Excitation of transitions between atomic or molecular energy levels by monochromatic laser radiation - I. Excitation under conditions of strictly homogeneous line broadening

Abstract

The development with time of the excitation of a transition between two atomic or molecular energy levels under the influence of monochromatic laser radiation is examined under conditions of strictly homogeneous line-broadening. The ratio of the number of atoms or molecules, N 2 , in an excited state to the total number, N , is calculated for various ratios of the intensity parameter β ═ E 0 μ/ ħ to the half line-width γ . E 0 is the amplitude of the electric field in the incident radiation and the dipole moment matrix element for the transition. Exact expressions for N 2 / N as a function of time are given for the situation when the frequency ω /2π of the radiation is exactly equal to that of the transition ω 0 /2π. Numerical calculations are made for the situation when the ‘detuning’ δ ═ ω — ω 0 is not equal to zero. Approximate expressions are also derived in terms of δ for use in a later paper which deals with mixed homogeneous and inhomogeneous line-broadening.