with two references ͓͑10͔ and ͓15͔͒ that were given incorrectly; as a result, in the online journal, the references did not link to the original articles.In Ref. ͓10͔ the journal citation should have read Phys. Rev. A 61, 044101 ͑2000͒; in Ref. ͓15͔, it should have read Phys. Rev. A 61, 063201 ͑2000͒. To enable the linking, the references have been corrected online as of 5 June 2003. The references remain incorrect in the print version of the article.

High-order harmonic generation from the interaction of high-intensity femtosecond laser pulses with the organic molecules benzene and cyclohexane has been observed using laser pulses of 240 and 70 fs duration at wavelengths around 800 nm. Harmonic intensities were measured as a function of laser intensity in the range 4ϫ10 13 -5ϫ10 15 W cm Ϫ2 , of laser polarization, and of the density of the medium. Harmonics from the 7th to the 13th order were found to have comparable intensities with those produced by xenon at the same density. The 7th harmonic from cyclohexane was measured to be four times more intense than that from xenon. No saturation of this harmonic was observed in cyclohexane up to a peak intensity of 2ϫ10 15 W cm Ϫ2 , in contrast with xenon, where saturation was seen above 8ϫ10 14 W cm Ϫ2 . These results are related to previous studies of ionization and fragmentation of these molecules in the same intensity range. The role of resonances between harmonics and high-lying molecular states is discussed.

We demonstrate efficient generation of high-order anti-Stokes Raman sidebands in a highly transient regime, using a pair of approximately 100-fs laser pulses tuned to Raman resonance with vibrational transitions in methane or hydrogen. The use of this technique looks promising for efficient subfemtosecond pulse generation.

We have investigated the behavior of high-order stimulated Raman scattering in a highly-transient regime. We demonstrate efficient collinear generation of vibrational sidebands in molecular hydrogen and methane using two-color pumping with pulses of duration ϳ 100 fs tuned to a vibrational Raman transition. A Raman spectrum with a large bandwidth was observed, ranging from the IR to the UV. Under some conditions strong pump depletion was observed and up to five anti-Stokes sidebands were observed to have energies exceeding 10% of the transmitted pump pulse energies. A numerical simulation reproduces qualitatively and quantitatively the experimental results and allows us to explain key experimental features. The simulation also confirms that the molecular coherence in the medium is substantially increased by the two-color pumping and allows us to deduce values for the degree of material excitation. The use of this technique looks promising for efficient subfemtosecond pulse generation.

We compare high-order harmonic generation in gas jets of benzene, cyclohexane, and xenon using ϳ800-nm laser pulses of 70 fs and 240 fs duration. The harmonic intensities of the 7th to 15th orders are studied as a function of laser intensity in the range 5ϫ10 13 to 5ϫ10 15 W cm Ϫ2. Using 240-fs pulses, the dependence of the harmonic intensity on the laser intensity of the organic molecules exhibits significant deviations from the behavior of atoms, and shows strong evidence for harmonic generation from molecular fragments as well as the parent molecule. When the pulse duration is reduced to 70 fs, the intensity dependences of the harmonics are similar to those of xenon. This is attributed to the significant reduction in dissociation occurring during the shorter pulse and suggests that high-order harmonic generation in the ultrafast regime will be important in the understanding of molecular electron dynamics in strong fields.