Long-Lasting Orientation of Symmetric-top Molecules Excited by Two-Color Femtosecond Pulses

Abstract

Impulsive orientation of symmetric-top molecules excited by two-color femtosecond pulses is considered. In addition to the well-known transient orientation appearing immediately after the pulse and then reemerging periodically due to quantum revivals, we report the phenomenon of field-free long-lasting orientation. Long-lasting means that the time averaged orientation remains non-zero until destroyed by other physical effects, e.g. intermolecular collisions. The effect is caused by the combined action of the field-polarizability and field-hyperpolarizability interactions. The dependence of degree of long-lasting orientation on temperature and pulse's parameters is considered. The effect can be measured by means of second (or higher-order) harmonic generation, and may be used to control the deflection of molecules traveling through inhomogeneous electrostatic fields.

Three Dimensional Orientation of Complex Molecules Excited by Two-Color Femtosecond Pulses

“…Despite the beats, the moving time average of this signal, like in the classical case, remains non-zero. Related effects of long-lasting orientation were analyzed and implemented using other orientation schemes [9,33,[38][39][40]46]. The existence of a non-zero time-averaged dipole signal relies on the combination of two factors: (i) the ability of symmetric/asymmetrictop molecules to precess about the conserved angular momentum vector and (ii) the symmetry breaking which is induced by the electromagnetic interaction.…”

“…Two-color pulses have been shown, both theoretically and experimentally, to be effective for orienting linear molecules [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. Recently, we theoretically considered the orientation of symmetrictop molecules excited by femtosecond two-color pulses [33], and previously experimentally demonstrated fieldfree 3D orientation induced by orthogonally polarized femtosecond two-color pulses [34].…”