Abstract

The collisional steady state and adiabatic-following approximations find extensive use in many areas of nonlinear optics. The deficiencies of these approximations are well known: The collisional steady state approximation is valid only for monochromatic (cw) radiation, and the adiabatic- following approximation is valid only when the damping is zero and the product of the detuning and a characteristic time is much larger than one. We present two improved perturbative approximations for the inversion and polarization of collision- ally broadened two-level atoms induced by a time- dependent field. The new approximations for the polarization are valid to any desired order in the derivatives of the field and inversion. Comparison with the numerical solution of the full density-matrix equations of motion demonstrates that the new approximations significantly improve on the adiabatic-following and collisional steady state approximations for time-dependent pulses in the appropriate damping regime.

© 1989 Optical Society of America