Walter Lempert is a Professor with joint appointment in the Departments of Mechanical Engineering and Chemistry. He received his Ph.D. in Physical Chemistry from the University of Utah in 1981. Prior to his arrival at OSU in 1997 he spent two years as an NRC Post-doctoral Fellow at the National Bureau of Standards, five years at NASA, and 9 years at Princeton University. Current research interests center on the development and application of optical techniques for probing energy transfer and nonequilibrium plasma phenomena. He is currently a member and past chair of the American Institute of Aeronautic and Astronautics Aerodynamic Measurement Technology Technical Committee. 

My research focuses on the application of atomic and molecular spectroscopy to problems of engineering interest. The work is inherently interdisciplinary, combining such diverse subjects as nonlinear optics, fluid mechanics, plasma physics, and energy transfer. In a broad sense, current research topics can be divided into three areas; studies of the influence of chemical and internal mode nonequilibrium on gas phase chemical reaction rates, fundamental studies of non-equilibrium plasmas, and development and application of advanced laser-based diagnostic tools, including ultra high frame rate (~MHz) planar imaging. A major thrust of my current work involves the use of high voltage (~20 kV) – short pulse duration (~10-100 nsec), high repetition rate (~10-100 kHz) pulsed discharge plasmas. These plasmas exhibit inherently high stability and spatial uniformity at high pressure (See photo below), relative to other more common types of plasmas, resulting in potential application to a wide variety of practical applications. We are performing a variety of research programs which are centered on the physics and chemistry of such plasmas, the primary goals of which include: (i) Optical diagnostic studies of the fundamental properties of such plasmas, in particular the space and time-resolved evolution of the electric field and electron kinetic energy distributions, (ii) Use of these plasmas for efficient excited species and radical production to facilitate ignition and flameholding in combustible mixture flows, and (iii) Elucidation of the kinetic mechanism for low temperature generation of air species such as NOx , as well as chemical oxidation and ignition of common gas phase fuels. These studies utilize a wide variety of laser-based diagnostic tools including single and two photon laser induced fluorescence, for quantitative measurement of species number densities, nanosecond and picoseconds Coherent Anti-Stokes Raman Spectroscopy (CARS) for measurement of rotational temperature, vibrational distribution function, and electric field, and Thomson scattering, for measurement of electron density and electron energy distribution.

Photograph of diffuse, volumetric, highly non-equilibrium air plasma created by 40 kHz repetitively pulsed nanosecond discharge. Rotational / Translational temperature is ~400 K whereas electron temperature exceeds 50,000 K.