A quantitative analysis of the three-photon resonant third-harmonic generation (THG) obtained in a zone of silence of a supersonic free jet of N2 is reported. In this absorbing molecular medium the resonant THG spectra exhibit unusual features. A theoretical model taking into account the fast and large variations of the nonlinear susceptibilities χ(3), the wave-vector mismatch ΔK, and the absorption coefficients α(3) near the three-photon resonance frequency is developed in order to calculate the harmonic power frequency dependence. It is shown that the harmonic power is sensitive to the phase-matching conditions, leading either to enhancement or depletion of the harmonic signal. The measured extreme-ultraviolet three-photon resonant THG spectra obtained with the b1Πu(υ′ = 6) state and recorded for different laser-nozzle distances are found to be in good agreement with the simulated spectra.
© 1992 Optical Society of AmericaFull Article | PDF Article
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