We present the procedure for measuring self-phase modulation of ultrashort laser pulses focused in gases by use of the spectral phase interferometry for direct electric-field reconstruction (SPIDER) technique. We tested the device, which employs a noncollinear type I frequency mixing scheme, by measuring the phase induced by group-velocity dispersion either in a piece of glass or in the compressor of the laser system. Both results were validated by comparison with the expected values. The phase that resulted from self-phase modulation in H<sub>2</sub> gas or atmospheric air was then measured and compared with calculations based on a Gaussian beam assumption. A new estimate of the nonlinear index of refraction of H<sub>2</sub> at 800 nm was deduced. The data recorded in atmospheric air are in good agreement with the reported value of the nonlinear index measured with spectral methods.
© 2002 Optical Society of America
(120.3180) Instrumentation, measurement, and metrology : Interferometry
(120.5050) Instrumentation, measurement, and metrology : Phase measurement
(190.5940) Nonlinear optics : Self-action effects
(320.7100) Ultrafast optics : Ultrafast measurements
Shixiang Xu, Bruno Lavorel, Oliver Faucher, and Roland Chaux, "Characterization of self-phase modulated ultrashort optical pulses by spectral phase interferometry," J. Opt. Soc. Am. B 19, 165-168 (2002)