The fluorescence quantum distributions E(X) and fluorescence quantum efficiencies qF of rhodamine 6G in methanol and in water are measured for various concentrations up to the solubility limit. The fluorescence spectra are separated in monomer and dimer (ground-state dimer and closely spaced pair) contributions. The stimulated emission cross sections for the monomers and the dimers are resolved.

The third order hyperpolarizability y 1 ( |j 1 (-to 3 ;co 1 ,co 1 ,co 1 ) of the rare gases He, Ne, Ar, Kr, Xe and of N 2 are determined by third harmonic generation involving picosecond light pulses of a Nd-glass laser. The results are compared with reported experimental and theoretical values.

An experimental arrangement is described for determining refractive indices of absorbing liquids and solids over a wide spectral range. Reflection and transmission measurements are carried out. Refractive indices of rhodamine 6G-methanol solutions around the Si absorption band are presented.

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Abstract. The third-order nonlinear susceptibilities x { xxxx ( -^ w i> w i> &>i) versus concentration are determined for rhodamine 6G, fuchsin, and methylene blue in methanol. Third-harmonic generation of a modelocked Nd-glass laser is applied. The real and imaginary part of the nonlinear susceptibility are measured. A resonance enhancement due to absorption bands is observed. Here we determine the dependence of third-order nonlinear susceptibilities xx 3 xxx ( -^3; co l9 co u co x ) on dye concentration for rhodamine 6G, fuchsin and methylene blue in methanol. The efficiency of conversion of picosecond light pulses of a mode-locked Ndglass laser to the third harmonic is measured. The nonlinear susceptibilities are deduced by comparison with calculations [7]. The absorption coefficients and refractive indices entering the calculations are separately measured [8,9]. The nonlinear susceptibilities comprise contributions from the solvent and the solute. The complex solute hyperpolarizabilities are determined and compared with the real solvent hyperpolarizability. The resonance enhancement is analyzed.