QUANTUM DYNAMICS AND COOLING OF ATOMS IN ONE-DIMENSIONAL STANDING-WAVE LASER FIELDS - ANOMALOUS EFFECTS IN DOPPLER COOLING

We report computational results for the time evolution of the velocity distribution P(V,t) for two-level and multilevel "Doppler" laser cooling. We compare results obtained from the semiclassical (SC) Fokker-Planck equation and from generalized optical Bloch equations applied to density matrices over a basis of products of internal and quantized translational states (QDM). Computer memory requirements are optimized to make large-scale QDM calculations feasible. QDM and SC agree well except for two cases: (a) atoms in the wells of the light-shift potential (with kinetic energy less than the well depth, U0), and (b) atoms with recoil energy ER comparable to or greater than the natural linewidth Latin small letter h with strokeΓ. Transient dips occur in P(V,t) at V=0 in QDM results due to slow cooling of atoms in the light-shift potential wells. Dips in P(V,t) occur at velocity-tuned-resonance (Doppleron) velocities but disappear over long interaction times as atoms accumulate near points where the force is zero. When ERLatin small letter h with strokeΓ, sharp peaks occur in P(V,T) at V=±VR from velocity-selective population quasitrapping not previously found in a two-level transition. Sharp features in P(V,t) occur also for J→J+1 transitions with J>0, small U0/ER, and sufficiently large detuning, from transitions between individual quantum states in the periodic potential. © 1995 The American Physical Society.