RUI: Atomic Physics with Rapidly Frequency Chirped Laser Light

Adelphi University, Garden City NY

Investigators

Abstract

This project will study the how collisions between ultracold atoms can be controlled by an external laser field. These experiments will lead to a greater understanding of light-assisted collisions and simple chemical reactions. The major advancement in this project is that the laser will be pulsed on a time scale, and chirped over a frequency range, commensurate with the atomic collision process. Using ultrafast lasers, related experiments on much faster time scales have led to a greater understanding of light-assisted chemical reactions. However, because atoms in the planned experiments will be very cold, the new experiments can be conducted on significantly slower time scales. This team has already developed a novel amplitude and phase modulated laser system for these experiments. This laser system will also be used to explore new methods for controlling atomic excitations. This is important for slowing atoms and is an interesting avenue toward slowing molecules to a stop. These activities provide an ideal environment for undergraduate physics students to conduct exciting physics and experiments, use lasers to control quantum mechanical excited-state collisions, and explore new techniques for preparing ultracold molecules. Engaging students in undergraduate research is a high-impact teaching practice and helps to generate trained scientists. Both of the projects are centered on a novel laser system to generate intense frequency-chirped pulses of laser light. This laser will be used to affect a variety of dynamics in atomic physics, including coherently controlling ultracold collisions and studying rapid adiabatic passage. In the first project, this team will use loss from a magneto-optical trap as a tool to explore coherently controlling trajectories in inelastic light-assisted collisions between atoms. Recent work has shown that ultracold collisions between two rubidium atoms can be controlled with frequency-chirped laser light; typically the entire process takes about one nanosecond. By tuning the laser frequency and amplitude on that same time scale, one can influence the behavior of the collision and the entire process can be coherent. The initial experiments have shown that this is the case using a 1 GHz in 100 ns laser pulse; however, the experiments weren't fast enough to observe total control over collisional processes. This team has shown, using semi-classical simulations, that a modest increase in the chirp-rate leads to full control over collisional processes of this type (1 GHz in 20 ns). This project now aims to show that shaping laser pulses on the one nanosecond time scale can lead to control over collisions in a novel way. In the second project, this team will explore shaped frequency-chirped laser light as a means to accelerate atomic gases. They will do this by using a pair of counter propagating frequency-chirped pulses delayed by much less than the lifetime of the transition. This will work with a Doppler broadened gas because the range of chirp is large and rubidium is heavy. Successful developments on this project may increase the likelihood that coherent processes will be used to slow molecular beams (SrF, CaF, etc), for cold and ultracold molecule experiments. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.