High-order harmonic generation in cyclic organic molecules - art. no. 053810

High-order harmonic generation from the interaction of high-intensity femto second laser pulses with the organic molecules benzene and cyclohexane has been observed using laser pulses of 240 and 70 fs duration at wavelengths a round 800 nm. Harmonic intensities were measured as a function of laser int ensity in the range 4 x 10(13)-5 x 10(15) W cm(-2), 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 t he 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 2 x 10(15) W cm(-2), in contrast with xenon, where saturation was seen above 8 x 10(14) W cm(-2). T hese results are related to previous studies of ionization and fragmentatio n of these molecules in the same intensity range. The role of resonances be tween harmonics and high-lying molecular states is discussed.