Conservation laws and laser cooling of atoms

TL;DR

This paper uses conservation laws to analyze laser cooling of two-level atoms, showing how the lowest kinetic energy depends on atomic parameters and unifying classical and quantum approaches.

Contribution

It presents a conservation law-based framework for laser cooling that is valid across all regimes of the linewidth to recoil energy ratio, unifying classical and quantum theories.

Findings

The minimum atomic kinetic energy approaches the recoil energy as linewidth tends to zero.

The approach is valid for any ratio of linewidth to recoil energy.

It recovers the semiclassical theory as a special case.

Abstract

The straightforward application of energy and linear momentum conservation to the absorption/emission of photons by atoms allows to establish the essential features of laser cooling of two levels atoms at low laser intensities. The lowest attainable average kinetic energy of the atoms depends on the ratio $\Gamma/E_R$ between the natural linewidth and the recoil energy and tends to $E_R$ as $\Gamma$ tends to zero. This treatment, as the quantum mechanical ones, is valid for any value of the ratio $\Gamma/E_R$ and contains the semiclassical theory of laser cooling as the limiting case in which $E_R\ll \Gamma$.