Stephen C. Foster

Associate Professor of Physical Chemistry

 
Stephen C. Foster Stephen Foster graduated from the University of Manchester in England in 1978 with a B.Sc. in Chemistry, and in 1982 received a Ph.D. in physical chemistry from Dalhousie University in Halifax, Canada.

After an appointment at the Canadian National Research Council's Herzberg Institute for Astrophysics he worked as a postdoctoral fellow at the Ohio State University. He joined Mississippi State University in 1994 as an associate professor of chemistry.
email:
telephone: (662) 325-8854
 

Research Interests

My group's recent interests include the interpretation and identification of new highly reactive ions and free radicals, the trace-level detection of pollutants and other hazardous agents, and lower-power upconversion of visble and near infrared light..

Hollow Cathode Absorption Spectroscopy

The spectrum below is a small portion of the triply-degenerate deformation mode of the NH4+ ion. Each line corresponds to a change from a single rotational level in the ground state to a different rotational level in the excited vibrational state.

Cavity Ring-Down Spectroscopy

A cavity ring-down experiment can be visualized as a 3 step experiment:

  1. Laser light is injected (and trapped) into an optical cavity (e.g. a pair of highly-reflective mirrors).
  2. The light bounces back and forth between the mirrors and will make many round trips before it all "leaks" out through the mirrors.
  3. The light leaking out through an end mirror is monitored, and the time taken for the signal to fall from I0 to I0/e is recorded (the ring-down time).

In an empty cavity, the ring-down is long; only a tiny fraction of the light is lost each time the pulse hits a mirror. However, if an absorber is placed in the cavity, the light is removed (absorbed) more rapidly by that species and the ring-down shortens. If the ring-down time is plotted as a function of wavelength we generate a very sensitive absorption spectrum.

In this lab, we have applied the method to liquid samples. We are continuing to explore the method and to apply it to important new systems.

Low-Power Optical Upcoversion

Upconversion is the process of taking low energy (long wavelength) photons and converting them to higher energy (shorter wavelength).  The most familiar example is the second-harmonic generation used to convert two high-power Nd:YAG infrared photons  (at 1064 nm) into one green photon (at 532 nm).  We are exploring a process which allows the use of Ru-based sensitizers and substituted anthracene compounds to upconvert low-power red and near-infrared photons into green and blue wavelengths.  To date we have demonstrated the upconversion of a low-power helium-neon laser from 633 nm to blue light at 413 nm.  Work will continue in an attempt to move the long-wavelength input limit into the near infrared.

Publications 2003 - 2008

Other Selected Publications

  1. "Diode laser spectroscopy of the ν1 and ν3 bands of SD3+", with C. Xia and M. M. Sanz, J. Mol. Spectrosc., 188, 175-181 (1998).
  2. "Structures and vibrational spectra for protonated carbonyl sulfide", with S. Saebø and M.M. Sanz, Theoretical Chemistry Accounts, 97, 271-276 (1997).
  3. "The ν4 band of ammonium", with J. Park, C. Xia, and S. Selby, J. Mol. Spectrosc. 179, 150-158 (1996).
  4. "Infrared spectroscopy of the products of a corona excited supersonic expansion", with K. R. Comer, Chem. Phys. Lett. 202, 216-220 (1993).

For a complete list of my publications please look at my resume.