Laser-induced field-free alignment of the OCS molecule

14 Jun 2007

Researchers from Greece and France offer a detailed study of the field-free alignment of a polar molecule using short laser pulses (J. Phys. B: At. Mol. Opt. Phys. 40 2503).

The researchers describe the dynamical non-resonant alignment of jet-cooled OCS molecules using a short pump pulse with a duration of around 70 fs and an intensity of 10–20 TW cm⁻². The alignment of the molecules is determined by using a second weak laser pulse as a probe, and then analysing the orientational contribution of the optical Kerr effect.

The researchers observed that the maximum alignment possible is limited, since increasing the intensity of the laser pulse beyond a certain threshold results in ionization of the target molecules. However, they propose that optimizing the laser pulse should make it possible to increase the alignment beyond the limit imposed by ionization.

One possibility would be to use a single pulse with the intensity set below the saturation of ionization and tailor the pulse duration to maximize the alignment, while at the same time preserving the revivals of the wave packet. Other suggestions include employing a train of short pulses, or using a self-learning evolutionary algorithm to design more sophisticated pulses that would maximize the degree of alignment.