Photothermal Spectroscopy
Application of novel optical methods of chemical analysis is the main research topic
of this laboratory. New ways to perform photothermal spectroscopy in homogeneous and
heterogeneous media are being studied. Nonlinear optical
absorption effects found to occur in the analysis of gaseous and condensed phase
samples are used to increase analytical information, and facilitate excited state energy
transfer, relaxation kinetics, and excited state absorption cross section determinations.
These intrinsically nonlinear systems are not reversible on the measurement time scales,
adding to analysis complexity. Analysis is possible using an integrated computer
acquisition and data analysis approach. Several tools, including smart, optical and
digital filter based data collection, symbolic language processors, spreadsheets, and
regression software, are integrated to allow rapid data analysis and model testing.
For a short list of photothermal and photoacoustic related WWWeb sites of mostly tutorial
material click here.
White-Light Spectrometry
In related experiments, conventional white light sources are
used to excite photothermal signal response in homogeneous samples. The photothermal
signal is a secondary effect, generated by the absorption of power or energy from the
excitation light source. It is found that the white light source can result in signal
generation, independent of the absorption spectrum. This allows non-specific detection.
The premiere report on this work is published in a special issue of Optical Engineering
devoted to photothermal spectroscopy. A version of this
apparatus for laser excitation sources is also described.
The MS Power-Point
presentation given at the 1999 La Jolla photothermal conference is here.
White-Light Applications - White-light photothermal spectrometry and related
techniques are being applied for liquid chromatography detection and to determine heats of
reaction of photochemically initiated processes without interference from specific volume
change effects.
Fluorocarbon Analysis
Another research emphasis concerns the detection of trace fluorocarbon substances in
the atmosphere. These compounds, known as alternative fluorocarbons
(AFC), are being used to replace chlorofluorocarbons
(CFC) now known to deplete stratospheric ozone. At present, we are evaluating
conventional, ECD, FID, etc., and non-conventional, Atomic Emission, methods for detecting
these species. Quantitative in situ measurements will allow model testing of the
effect that these new substances have on stratospheric ozone depletion and global warming.
Soil Physics Research
We are investigating the structure of water adsorbed onto soil
particles. This NSF funded research is being performed in collaboration with soil chemists
and physicists in the Department of Plants, Soils, and
Biometeorology. The research will result in a better understanding of the microscopic
nature of water adsorbed to soil particles. A better understanding of the soil-water
interaction is necessary to predict transport of nutriants and pollutants through soils. AC impedance analysis of some
Montmorillonite soil samples can be found here.
Digital Filtering
Real time digital and optical signal processing methods are
being developed to maximize the precision of data collected in the laboratory. Several
methods for data smoothing, regression, and deconvolution of Poisson (shot-noise) data
have been developed. Free software (in code form) is often available by sending me an e-mail request. Our chemometrics research
departs from the use of commercial programs. Currently completed projects for which C
language programs may be obtained include the Gaussian smoothing filter,
Expectation-Maximization (EM) for smoothing, regression, and deconvolution, and EM based cosine transforms for FTIR interferogram data.
Go here for links to digital signal processing sites. Try this to obtain subroutines and code.
Present and former students and postdoctorals
Page last checked or edited Tuesday, August 03, 2004