High-order harmonic generation in aligned molecules

We demonstrate alignment control in high density vapors of CS2, hexane, and N-2 (similar to 10(17) molecules cm(-3)) using the electric field of a 300 ps duration laser pulse. This was sufficient to study for the first time the molecular orientation dependence of high-order harmonic generation using a second, 70 fs duration laser pulse of intensity similar to5, x 10(14) W cm(-2). We were able to modulate and significantly enhance the harmonic intensity in aligned molecules compared to the randomly oriented case. Our results are consistent with the existence of an anisotropic dipole phase.