Laser-intensity effects in high-order autocorrelation calculations

The dependence of the higher-order harmonic generation signal produced by two time-delayed laser pulses on the delay between the two pulses has been studied with respect to the spatial laser-intensity distribution. The calculation is restricted to the laser-intensity dependence of the atomic response without taking into account coherence and/or propagation effects. It is found that the rapid modulations which the harmonic signal is expected to show in such a higher-order autocorrelation trace due to its nonmonotonic dependence on the laser intensity are totally eliminated after spatial integration over the laser-intensity distribution is performed. This study shows that the attosecond structures observed in experimental temporal traces of a superposition of higher harmonics produced by two delayed laser pulses cannot be attributed to laser-intensity-based artifacts, as recently suggested by Tempea et al. [Phys. Rev. Lett. 87, 109401 (2001)].