Comparison of numerical simulations with experimental results of the atmospheric self-focusing propagation of femtosecond laser pulses

Summary form only given. We present a direct comparison of experimental data with numerical simulations. The numerical model employed here solves the centrally symmetric nonlinear Schrodinger equation including the instantaneous Kerr nonlinearity and second order dispersion, similar to the work of Rothenberg (1992). Our expectation for this model is to capture the behavior of the initial temporal and spatial compression in the regime prior to that in which other effects such as ionization, optical shock and electron refraction become important, with the goal of inferring the magnitude of the nonlinearity and the second order dispersion coefficient of air. In general, the dispersion coefficient affects the temporal collapse and not the spatial profile, whereas the nonlinear coefficient affects both spatial and temporal collapse. In the experiment, we measured the spatial and temporal profile of an approximately 100-200 fs, 800 nm pulse at propagation distances of 5.3 and 11.3 m as a function of the laser pulse energy. The numerical results clearly produce the trend of the spatial and temporal compression of the pulse as the laser energy is increased. We have explored a broad range of values in the nonlinear and dispersion coefficient; the best fit for the spatial and temporal collapse is shown. Despite a systematic difference in the temporal pulse width that can be attributed to the assumed pulse shape in the autocorrelation deconvolution, the experimental trends at 5.3 m are best represented by using a nonlinear coefficient of 0.04-0.06 fs-/spl mu/m/sup 2/ /nJ and a dispersion coefficient of 0.034 fs/sup 2///spl mu/m.