Picosecond optical Kerr ellipsometry determination of S1→Sn absorption spectra of xanthene dyes

The excited-state absorption of rhodamine and pyronin dyes in ethanol is studied. The nonlinear optical Kerr ellipsometry pump-probe technique permits an absolute measurement of the differential absorption cross-section spectrum in the visible and near-infrared ranges. Energies and oscilla tor strengths of S-1 --> S-n transitions are evaluated with linear absorption and stimulated emission taken into account. A biexciton state is revealed within the stimulated emission band. Its binding energy (40 to 110 meV) and oscillator strength (0.3 to 0.6) are determined. Possible laser, optical modulation and optical limiting applications of xanthene dyes are discussed.