Third-harmonic generation of mode-locked Nd:glass laser pulses in phase-matched Rb-Xe mixtures

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Abstract
Third-harmonic generation in phase-matched Rb-Xe mixtures has been produced using 7- and 300-psec pulses of a mode-locked Nd:glass laser with peak powers up to 200 MW. Maximum energy conversion efficiencies of 2.8% have been achieved. A theoretical analysis is given which includes the transient excitations of the system and the linear and nonlinear susceptibilities up to seventh order in the perturbation. Agreement between theory and experiment has been obtained up to the highest input intensities demonstrating the importance of the transient excitation due to the adiabatic following. The phase-matching condition for parallel and focused beams has been investigated showing the influence of density gradients at the boundaries of the nonlinear medium (Rb vapor) and of the field-dependent changes of the refractive index at high input intensities. The limiting processes of self-focusing and multiphoton ionization are discussed.