Phase-matched optical harmonic generation in liquid media employing anomalous dispersion

A discussion is given of the conditions for production of a phase-matched optical third harmonic of a high-powered laser source by introduction of anomalous dispersion into a liquid medium. In particular, the role of the concentration of absorbers and their optical oscillator strength is discussed. In addition, experimental results previously reported by the authors for generation of the third harmonic of the neodymium laser line in the dye fuchsin red dissolved in hexaflueroacetone sesquihydrate (HS) have been extended for the same dye in another solvent, hexa-fluoroisopropanol (HI). In the latter solvent, phase-matched third harmonic generation is achieved at appreciably lower dye concentrations-37.5 g/l HI versus 45.0 g/l HS. The magnitude of the third harmonic signals generated at the phase-matched dye concentrations is approximately the same in both solvents, corresponding to about 0.2 mW for a laser power of 10 MW. A discussion of these findings is given in terms of the two physically important parameters that enter into the problem-the third order nonlinear susceptibility, and the optical attenuation at the third harmonic frequency.