Widely tunable and monochromatic terahertz difference frequency generation with organic crystal 2-(3-(4-hydroxystyryl)-5, 5-dime-thylcyclohex-2-enylidene) malononitrile

We report an experimental study on widely tunable terahertz (THz) wave difference frequency generation (DFG) with hydrogen-bonded crystals 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile (OH1). The organic crystals were pumped by a similar to 1.3 mu m double-pass KTiOPO4 optical parametric oscillator. A tuning range of 0.02-20 THz was achieved. OH1 crystals offer a long effective interaction length (also high output) for the generation below 3 THz, owing to the low absorption and favorable phase-matching. The highest energy of 507 nJ/ pulse was generated at 1.92 THz with a 1.89-mm-thick crystal. Comprehensive explanations were provided, on the basis of theoretical calculations. Cascading phenomenon during the DFG process was demonstrated. The photon conversion efficiency could reach 2.9%. (C) 2016 AIP Publishing LLC.