Strong optical dipole force exerted on molecules having low rotational temperature

Abstract

We enhance the optical dipole force acting on molecules by decreasing the molecules’ rotational temperature and aligning the molecular axis with a linearly polarized nonresonant laser beam. The rotational temperature is decreased by increasing a source pressure from 2 to 81 bar. Using the effective polarizability directly pertaining to the optical dipole force, we evaluate the force and the resulting change in the velocity of the molecules. The theoretical calculations are compared with measurements based on the velocity map imaging technique. When the rotational temperature is reduced from 295 to 1 K, the maximum alignment is increased from < cos2 θ> = 0.33 to 0.92, the average optical force is enhanced by 74%.