Two Experiments Involving Atomic Rubidium: 4D Excited State Absolute Photoionization Cross Section Measurements and 5S-5D Two-Photon Degenerate Four-Wave Mixing Studies

University Of Southern Mississippi, Hattiesburg MS

Investigators

Abstract

This award supports two experimental research projects involving atomic rubidium. The first consists of absolute measurements of the photoionization cross-section of the 4D5/2 excited state of laser-cooled rubidium atoms. Photoionization studies are relevant for sensitive and state-selective detection of trapped atomic and molecular species, as well as for plasma research, including ultracold plasma formation. Excited D states are of particular interest for fundamental tests of atomic theory. Rubidium atoms cooled and trapped in a standard magneto-optical trap will be subsequently excited to the 4D5/2 state via a two-step process and subjected to the photoionizing laser. The photoionization rate will be measured versus several ionizing laser intensities and several wavelengths below the photoionization wavelength from which relative photoionization cross sections will be determined. The photoionization measurements will be subsequently put on an absolute scale by performing accurate measurements of the excited state fraction using a charge transfer technique. The experimental results will be compared for consistency with theoretical calculations. The second project involves theoretical and experimental studies of the 5S1/2-5D5/2 two-photon degenerate four-wave mixing in a rubidium vapor cell. Degenerate four-wave mixing is a high resolution spectroscopy technique which can be used to investigate phenomena such as optical pumping, relaxation, diffusion, collision and quenching processes. Potential applications include phase corrections of aberrant optical wave fronts, optical computing, image processing, pattern recognition and others. The two-photon degenerate four-wave mixing signal will be investigated versus the angle between the probe and the forward pump beams for several rubidium vapor cells mixed with helium buffer gas at various pressures. The experimental results will be used in conjunction with a newly developed theoretical model to obtain numerical values for the 5D5/2 excited state diffusion coefficient. Traditionally, participation of Mississippi?s population in science and engineering has been low. Laser cooling and trapping is one of the most active areas in atomic physics research, and such studies are not performed anywhere else in the states of Mississippi, Alabama and Louisiana. The University of Southern Mississippi has a student population that is 25% African-American and 58% female, which makes the university uniquely positioned to make a difference for women students and, specifically, for minority women in science and engineering. The broader impact of the research is reflected in providing undergraduate and graduate students with experimental research opportunities at the forefront of atomic physics, which in turn, will improve science education. In addition, the research will facilitate extensive involvement in high school outreach and recruitment.