A beam of light of frequency w, equal to the resonant frequency of transition of atoms of

Question:

A beam of light of frequency w, equal to the resonant frequency of transition of atoms of gas, passes through that gas heated to temperature T. In this case hw >> kT. Taking into account induced radiation, demonstrate that the absorption coefficient of the gas × varies as × = ×o (1 – e–hw/kt), where ×o is the absorption coefficient for T → 0.