Complete optical analysis of an UV laser dye using saturation techniques

The saturation properties of an UV laser dye, 3,5,3,5-tetra-t-butyl-p-sexiphenyl (TBS), pumped by a XeCl laser were studied. The experimental data included measurements of the optical saturation of transmission and amplifier gain. The data were fit directly to photon propagation differential equations to obtain the saturation intensities for absorption and emission. From the measured saturation parameters a complete determination was made of the optical constants of the singlet states in TBS. The results presented include the absorption spectrum, fluorescence spectrum, fluorescence lifetime, excitedstate absorption cross sections at the pump laser and dye laser wavelengths, quantum yield, wavelength dependence of the stimulated emission cross section, and an upper bound for the intersystem crossing rate. The saturation analysis method provides a rapid experimental evaluation of a laser dye with high accuracy. A two-photon excited transition at the long wavelengths of the laser oscillator tuning range of TBS produces photochemical degradation. The photochemical degradation rate increases with increasing wavelength.