Optical pump-terahertz probe spectroscopy of condensed phase reaction dynamics

The general theoretical and experimental principles of optical pump-THz probe spectroscopy of chemical reactions in liquids is presented. Background on specific difficulties encountered in the experimental observation is reviewed. Chiefly, signal-to-noise ratios currently limit the quality of information that can be extracted from optical pump-THz probe data on chemical reactions. This issue is shown to be connected to the assumption of linear response. The problem of interpretation of frequency dependent absorption coefficient data of neat liquids and solutions is addressed, and reasonably successful methods for analysis of the data are presented. Transient absorption coefficient spectra of < 111 > GaAs illustrates the type of information this spectroscopic method can extract from condensed phase samples.