Japanese Journal of Applied Physics
Nonresonant Absorption of One Photon by One Atom and Resonant Absorption of Two Photons by Two Atoms
Masataka Mizushima
Abstract
When a radiation field of frequency ω1 interacts with atoms, etch of which has a transition frequency ω b a =(E b -E a )/\hbar, with ω1-ω b a =Δ≠0, nonresonant absorption can take place with probability P 1 inversely proportional to Δ 2 (a pressure broadening). When another radiation field of frequency ω2, such that ω1+ω2=2 ω b a , interacts simultaneously with the gas a resonant two-photon absorption can take place in addition to the nonresonant absorption. The probability of this two-photon absorption process, P 2, is found to be inversely proportional to Δ 4. If \varOmega=| <n-1|E|n ><b| µ|a >| is the Rabi frequency of the transition, it is found that P 2/(P 1(Δ)+P 1(-Δ)) is given by 12{ \varOmega(-Δ)\varOmega(-Δ)}2/{Δ 2(\varOmega(-Δ)2+\varOmega(Δ)2)}.