Second harmonic generation in an optically active liquid: Experimental observation of a fourth-order optical nonlinearity due to molecular chirality

Abstract

Molecular left-right asymmetry is an origin of nonvanishing even-order optical nonlinear susceptibilities of nonracemic solutions of chiral molecules. Though second harmonic generation (SHG) due to quadratic dipolar nonlinearity is still symmetry forbidden in optically active liquids yet we have succeeded in experimental observation, for the first time, of noncollinear SHG due to a five-wave mixing process according to a scheme 2\ensuremath{\omega}=3\ensuremath{\omega}-\ensuremath{\omega}, governed by a fourth-order susceptibility tensor ${\mathrm{\ensuremath{\chi}}}^{(4)\mathit{D}}$. The SHG signal is found to be well collimated and quasi-phase-matched; it shows theoretically predicted polarization, intensity, spectral, and temporal properties.