A New Nonlinear Optical Selenide Crystal AgLiGa₂Se₄ with Good Comprehensive Performance in Mid‐Infrared Region

Mid‐infrared (mid‐IR) nonlinear optical (NLO) crystals are indispensable for the mid‐IR lasers generation with tunable wavelengths from 3 to 20 µm. AgGaSe 2 is a commercial mid‐IR NLO crystal with the highest figures of merit, but suffers low laser damage threshold (LDT). To achieve the balance of optical transmission, NLO effect, and LDT, it is proposed to molecularly modify the AgGaSe 2 structure by introducing the [LiSe 4 ] tetrahedra, and successfully grow large crystals of a new selenide AgLiGa 2 Se 4 . The replacement of half of the heavy Ag + cations with light Li + increases the band gap to 2.2 eV (vs. 1.7 eV in AgGaSe 2 ). The LDT value in AgLiGa 2 Se 4 increases five times compared to that in AgGaSe 2 , while keeping a relatively large NLO susceptibility of 26 pm V −1 . Moreover, the thermal expansion coefficients in AgLiGa 2 Se 4 are approximately two times lower in absolute value compared with AgGaSe 2 , which is beneficial to the large crystal growth. All these advantages would make AgLiGa 2 Se 4 a new promising NLO crystal for mid‐IR laser applications.