Standing-wave effect in laser-saturation experiments or when 2 is less than 1

It is pointed out that, in order to obtain as large a population as possible in the upper state by laser pumping, the product of laser intensity and saturation parameter determines whether one gains or loses by reflecting the laser beam back into the saturated sample. Switching the polarization of the linearly polarized return beam by 90° eliminates this problem and is always advantageous.