High-order harmonic generation in argon by elliptically polarized picosecond dye laser pulses

High-order harmonic generation is observed in an argon jet using elliptically polarized picosecond dye laser pulses. The experimental data appear to be in near agreement with the perturbation theory. However, there is a general trend of small deviation from the theory. We speculate that such a deviation could be due to the laser induced coupling of upper states in or near the continuum which relaxes the selection rules leading to an enhancement of harmonic emission.