Research Accomplishments
Dan Elliott’s research efforts over the years have been focused on fundamental laser interactions with atoms and small molecules. His were some of the earliest demonstrations of two-pathway coherent control. He has made contributions to the fields of ultra-cold molecules, phase conjugate four-wave mixing, photoelectron angular distributions, and laser bandwidth effects. He has had the pleasure of working with many talented colleagues during the course of these studies. In the following, we give a brief summary of some of these research areas.
Coherent Control: This is perhaps the research carried out by Elliott which has attracted the most attention. In two-pathway coherent control, we drive an optical interaction in an atom or small molecule by two distinct pathways, such as a one-photon (linear) interaction and a two-photon interaction with light whose frequency is precisely half that of the linear process. When the two optical fields are mutually-coherent, the amplitudes for these distinct interactions can interfere, and we are afforded a degree of control over the outcome of the interaction. Using this technique, we have been able to control the ionization rate of atomic mercury, and control the angular distribution of photoelectrons ejected from atomic rubidium and molecular NO. More recently, we have applied this technique to measurements of extremely weak transition moments in atoms, such as first-order forbidden magnetic dipole transition in atomic cesium. We are now working towards a new measurement of the weak-force induced parity nonconserving (PNC) transition amplitude for the 6s-7s transition in atomic cesium and a parallel measurement of the and PNC amplitude of the ground state hyperfine transition in atomic cesium.
Ultra-cold Molecules: In a collaborative program with Yong Chen, we have been exploring the production and properties of the dipolar, heteronuclear molecule LiRb. We create these molecules in a dual-species magneto-optical trap (MOT), where we cool and trap overlapping clouds of atomic 7Li and 85Rb. The associate these molecules by tuning an infra-red laser to any of a number of bound excited molecular states. The most fruitful photoassociation (PA) resonance that we have discovered to this point in a 4(1)-2(1) long-range state, with which we generate molecules at a rate of ~106 molecules/second. These excited molecules decay to a wide distribution of vibrational levels of the ground X 1S+ state. We estimate a generation rate of ~300 molecules/sec in the lowest vibrational (v=0) level, and ~35% of these molecules find themselves in the v=43 level.
Phase conjugate four-wave mixing: Using a stabilized cw dye laser and optical pumping techniques, we were able to test the fundamental theory by Abrams and Lind of phase conjugate four-wave mixing in an idealized two-level system.
Photoelectron angular distributions: Using pulsed dye lasers and atomic beam techniques, we have explored several fundamental studies of low order atomic photoionization. We measured the rapid energy dependence of the photoelectron angular distribution (PAD) near the Cooper minimum of atomic Rb and Cs, and we showed the complete characterization of the continuum wavefunction using elliptically-polarized light.
Laser Bandwidth effects: Using synthetically generated laser fields, Dan Elliott and co-workers have explored models of the effect of laser bandwidth on a variety of nonlinear optical interactions, including two-photon absorption, saturated single-photon interactions, and four-wave mixing. The synthesized broad-band fields include the phase diffusion model, the real Gaussian field (amplitude fluctuations) and the random telegraph field.