By numerically solving the nonlinear field equations, we simulate second-harmonic generation by laser pulses within a nonlinear medium without making the usual slowly-varying-amplitude approximation, an approximation which may fail when laser pulses of moderate intensity or ultrashort duration are used to drive a nonlinear process. Under these conditions we show that a backward-traveling, second-harmonic wave is created, and that the magnitude of this wave is indicative of the breakdown of the slowly-varying-amplitude approximation. Conditions necessary for experimental detection of this wave are discussed.
© 2003 Optical Society of America
J. Z. Sanborn, C. Hellings, T. D. Donnelly, "Breakdown of the slowly varying amplitude approximation: generation of backward traveling second harmonic light," J. Opt. Soc. A. B, 20, 152-157 (2003). doi: 10.1364/JOSAB.20.000152