New materials for non-linear optics based on hyperpolarizable molecules
Inorganic crystals such as KDP are often used in optoelectronic devices to double the frequency of a laser beam (SHG: second harmonic generation), thus enabling a much higher bandwith to be used in, eg., high-speed fiber-optics networks. Inorganic crystals are stable under very intense light, but their second-order nonlinear optical (NLO) properties are not as large as those exhibited by some organic molecules with large, easily polarisable, pi-electron clouds.
Charge transfer effects between a donor and acceptor group of a dipolar molecule enhance the polarisability, but these molecules tend to crystalise in
centrosymmetric structures that forbid bulk SHG. This problem can be avoided by co-crystalising the organic molecule with another (chiral) organic or inorganic species.
CEMDRX has an on-going research project in collaboration with Centre for Computational Physics of FCTUC aiming at engineering new non-centrosymmetric NLO crystals based on such octupolar moleculesm, such as TPG (Triphenylguanidine).
