Non-linear optical spectroscopy as a novel probe for molecular chirality

Abstract

Optical second-harmonic generation and sum-frequency generation as novel spectroscopic tools to probe molecular chirality are currently being developed. The latter in particular allows studies of chirality associated with both electronic and vibrational transitions of molecules in isotropic bulk, thin films, and monolayers. We review here the recent theoretical and experimental progress in the field. It is shown theoretically and experimentally that both processes can have monolayer sensitivity to detect chirality in electronic and vibrational transitions and that the sensitivity of the sum-frequency spectroscopy of chirality in vibrational transitions can be greatly enhanced through vibrational-electronic double-resonance. Measurements with short-pulsed lasers provide opportunities for time-resolved in situ studies of chirality. Contents PAGE 1. Introduction 258 2. Basics of chiral responses in SFG and SHG 259 2.1. General considerations of SFG and SHG 259 2.2. Non-linear susceptibility for an azimuthally isotropic chiral surface 261 2.3. Non-linear susceptibility for isotropic chiral bulk 262 2.4. Normalization of non-linear susceptibility 263 3. Second-harmonic generation from chiral media 264 4. Chiral sum-frequency spectroscopy of electronic transitions 267 5. Chiral sum-frequency spectroscopy of vibrational transitions 281 6. Doubly resonant SFG 292 7. Conclusion 296 Acknowledgements 297 References 297