Spectral measurements of the emission from highly scattering gain media.

The spectral properties of the emission of a colloidal suspension of titanium dioxide particles in Rhodamine 640 perchlorate were studied systematically. The particle density rho, the dye concentration c, and the energy of the pump pulse were varied over several orders of magnitude; the dependence of the spectra on these three parameters is discussed. We discovered a strong correlation between the particle density and the dye concentration. The amplification by stimulated emission was found to be strongest when the absorption length l(a) and the mean-free-path length l(*) had approximately the same magnitude. The respective l(*) values were determined by a pulsed transmission experiment.