This RUI research project will measure collisions between excited-state atoms with the purpose of studying molecular structure and exploring collision theory. The primary goal is to bridge the velocity gap between traditional collision studies (done at thermal, i.e., warm temperatures in gas cells) and experiments carried out in ultracold traps. The experimental procedure makes use of narrow-bandwidth diode lasers to select thin velocity components of a thermal cesium beam. Collisions between precisely controlled velocity components lead to associative ionization, where two excited atoms form a molecular bond by ejecting an electron to carry off excess energy. The narrow-bandwidth diode lasers also allow control of atomic orientation and alignment, which are important parameters in collision theory.
For the case of cesium, associative ionization offers a simple, but important example of chemical bond formation, involving one-electron bonds. This simplicity makes associative ionization of cesium a good test of collision theory. Beyond evaluating theories and understanding collision processes in sub-Kelvin environments, the broader impact of this project includes enhancing the research and teaching infrastructure of Lafayette College and training future physicists destined for graduate school and employment in industry. Undergraduates are provided with practical hands-on laboratory experience by participating directly in this research. The integration of various aspects of this project into the undergraduate laboratory curriculum provides a second avenue through which students are exposed to modern laboratory techniques.
Using our atomic beam apparatus and precision laser-spectroscopy setup, we have undertaken a significant initiative to measure atomic structure parameters of the excited states of atomic cesium. These measurements are important for a number of applications. These include predicting transition rates in atoms, estimating cold and long-range molecular interactions, optimizing optical cooling and trapping schemes, determining electric-field strengths in plasmas, and, most importantly for us, benchmarking atomic-structure calculations. NSF funding has been central in completing construction of our experimental apparatus. We have used this apparatus to measure atomic hyperfine structure and atomic polarizabilities. Hyperfine measurements quantify the degree to which an atoms electronic structure interacts with its nuclear structure. The polarizability measures the influence of external electric fields on atomic structure. We measured the hyperfine coupling constants for the 7d(j=3/2) state of cesium. These measurements provided a significant increase in precision over values reported in the literature, and we published these measurements in a peer reviewed journal (Physical Review A). We have measure the hyperfine coupling constants and polarizabilities of the excited 6d(j=3/2) state cesium. This lead to a fruitful collaboration with theorists the University of Delaware and the University of Nevada, Reno. Together, we have published these measurements along with the associated theory in Physical Review A. These results were the first 6p polarizabilities measurements reported in the literature. Most recently, we measured the polarizabilities of the 8s and 9s states of cesium. Our 8s results are in very good agreement with theory and previous measurements. Our 9s results also agree with theory, but there have been no previously measurements published. We have submitted these results to Physics Review A. During the course of the award period, we have also conducted preliminary studies on the 5d states of cesium. These states are poorly studied, but are of interest to theorists. One reason that these states have not been the subject of significant research is that they are difficult to access using tradition spectroscopic techniques. We therefore began developing new tools for studying the structure and dynamics of these states. These techniques revolved driving the 6s-->6p single-photon magnetic quadrupole transition. We detect this transition in an atomic beam using photoion spectroscopy, and in a vapor cell using laser-induced fluorescence. In the cell, we have developed a modified saturation technique for achieve sub-Doppler resolution. Educational activities have also been an important aspect of this project. These activities include the training of five undergraduate research assistants. These students have learned important laboratory skills relevant to high-precision spectroscopy, vacuum technology, data analysis, and the reporting of scientific findings. Three of these students have written senior honors theses based on this project and are now pursuing Ph.D. degrees at top ranked Universities. The other two are still enrolled at our College, and they plan on continuing their work on this project into the future. Both have had their interest in pursuing graduate education re-enforced. The PI has also integrated some of our experimental techniques into the College's Advanced Physics Laboratory course. Students in this course are introduced to some of the same high-precision laser spectroscopy, mass spectroscopy, and vacuum techniques used in the above described research. All three topics are important experimental techniques that are not commonly introduced at the undergraduate level. Familiarity with these topics should help prepare our students for continued study in graduate school as well as for work in industry. Overall, this award has had a dramatic positive impact on the research and teaching infrastructure at Lafayette, and it has helped produce substantial scientific results as well as training for future scientists.
