Picosecond relaxation measurements by polarization spectroscopy in condensed phases

A frequency domain technique is demonstrated which permits the determination of the homogeneous linewidth and relaxation rates of inhomogeneously broadened transitions in crystals, liquids, and glasses. The density-matrix formalism is employed to explain the origins of the intensity-dependent dichroism and birefringence observed in these experiments and to extract the relevant relaxation times. The samples initially studied were liquid solutions of the organic dyes malachite green and 1,3′ -diethyl-2,2′ quinolylthiacarbocyanine iodide. The ground-state recovery times were found to be 1.2±0.1 and 3.4±0.4 ps, respectively, for the two dyes in water solution. The transverse relaxation times were estimated to be less than 0.02 ps. The present technique is compared to resonant Rayleigh-type three-wave mixing and to time-resolved spectroscopic techniques.