Determination of collisional line broadening coefficients with femtosecond time‐resolved CARS

The potential of femtosecond time‐resolved CARS for the determination of J‐dependent line broadening coefficients is demonstrated. With the well‐developed femtosecond technique the line broadening coefficients of the H2 Q‐branch ro‐vibrational transitions are measured in pure H2 and in H2 + He and H2 + N2 mixtures. The results for pure H2 show excellent agreement with the values obtained by other groups using high‐resolution CARS in the wavenumber domain. The dependence of the experimental broadening on perturber density also shows good agreement with the behavior of broadening found in the literature: a linear dependence in the case of hydrogen and helium as perturber and explicit non‐linear behavior in the case of nitrogen. The role of inhomogeneous broadening in time domain CARS is discussed.