Four-Color Stimulated Optical Forces for Atomic and Molecular Slowing

TL;DR

This paper explores four-color stimulated optical forces that significantly enhance atomic and molecular slowing, offering increased force magnitude and velocity range with reduced excited-state fraction, through numerical studies of bichromatic and polychromatic light fields.

Contribution

It introduces a four-color polychromatic force that improves force strength and velocity range while reducing excited-state population, advancing optical slowing techniques.

Findings

Force increased by nearly 50% with four-color scheme

Velocity range extended by a factor of three

Excited-state fraction reduced from 41% to 24%

Abstract

Stimulated optical forces offer a simple and efficient method for providing optical forces far in excess of the saturated radiative force. The bichromatic force, using a counterpropagating pair of two-color beams, has so far been the most effective of these stimulated forces for deflecting and slowing atomic beams. We have numerically studied the evolution of a two-level system under several different bichromatic and polychromatic light fields, while retaining the overall geometry of the bichromatic force. New insights are gained by studying the time-dependent trajectory of the Bloch vector, including a better understanding of the remarkable robustness of bi- and polychromatic forces with imbalanced beam intensities. We show that a four-color polychromatic force exhibits great promise. By adding new frequency components at the third harmonic of the original bichromatic detuning, the force is increased by nearly 50% and its velocity range is extended by a factor of three, while the required laser power is increased by only 33%. The excited-state fraction, crucial to possible application to molecules, is reduced from 41% to 24%. We also discuss some important differences between polychromatic forces and pulse trains from a high-repetition-rate laser.