William G. Tong
Distinguished Professor of Chemistry
Analytical Chemistry
Research Interests
Research in our laser laboratory is directed toward the application of novel
nonlinear multiphoton laser spectroscopic methods in the development and understanding
of new methods in laser analytical spectroscopy. Emphasis is placed on the understanding
of fundamental principles and experimental observations of new spectroscopic
phenomena. Integration of innovative nonlinear laser techniques and computer
interfacing of high-precision instrumentation provides many advantages with
new experimental possibilities over conventional laser spectroscopic methods
in analytical problem solving.
Novel laser methods, such as nonlinear wave-mixing spectroscopy, offer parts-per-quadrillion-level
detection sensitivity at excellent Doppler-free spectral resolution for elemental
analysis, and sub-attomole (e-18 mole) detection sensitivity for molecular analytes.
By using low-pressure cells such as discharge plasmas, Lorentzian (pressure)
broadening is also minimized and, hence, spectral resolution is further enhanced.
Optical phase conjugation by degenerate four-wave mixing offers excellent detection
sensitivity because optical signal detection is very efficient since the signal
is a coherent time-reversed replica of the original probe laser beam. Application
of these novel laser methods in chemical analysis has provided significant improvements
in sensitivity, selectivity, reliability, and spectral and spatial resolution
to levels previously thought impractical in many different atomizers or sample
holders including discharge plasmas, graphite furnace atomizers, inductively
coupled plasma atomizers, and analytical flames. Wave mixing can be also conveniently
interfaced to liquid chromatography, capillary electrophoresis, microchips,
lab-on-a-chip, microarrays and other microfluidic systems for biomedical applications.
Continuous-wave lasers, such as ring lasers, argon-ion lasers, solid-state
diode lasers, tunable external cavity diode lasers, and pulsed lasers, such
as excimer and Nd:YAG pumped dye lasers can be used. These nonlinear spectroscopic
methods provide spectral resolution high enough for the study of atomic hyperfine
structures and analysis of isotopes in many research areas including biomedical
and environmental sciences. We are also interested in fast laser-powered pyrolysis
with laser-induced diagnostic monitoring of reaction rates and mechanisms of
semiconductor materials. Real-time monitoring of intermediate species could
provide better understanding of fundamental physical and chemical processes.
These patented novel nonlinear laser methods yield ultra trace detection sensitivity
while maintaining isotope-level chemical selectivity, and hence, they offer
new ways of diagnosing mineral poison/deficiency without using radioactive isotopes
as biotracers. Trace amounts of isotopes can be fingerprinted at higher resolution.
Potential applications include earlier detection of diseases, better design
of cleaner drugs, and more sensitive detection of pollutants and chemicals both
inside the human body and in the environment.
Selected Publications
- Weed KM, Tong WG "Trace analysis of rubidium hyperfine structure in
a flame atomizer using sub-Doppler laser wave-mixing Spectroscopy," APPLIED
SPECTROSCOPY 57 1455-1460 (2003). This paper was featured on the cover of
Applied Spectroscopy (see below).
- United States Patents (2000 and 1997), United States Patent in progress
(2004).
- Mickadeit FK, Berniolles S, Kemp HR, Tong, WG "Sub-parts-per-quadrillion-level
graphite furnace atomic absorption spectrophotometry based on laser wave mixing,"
ANALYTICAL CHEMISTRY 76 1788-1792 (2004).
- Maniaci M, Tong WG "Multiphoton Laser Wave-Mixing Absorption Spectroscopy
For Samarium Using a Graphite Furnace Atomizer", SPECTROCHIMICA ACTA,
Part B, 59, 967-973 (2004).
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