Theory of pump-probe spectroscopy using an amplitude approach

A theory of pump probe spectroscopy is carried out using an amplitude appro ach in a bare state basis. The interplay between absorption and emission is clearly defined in this approach. Both closed and open systems are conside red. The theory is applied to a calculation of the dispersion-like structur e that appears when the probe frequency is nearly equal to the pump frequen cy, in the limit of large pump field detuning. The origin of the dispersion -like structure can be traced to interference terms in the absorption spect rum or to a radiative shift. The probe gain which occurs without level inve rsion cannot be viewed as a parametric process, in its normal sense. (C) 20 00 Elsevier Science B.V. All rights reserved.