Phase sensitive detection of vibrational optical activity free-induction-decay: vibrational CD and ORD

Optical activity is manifested by chiral molecules including natural products and drugs, so that circular dichroism (CD) and optical rotatory dispersion (ORD) measurements can provide invaluable information on their chiro-optical properties and structures. It is experimentally demonstrated that heterodyne-detected Fourier-transform spectral interferometry with a femtosecond infrared pulse can be used to fully characterize the phase and amplitude of vibrational optical activity free-induction-decay field. The measured spectral interferograms are then converted to the linear optical activity susceptibility whose imaginary and real parts correspond to vibrational CD and ORD spectra. Unlike the conventional differential measurement technique, the present method based on a heterodyned interferometry is shown to be quite robust and stable. We anticipate that the present vibrational optical activity measurement technique will be of critical use in elucidating chiro-optical properties and structural changes in biomolecules.