Expansion and compression of the momentum distribution of atoms in the field of the counter-propagating frequency-modulated waves

We simulate the acceleration of atoms by the counter-propagating frequency-modulated (FM) waves. We show that the standard deviation of the velocity of atoms has a non-monotonic time dependence, and explain this phenomenon. The momentum diffusion coefficient of atoms in the field of FM waves is estimated from the analogy with the behaviour of atoms in the field of counter-propagating π\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\pi $$\end{document}-pulses. If the parameters of the atom–field interaction are optimal, the momentum diffusion coefficient linearly depends on light intensity. We obtain our results with the use of the Monte Carlo wave-function method and compare them with the results obtained by the solution of the optical Bloch equations. We compare our results with the behaviour of atoms in the field of the counter-propagating bichromatic waves.