Intracavity cw difference frequency generation by mixing three photons and using Gaussian laser beams

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Abstract
The theory of Intracavity cw Difference Frequency Generation (I.D.F.G.) by a three-photon mixing using Gaussian laser beams has been studied assuming that the pump wave is either a Gaussian circular or elliptical focusing laser beam, with the non-linear crystal placed in the signal laser resonator. It is shown that the difference frequency generated power of the intracavity system is many times larger than that obtained by extracavity difference frequency generation operating under the same conditions. The general expression for the enhancement factor indicates that this increased power is due to the high field intensity of the signal wave within the cavity and to the parametric amplification effect. This factor becomes very large when either the pump power reaches a resonant value or when the signal laser operates close to the threshold. Numerical results have been obtained for I.D.F.G. based on either cw-ring dye or cw-YAG:Nd 3+ laser using a 90° phase matching LiNbO3-crystal and a critical phase matching LiIO3-crystal respectively. It is shown that cw-I.D.F.G. is a favourable method for producing an efficient source of I.R. radiation suitable for uses in high resolution spectroscopy