Fig. 1. Comparison between translational and rotational Doppler cooling and heating.
(A and B) Illustration of translational Doppler cooling. In the laboratory frame [(A), top], a particle is moving with velocity v in the presence of two counter-propagating light waves (wavy curves) of frequency ω. In the frame moving with the particle [(A), bottom], the extinction cross section (σext) of these two waves [see (B)] is affected by Doppler shifts to ω(1 ± v/c), leading to an optical force that pushes the particle to the left, thus causing particle deceleration in the laboratory frame. (C) We consider a particle rotating with angular velocity Ω and illuminated by linearly polarized light of frequency ω (top). The incident light can be decomposed into right circularly polarized (RCP) and left circularly polarized (LCP) components, which are Doppler-shifted to ω ∓ Ω in the frame rotating with the particle (bottom). Black circular arrows denote the directions of the electric field rotation on the plane perpendicular to the wave vector.