Non-linear optical crystal is an important photoelectric information functional material, which plays an increasingly important role in modern technologies such as frequency conversion, optical parametric oscillation, electro-optic modulation and communication. At present, laser pointer can produce visible and ultraviolet non-linear optical crystals, such as KTiOPO4 (KTP), LiB3O5 (LBO) and CsLiB6O10 (CLBO), which can basically meet practical applications.
In the infrared band, although there are relatively mature commercial crystals such as AgGaS2 and ZnGeP2, it is difficult to grow single crystals with high optical quality. At the same time, their low laser damage threshold and severe two-photon absorption limit their wide application. Therefore, exploring infrared nonlinear optical materials with excellent performance has become an important direction for optoelectronic functional materials.
The Key Laboratory of Special Environmental Functional Materials and Devices, Chinese Academy of Sciences, Institute of Physical and Chemical Technology, has devoted itself to the research of new infrared nonlinear optical crystals in recent years. After systematic research, researchers have discovered that M2LiVO4 (M = Rb, Cs) are two mid-infrared nonlinear optical crystal materials with excellent performance. Both compounds have a wide transmission range, a large nonlinear coefficient (4 × KDP for powder frequency doubling Rb2LiVO4 and 5 × KDP for Cs2LiVO4, and both are phase-matchable) and a strong red laser pointer damage threshold.
It is worth mentioning that these two compounds are compounds of the same composition melting, and it is relatively easy to grow large single crystals with high optical quality, which means that these two crystals have potential application value in the mid-infrared band. In addition, through first-principles calculations, researchers have found that in the structural motifs of these two compounds, the VO4 group is the main source of the frequency-doubling effect of these two compounds.