Direct measurements of collisionally broadened Raman linewidths of CO 2 S-branch transitions

Abstract

We report direct measurements of S-branch Raman-coherence lifetimes of CO2 resulting from CO2-CO2 and CO 2-N2 collisions by employing time-resolved picosecond coherent anti-Stokes Raman scattering spectroscopy. The S-branch (ΔJ = +2) transitions of CO2 with rotational quantum number J = 0-52 were simultaneously excited using a broadband (∼5 nm) laser pulse with a full-width-at-half-maximum duration of ∼115 ps. The coherence lifetimes of CO2 for a pressure range of 0.05-1 atm were measured directly by probing the rotational coherence with a nearly transform-limited, 90-ps-long laser pulse. These directly measured Raman-coherence lifetimes, when converted to collisional linewidth broadening coefficients, differ from the previously reported broadening coefficients extracted from frequency-domain rotational Raman and infrared-absorption spectra and from theoretical calculations by 7%-25%. © 2013 American Institute of Physics.