Chiral specificity of doubly resonant sum-frequency generation in an anisotropic thin film

The chiral specificity of infrared-visible sum-frequency generation (SFG) is investigated under doubly resonant (DR) conditions. An anisotropic thin film made of stacks of chiral supramolecular assemblies is investigated as a function of incoming and outgoing, light polarizations. SFG experiments, crossed with in situ polarized absorption measurements, show that the double resonance process leads to a selection of the nonvanishing components of the chiral second-order susceptibility tensor. Specifically, it is demonstrated that a chiral component overcomes the achiral ones. This result is linked to the model for DR-SFG and to the selection rules of the vibration modes and electronic transition involved in the process.