Optimal Design of Mid-Infrared Nonlinear-Optical Crystals: From SrZnSnSe4 to SrZnSiSe4

Improving the laser damage threshold (LDT) of mid-infrared nonlinear-optical (MIR NLO) crystal materials is crucial for their applications in areas such as environmental monitoring and pharmaceutical detection. This paper presents the successful synthesis of SrZnSiSe4, a new MIR NLO crystal material that balances the LDT and second-harmonic-generation (SHG) effects and achieves phase matching. By replacement of Sn with Si in the existing SrZnSnSe4 material, the band gap of the material was increased, resulting in an LDT that is twice that of SrZnSnSe4, while maintaining the 2 × AgGaS2 effect. The SHG and band gap of SrZnSiSe4 derived from the experiments are 2 × AgGaS2 and 1.95 eV. The band gap of SrZnSiSe4 is better than that of SrZnSnSe4 (1.82 eV), and the LDT of SrZnSiSe4 is about twice that of SrZnSnSe4. Moreover, first-nature principal calculations confirm that SrZnSiSe4 can achieve phase matching after 1520 nm with a birefringence of 0.10, making it an excellent candidate for MIR NLO crystals.