonlinear optical crystal. Recently, efforts are focused on the growth of high-quality single crystals. Single crystal with size of ϕ25 (diameter) × 35(length) mm3 was grown using vertical gradient freeze technique (VGF) for the first time. The yield of crack free crystals was greatly improved by selecting seed orientation for directional growth. Especially, the absorption coefficient of the BaGa4Se7 crystal is as low as 0.02 cm-1 at 2.05μm, which means that the as-grown crystal can be used to fabricate optical elements directly and does not need post-thermal annealing like other growth methods. The as-grown crystals were also characterized by X-ray diffraction (XRD), transmission spectra, and optical homogeneity etc. The BGSe-OPO elements were fabricated for infrared nonlinear optical experiments.

A GaSe: Al (0.13 wt%) single crystal was grown using the Bridgman method combined with a crucible rotation technique. A 35 × 19×5.5 mm 3 sample was cut from the as-grown crystal ingot. The GaSe: Al (0.13 wt%) crystal has an indentation hardness of 2.27 GPa, which is 2.6 times harder than the pure GaSe crystal. In particular, a sample with a thickness of 5.5 mm has an infrared transmission of approximately 60%. The absorption coefficient of this sample is as low as 0.1 cm −1 over the range of 0.83 to −14 μm, which demonstrates its high optical quality. A crystal growth method with the described procedures may be suitable to grow other doped GaSe crystals.

Recently developed chalcogenides nonlinear optical crystals have potential application in mid- to far-infrared laser fields. However, high-quality single crystals are hard to be prepared because of high vapor pressure of sulfur component and decomposition of chalcogenides during the polycrystalline synthesis and single-crystal growth. A pressure-assisted technique was performed to prepare stoichiometric AgGaS

High quality crystal AgGaGe5S12 (AGGSe), a promising infrared (IR) nonlinear optical (NLO) material, was grown using seed aided Bridgman Stockbarger technique with dimension size 30 mm in diameter and 60 mm in length. The crystal was characterized with X-ray diffraction, rocking curve, transmission spectrum and laser induced damage threshold (LIDT). The FWHM of the (2 1 0) peak is about 0.06° and the IR transmission is about 61% in an 2 mm thick sample, mean absorption 0.04–0.08 cm−1 in the range 0.95–15 μm. The surface LIDT was measured to be 220 MW/cm2, about triple the value of high quality AgGaS2 crystal with other experimental variable invariant. It may be good candidates for high-power NLO application.

High quality nonlinear infrared crystal material GaSe was grown using a seed aided Bridgman–Stockbarger method having a size of 24–26 mm in diameter and 55–70 mm in length. The crystals were characterized using X-ray diffraction, electron energy scattering, transmission spectrophotometry and infrared microscopy. The transmission spectrum showed that the infrared transmission is about 67% in an 8 mm thick sample cleaved along (001) face, and mean absorption 0.01–0.08 cm−1 in the range 0.9–15 μm. It may be suitable for the fabrication of infrared nonlinear optical devices, photoelectric analyzers of polarized light and so on. Crystals grown by this method with the described procedures may also be useful for other similar layered compounds.

ZnGeP 2 crystal is one of the most promising materials for infrared nonlinear optical applications. However, the near-band-edge absorption of native defects degrades the performance of ZGP-OPO device. The single-zone-annealing furnaces were utilized to anneal ZGP samples. The optimal annealing temperature was 600 °C and the optimal annealing atmosphere was ZGP powder vapor. For further annealing effects, the two-zone-annealing method was adopted to anneal ZGP crystals for the first time. The absorption coefficient can be reduced to 0.06 cm −1 at 2 μm and the resistivity can be increased from 5.8×10 7 Ω cm to 4.1×10 9 Ω cm. The results indicate that the annealed ZnGeP 2 crystals could be used as OPO devices. The mechanism of the two-zone-annealing effects has been briefly discussed in this paper.

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.

Single crystals of AgGaGeS4 (AGGS) were grown in a modified Bridgman furnace with 25 mm in diameter and 70mm in length. The transmission spectra of as-grown AGGS slices were measured on a Hitachi 270–30 spectrophotometer, the fabricated device crystal was 5 mm×5mm×3.5 mm in dimension and its absorption was 0.04–0.15 cm−1. Frequency doubling of 2.79 and 8 μm laser radiation were investigated using fabricated device crystals with thicknesses of 3.5 and 2.7 mm respectively.

We investigated the decomposition conditions of CdSe crystal with the aid of thermodynamics analysis. We chose the optimized growth parameters (1 MPa, 1250°C) based on the numerical simulation, and obtained single crystal boule with 28 mm in diameter and 70 mm in length. Preliminary tests showed that the crystal had fine homogeneity in composition (CdSe0.975), high infrared transmission (68-70%, 2.0-16 µm) and large laser induced damage threshold value (LIDT, 56 MW/cm2). This crystal may be a good candidate for the 8-12 µm mid-far nonlinear optical (NLO) material.

High quality nonlinear infrared crystal material AgGeGaS 4 with size 30 mm diameter and 80 mm length was grown via reaction of raw materials AgGaS 2 and GeS 2 directly. The as-prepared products were characterized with X-ray powder diffraction pattern and their optical properties were studied by spectroscopic transmittance. The absorption coefficient in the region of 6.8–7.8 μm is as low as 0.02 cm −1 , also, frequency doubling for 2.79, 8 μm with different lasers was demonstrated successfully. The reaction conditions are easy to be maintained and controlled, which may provide a new method to produce other high-quality Ag x Ga x Ge 1− x S 2 materials via changing the amount of GeS 2 .