Fellow, American Physical Society

Ph.D., Boston U., 1970.

Research Associate, 1970-74, Assistant Professor, 1974-78, Columbia University.

Assistant Professor to Professor, University of Arkansas, 1978-85.

Chair of the Department, 1989-95.

Visiting Fellow, Princeton University, Fall 1998.

Editorial Board Spectroscopy and SpectralAnalysis (China), 1991-to date.

Books edited: Laser Spectroscopy (AAPT, 1993).

Professor Gupta'sinterest is in atomic physics and laser spectroscopy. He did extensive work in high-resolution (Doppler-free) spectroscopy of alkali-metal atoms before his interests shifted to photoacoustic and photothermal spectroscopy.

COMBUSTION DIAGNSTICS BY PHOTOTHERMAL SPECTROSCOPY

We are engaged in experiments on the application of photothermal deflection spectroscopy to combustion diagnostics. Combustion is a very complicated phenomenon. The burning of even a simple hydrocarbon involves several hundred coupled chemical reactions. For this reason, a thorough understanding of the combustion process does not yet exist. Besides the intrinsic interest in understanding the physics and chemistry of this prevalent natural phenomenon, an understanding of the combustion would presumably lead to the design of highly efficient and/or nonpolluting engines.

The theoretical models of combustion, in general, need to be experimentally verified, and, at times, even to build a theoretical model one needs the experimental data. Hence there is a need for diagnostic techniques, and in general one is interested in measurements of the absolute concentrations of molecular species such as H2O, CO2, OH, CH, NO, etc. and atomic species such as, H, O, and C. Moreover, in addition to the concentrations one is also interested in measurements of local temperatures and flow velocity. We have recently demonstrated that this technique can be used to measure all three parameters of interest, that is, species concentration, temperature, and flow velocity simultaneously with a very high spatial and temporal resolution.

In this technique, a dye-laser beam (pump beam), tuned to one of the absorption lines of the molecules to be detected, passes through the flame. The molecules absorb the optical energy from the laser beam and due to fast quenching rates in a flame, most of this energy quickly appears in the rotational-translational modes of the flame molecules. Thus the dye laser-irradiated region gets slightly heated, leading to changes in the refractive index of the medium. Now if a probe-laser beam overlaps the pump beam, the probe beam is deflected due to the variations in the refractive index of the medium created by the pump beam. Analysis of these deflection signals yields the desired information.

Our current efforts are focused on measurement of atomic hydrogen in flames. Atomic hydrogen is a very important species because it is extremely reactive. A slight change in its concentration can change the flame dynamics completely. However, measurement of atomic hydrogen presents some formidable challenges, least of which is that one needs a laser radiation in the vacuum-uv region of the spectrum (121 nm).