H. Metcalf

Measurement of force-assisted population accumulation in dark states.

Atoms can be accumulated by velocity-selective coherent population trapping (VSCPT) in dark states of very highly monovelocity, resulting in very narrow distributions. The optical pumping process that permits the population accumulation proceeds by random walk in momentum space and is of limited efficiency. Several authors have predicted that damping forces can enhance VSCPT in carefully chosen laser fields. We present corroboration of this idea with measurements showing increased efficiency for VSCPT.

Nonadiabatic transitions in finite-time adiabatic rapid passage

To apply the adiabatic rapid passage process repetitively [T. Lu, X. Miao, and H. Metcalf, Phys. Rev. A 71, 061405(R) (2005)], the nonadiabatic transition probability of a two-level atom subject to chirped light pulses over a finite period of time needs to be calculated. Using a unitary first-order perturbation method in the rotating adiabatic frame, an approximate formula has been derived for such transition probabilities in the entire parameter space of the pulses.

Observation of Large Optical Forces in Modulated Light

We have observed huge optical forces caused by multiple repetitions of adiabatic rapid passage sweeps with counterpropagating light beams that coherently exchange of momentum between atoms and the light field. It exceeds 10X radiative force.

Laser Cooling in the Quantum Domain: Shedding New Light on Dark States

When atoms are laser cooled to below the single photon recoil limit, their deBroglie wavelengths become comparable to or larger than the wavelength of light used to cool them. To describe properly the physics in this regime, it is necessary to quantize the external (atomic momentum) degrees of freedom. We describe here several 1-d laser cooling experiments in this quantum regime with metastable helium atoms that demonstrate several novel features in subrecoil laser cooling.

Laser Cooling with Intense Laser Fields

We have performed laser cooling of a Rb atomic beam at high laser intensities using two different laser configurations: a transverse lin 1 lin configuration and magnetically induced laser cooling (6’-MII,C1). The resulting velocity distribution is determined from the spatial distribution of the atoms as measured by fluorescence detection using a CCD camera.