The effect of an antirelaxation coating on absorption in the $D_2$ lines of alkali metals

The specific features of absorption in a cell with an antirelaxation coating related to optical pumping and a finite rate of laser-frequency scanning are studied. The internal state of an atom in such cells is likely to remain unaltered after a collision with a wall. This results in optical pumping of an atomic ensemble over all velocities and the entire cell volume. Both the frequency corresponding to the maximum absorption in the $D_2$ line of $^{133}\mathrm{Cs}$ and the absorption maximum itself depend on the sign of laser-frequency scanning. A theoretical model attributing the power dependence of asymmetry of the absorption contour of the $^{133}\mathrm{Cs}$ $D_2$ line to the presence of cyclic transition levels in the system is presented.