Quasistatic theory of optical absorption lines

C. Stehlé, N. Feautrier

The close coupled theory of scattering in a radiation field may be used to describe absorption or emission processes occurring during a collision. Using a semi-classical description of the collision we study the evolution of the collisional complex. The case of atomic hydrogen perturbed by protons is particularly interesting since the exact solution of the dynamical problem is known for a large domain of internuclear distances. In the particular case of the Ly α line we determine the characteristic time of the absorption or the emission. The « impact » and « quasistatic » limits are then analysed.

É. G. Pestov

A universal formula is derived for the spectral line profile of atoms. It describes the whole spectrum, including collisional, intermediate, and quasistatic frequency ranges in the case when optical collisions take place with impurity particles in a strong electromagnetic field which influences the collision dynamics. A new physical effect is predicted: it is manifested by a dependence of the collisional shift of an absorption (stimulated emission) line profile on the intensity of an electromagnetic field.

P Eward, S.V. O’Leary

The technique of excited-state degenerate four-wave mixing, ESDFWM, has been used to monitor the absorption of light at two wavelengths in the extreme wings of the pressure broadened Na D lines. The relative slopes of the ESDFWM signals as a function of pressure of rare gases He, Ne and Ar are compared with predictions of the quasistatic theory of line broadening using theoretical interatomic potentials.