Stimulated Raman adiabatic passage with partially coherent laser fields

In this paper we discuss the effect of phase noise upon the efficiency of population transfer produced by stimulated Raman adiabatic passage (STIRAP). To allow an adjustable cross-correlation of the two fields we consider the pump and Stokes pulses to be derived from a single phase-diffusing exponentially correlated laser, but we allow some time delay T between the noise signals. We present examples of Monte Carlo simulations, showing unexpected regularities in the dependence of efficiency upon pulse area for partially cross-correlated fields: efficiency does not monotonically increase with increasing pulse area, as would be expected. We explain these, and other properties, by using a simple model of pulse shapes to derive analytic expressions for efficiency. Although derived for a specific analytic form, the formulas also provide a useful description of transfer efficiency by other pulse shapes. We also obtain an estimate of the fundamental limit on the transfer efficiency with STIRAP, based on the Schawlow-Townes limit to laser bandwidths