Velocity Selective Resonances from a Novel Optical Force

The strength of optical forces on atoms derives from the rate of exchange of momentum between light and atoms.  We describe the use of multiple Adiabatic Rapid Passage (ARP) sequences to increase both the excitation and emission rates, and thereby strengthen the optical force to F_ARP » F_rad  Ξ ħkγ/2.  This huge optical force results from coherent momentum exchange between atoms and light at a high repetition rate.  It is done with counterpropagating beams of chirped, pulsed light that alternately produce absorption followed by stimulated emission [1], and has been demonstrated for atoms initially at rest.  We have explored how this very strong force depends on atomic velocity and found surprising enhancement at certain velocities [1].    These will be discussed but they seem to occur when atoms travel approximately an integer number of wavelengths between ARP pulses.  The current detector resolution is limited by the longitudinal velocity spread of atoms in the beam, but we are building a new velocimetry system that will ameliorate this.

1) We acknowledge laboratory help from Mike Dapolito and Eric Jones