EFFECTS OF TEMPERATURE ON THE ABSORPTION LINE-SHAPE FUNCTION FOR DRIVEN 2-LEVEL ATOMS - A NON-MARKOVIAN TREATMENT

The description of a non-Markovian process is presented and the asympt otic solution of the generalized master equation is obtained for a two -level atom pumped externally by a monochromatic time-dependent electr ic field. We give the explicit expression for the absorption line-shap e function and discuss its features as a function of the temperature a nd the memory parameter. We verified the following interesting results : (a) At a critical temperature the line shape undergoes a phase trans ition, the single-bump profile splits into two bumps; (b) for small va lues of the memory parameter k the linewidths broaden, becoming larger than the ones calculated under the Markovian approximation, and after reaching some maximum value they narrow monotonically with increasing values of k, this behavior being standard for any finite temperature.