Erratum: Multiphoton ionization of Na atoms in third-harmonic generation by a mode-locked Nd: YAG laser

Abstract

Effects of multiphoton ionization on third-harmonic generation in phase-matched Na and Xe mixtures have been investigated using a mode-locked Nd: YAG laser with a pulse duration of 28 psec and peak-power densities up to 3 \ifmmode\times\else\texttimes\fi{} ${10}^{12}$ W/${\mathrm{cm}}^{2}$. Analytical expressions accounting for refractive-index changes due to the depletion of neutral Na atoms and the plasma formation are presented which are used to estimate the wave-vector mismatch created by the multiphoton ionization of Na. The multiphoton-ionization probability $W$ for Na has been obtained from measurement of the number of ions formed by the focused laser beam: $W=6.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}49}{I}_{0}^{5}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ at $\ensuremath{\lambda}=1.064$ \ensuremath{\mu}m, where ${I}_{0}$ is the field intensity in W/${\mathrm{cm}}^{2}$. A time-dependent calculation using the value of $W$ obtained shows that multiphoton ionization of Na atoms brings about advancing and shortening of the third-harmonic pulse at high input intensities. The experimental results for the third-harmonic generation are in good agreement with calculated results which incorporated the effects of ionization. A comparison of the ionization effects with the quadratic Kerr effect is also presented.