Recent developments in transparent organics for second- and third-order nonlinear optics

Organic materials have been a focus of new nonlinear optical (NLO) materials development efforts in the late 1980s and early 1990s as a result of their often large second and third order optical nonlinearities and inherent chemical design flexibility. However, implementation of single crystal organic materials in practical device applications has been impeded by their often inadequate transparency, poor optical quality, lack of robustness, low laser damage threshold, and inability to grow in large-size crystals. The molecules in pure organic crystals are often coupled only by relatively weak van der Waals forces or hydrogen bonding which results in mediocre mechanical properties. Even for very promising and well characterized organic second harmonic generation (SHG) materials, large scale growth is often difficult, and quality can be compromised due to solvent impurity incorporation during crystallization.