Highly Efficient Organic THz Generator Pumped at Near‐Infrared: Quinolinium Single Crystals

A novel highly efficient ionic electro‐optic quinolinium single crystals for THz wave applications is reported. Acentric quinolinium derivatives, HMQ‐T (2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium 4‐methylbenzenesulfonate) and HMQ‐MBS (2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium 4‐methoxybenzenesulfonate) exhibit high order parameters cos 3 θ p = 0.92 and cos 3 θ p = 1.0, respectively, as well as a large macroscopic optical nonlinearity, which is in the range of the benchmark stilbazolium DAST ( N,N ‐dimethylamino‐ N ’‐methylstilbazolium 4‐methylbenzenesulfonate) and phenolic polyene OH1 (2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile) crystals. As‐grown unpolished bulk HMQ‐T crystals with a side length of about 6 mm and thickness of 0.56 mm exhibit 3.1 times higher THz generation efficiency than 0.37 mm thick OH1 crystals and about 8.4 times higher than 1 mm thick inorganic standard ZnTe crystals at the near‐infrared fundamental wavelength of 836 nm. Therefore, HMQ crystals with high order parameter obviously have a very high potential for high power THz‐wave generation and its applications.