We present spatially and spectrally resolved measurements of light emerging from the focus of an intense 25-fs laser pulse in gaseous media. The pulses are focused inside a chamber backfilled with either argon or air to nominal vacuum intensities of up to 5×10<sup>15</sup> W/cm<sup>2</sup>, far in excess of that necessary for ionization. We have recorded spectral-spatial maps for various pressures and pulse energies and have compared the results of argon and air. This survey is done in the regime where ~0.1% of the laser light is converted into the third harmonic, which is of practical importance since it is the largest conversion efficiency measured to date while maintaining such a short pulse duration. These measurements are, to our knowledge, the first of their type and are performed with a laser beam of very high spatial quality. The dynamics of an intense laser focusing into a gas cell is complicated, and these measurements provide a way to compare numerical simulations with an array of experimental information. The experiments also determine the conditions for optimal third-harmonic spatial beam quality in this regime.
© 1998 Optical Society of America
(190.2620) Nonlinear optics : Harmonic generation and mixing
(190.5530) Nonlinear optics : Pulse propagation and temporal solitons
(190.7110) Nonlinear optics : Ultrafast nonlinear optics
(320.7120) Ultrafast optics : Ultrafast phenomena
J. Peatross, S. Backus, J. Zhou, M. M. Murnane, and H. C. Kapteyn, "Spectral-spatial measurements of fundamental and third-harmonic light of intense 25-fs laser pulses focused in a gas cell," J. Opt. Soc. Am. B 15, 186-192 (1998)