Bryn Mawr College

Atomic, Molecular, and Optical Physics
Laser-based studies of atomic and molecular excited-state structure and decay dynamics, including Rydberg state dynamics, photoionization, autoionization, predissociation, and photodissociation. Nonlinear optical techniques including multiphoton excitation and resonant four-wave mixing spectroscopy. 

Laser Trapped Mirrors in Space
Supported by the Mellon Foundation and NASA's Institute for Advanced Concepts, a collaboration of physicists and astronomers have investigated the feasibility of using laser light to construct ultra-light weight large mirrors for space-based astronomical research.  Click here to go to the project web site.

Current Projects
In our photophysics laboratory we perform laser-based studies of atomic and molecular excited-state structure and decay dynamics by using a variety of spectroscopic techniques. Areas of interest include photoionization, autoionization, predissociation, photodissociation, doubly-excited electronic states, long-range molecular states, ion spectroscopy, transient excited states as intermediates in collision complexes, electronic and nuclear coupling, molecular Rydberg states, and multichannel quantum defect theory. Current work involves using nonlinear optical techniques such as multiphoton excitation and detection, laser-induced grating spectroscopy, and degenerate four wave mixing to probe the excited-state structure and dynamics of fundamental small molecules. Experiments are carried out in a photophysics laboratory equipped with a pulsed supersonic molecular beam source which can produce stable and transient species, a differentially-pumped vacuum system, and two Nd:YAG-pumped pulsed dye laser systems with associated doubling crystals, optics, and data acquisition equipment.

One of our projects has involved using time-resolved four-wave mixing spectroscopy to make high-resolution measurements of molecular hyperfine structure. The data shown above is an example that reveals quantum beats due to coherent excitation of the hyperfine structure of the first electronically excited state of nitric oxide. This nonlinear optical technique has a state-selectivity not available with linear quantum beat techniques and also allows direct measurements of ground state structure. We have developed a model using diagrammatic perturbation theory and a spherical basis analysis to describe the laser polarization dependencies of the signal. These dependencies allow a certain amount of control over the optical-matter interactions which interfere to give the beats.

Our latest project involves using a multiphoton ionization technique to excite a series of unusually long-range states of molecular hydrogen located in energy above the ionization limit and second dissociation limit.  Due to their large average internuclear separation, theses states are remarkably stable.  By recording their term energies and line-widths we are probing their structure and dynamics.  While the energies of the rovibrational levels of many of these states have been predicted by ab initio theory, most have not yet been observed experimentally because they are very difficult to populate.  We have been able to exite many levels of these previously unobserved states by using our ability to generate radiation at 193 nm to populate the E,F, v=6 state as an intermediate step in our excitation scheme.

Publications describing our work can be found here.  A list of previous and current graduate and undergraduate research projects can be found here.  This work has been supported by the National Science Foundation through the CAREER and regular award programs.