A SnS : A Structural Incommensurate Modulation Exhibiting Strong Second-Harmonic Generation and a High Laser-Induced Damage Threshold (A=Ba, Sr).

Structural modulations have been recently found to cause some unusual physical properties, such as superconductivity or charge density waves; however, thus-induced nonlinear optical properties are rare. We report herein two unprecedented incommensurately modulated nonlinear optical sulfides exhibiting phase matching behavior, A SnS (A=Ba, Sr), with the (3+1)D superspace groups P2 2 2(00γ)00s or P2 (α0γ)0, featuring different modulations of the [Sn S ] belts. Remarkably, Ba SnS exhibits an excellent second harmonic generation (SHG) of 1.1 times that of the benchmark compound AgGaS at 1570 nm and a very large laser-induced damage threshold (LIDT) of 8×AgGaS . Theoretical studies revealed that the structural modulations increase the distortions of the Sn/S building units by about 44 or 25 % in A SnS (A=Ba, Sr), respectively, and enhance significantly the SHG compared with α-Ba SnSe without modulation. Besides, despite the smaller E , the A SnS samples exhibit higher LIDTs owing to their smaller thermal expansion anisotropies (Ba SnS  (1.51)