Fine-tuning molecular energy levels by nonresonant laser pulses

TL;DR

This paper investigates how nonresonant laser pulses can shift vibrational and rotational energy levels in molecules, enabling fine-tuning of molecular states and potential dissociation, with implications for spectroscopic control.

Contribution

It provides a detailed analysis of vibrational and rotational energy shifts induced by nonresonant laser fields, including both adiabatic and nonadiabatic interactions, applied to the 87Rb_2 molecule.

Findings

Adiabatic fields cause negative rotational shifts exceeding vibrational shifts.

Nonadiabatic pulses of specific durations induce comparable vibrational and rotational shifts.

Laser pulses of certain intensities can dissociate molecules or fine-tune rovibrational levels.

Abstract

We evaluate the shifts imparted to vibrational and rotational levels of a linear molecule by a nonresonant laser field at intensities of up to 10^12 W/cm^2. Both types of shift are found to be either positive or negative, depending on the initial rotational state acted upon by the field. An adiabatic field-molecule interaction imparts a rotational energy shift which is negative and exceeds the concomitant positive vibrational shift by a few orders of magnitude. The rovibrational states are thus pushed downward in such a field. A nonresonant pulsed laser field that interacts nonadiabatically with the molecule is found to impart rotational and vibrational shifts of the same order of magnitude. The nonadiabatic energy transfer occurs most readily at a pulse duration which amounts to about a tenth of the molecule's rotational period, and vanishes when the sudden regime is attained for shorter pulses. We applied our treatment to the much studied 87Rb_2 molecule in the last bound vibrational levels of its lowest singlet and triplet electronic states. Our calculations indicate that 15 ns and 1.5 ns laser pulses of an intensity in excess of 5x10^9 W/cm^2 are capable of dissociating the molecule due to the vibrational shift. Lesser shifts can be used to fine tune the rovibrational levels and thereby to affect collisional resonances by the nonresonant light. The energy shifts may be discernible spectroscopically, at a 10 MHz resolution.