Professor and Head, Department of Physics

 also Director of Laser Facility, Member of Institute of Materials Science

 and Photonics Research Center, Affiliate Professor of Chemistry

 B.S., Chemistry, California Institute of Technology, 1964

 Ph.D., Physical Chemistry, Harvard University, 1969

Internet address: stwalley@uconnvm.uconn.edu

Research Specialty: the area of atom, molecule and photon interactions, particularly few atom systems where the interactions can be obtained from diverse fields: spectroscopy, collisions, electronic structure calculations, etc.

 Research In Progress

  Laser Spectroscopy and Photodynamics

 The excitation of atomic or molecular fluorescence using one or more lasers (usually tunable) is now a well known technique which we have applied to a variety of systems with emphasis on the alkali metal vapors. Of particular interest are studies of atomic interactions and potential energy curves, obtained accurately from spectroscopic data, including accurate dissociation energies, long-range interactions and quantitative evaluation of the breakdown of the Born-Oppenheimer approximation (separation of electronic and nuclear motion); and absolute radiative transition probabilities (bound-free as well as bound-bound) for one and more photon transitions in diatomic species such as Na2. Recent emphasis has been on double and triple resonance techniques which circumvent many constraints due to selection rules. In addition, novel studies of state- selected photodissociation and the polarization of atomic fluorescence resulting from photodissociation are underway. Supported by the National Science Foundation (W. C. Stwalley, PI) and the Air Force Phillips Laboratory (through the Hughes STX Corp., W. C. Stwalley, PI)

  Laser Ionization Spectroscopy and Laser-Produced Plasmas

 The production of atomic and molecular ions upon irradiation by one or more lasers has been studied, again with emphasis on alkali metals. Of particular interest are energy transfer and ionization in metal vapors, e.g. the competition between associative ionization, ion pair formation, fluorescence and other processes in collisions of excited alkali metal atoms; and plasmas produced by low power (>= 1 milliwatt) CW laser or modest power pulsed laser irradiation. These unique high electron density (10¹⁴/cm³), low electron temperature (~ 0.1 eV) plasmas have been produced in all alkali vapors by interesting feedback mechanisms. In addition, novel studies of multiphoton excitation of doubly excited autoionizing states is underway. Supported by the National Science Foundation (J. T. Bahns, PI, W. C. Stwalley, Co-PI)

  Laser Development

The use of lasers to optically (and otherwise) pump atomic or molecular transition lasers is a particularly useful spectroscopic tool. We are involved in studies of diatomic optically pumped lasers, and of neutral and ionized excimer lasers (e.g. the violet bands of sodium). Of particular interest is the pumping of such lasers by dissociative recombination (e.g. Na3⁺ + e^- -> Na2^* + Na, where Na2^* is an upper laser level). Supported by the Provost's Economic Development Grant (W. C. Stwalley, PI, J. T. Bahns, Co-PI).

  Studies of Ultracold Atoms and Molecules

 Exciting new laser techniques allow cooling and trapping of atoms at microkelvin temperatures. Such atoms show extreme quantum behavior (deBroglie wavelength is proportional to T^{- 1/2}). Spectra of colliding ultracold atoms provide unique and direct information on the long range interactions between atoms and related atomic properties (atomic lifetime, dipole matrix elements, electron affinity, etc.). We have obtained ~10¹¹ atoms/cm³ at 500 uK in a "dark spot" magneto-optic trap and used this trap to observe the first ultracold photoassociative spectra of K atoms. We plan to extend this spectroscopy from single photon to multiphoton and apply it to the production of ultracold molecules. Current studies are supported by a University of Connecticut Research Foundation grant (W. C. Stwalley, PI, J. T. Bahns, Co-PI) and Prof. Stwalley's startup funds. A major proposal (W. C. Stwalley, PI, P. L. Gould, Co-PI) is pending at NSF (see Making Molecules at MicroKelvin).

  Laser Applications

 Studies of laser heating of diamond, laser welding of polymers and laser production of nanoparticles are underway with support form Norton Co., Worcester, MA; Johnson and Johnson Medical, Inc., Southington, CT; and the Photonics Research Center, respectively.

 Professor Stwalley is also the Principal Investigator on the NSF grant "REU Site in Physics at the University of Connecticut" (R. Mallett, Co-PI).