Better Material For IR Nonlinear Optics

Commercially available nonlinear crystals that transmit light in the infrared region are used in optics and photonics but tend to be easily damaged by laser light. Chinese researchers report a new IR nonlinear optical material with a laser damage threshold significantly higher than that of commercially available materials (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja412405u). Jingui Qin of Wuhan University and coworkers synthesized the new material, Rb₂CdBr₂I₂, by heating RbBr and CdI₂ in water and slowly evaporating the solvent. They obtained a crystal structure, which shows that the [CdBr₂I₂]²⁻ anions align themselves as distorted tetrahedrons with the iodine atoms on the same side of cadmium, resulting in a net polarization. The material transmits light over the wavelength range 0.37–14 μm, is thermally stable to 490 °C, and has a laser damage threshold of 190 MW per cm². This threshold is six times that of AgGaS₂, a commercially available IR nonlinear optical material. Rb₂CdBr₂I₂ has a calculated band gap of 3.35 eV, which is wider than that of other IR nonlinear optical materials and which may explain the high threshold for laser damage.