Modeling of photoacoustic Raman spectroscopy

Photoacoustic Raman spectroscopy (PARS) is a technique used to identify chemical species mixed in a gas or liquid based on their pattern of vibrational energy levels. Raman spectroscopy differs from the more familiar absorption spectroscopy by using a nonlinear two-photon process that can be more sensitive to small differences in vibrational energy levels. Thus, it can detect defect sites in solid-state optical materials or low concentrations of chemical species in gases. The Raman scattering process generates acoustic pulses that can be detected with a microphone. In this talk, we present an overview of PARS and present a model of the production of these acoustic pulses from the energy deposited in the medium during the Raman scattering process. We will discuss the different types of PARS (cw, pulsed, and resonant) and their relative advantages. Finally, we describe an experimental platform that we plan to use for validating the model. [This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.]