ANDREAS MANDELIS is Director of the Photothermal and Optoelectronic Diagnostics Laboratory at the University of Toronto and Professor of Mechanicaland Electrical Engineering. His current research interests include areas of solid-state thermal-wave gas sensors, novel photothermal instrumentation and techniques, the physics of thermal waves and tomographic developments, deep level electronic defects and the study of nonradiative quantum efficiencies in solid-state laser materials. He is the author of more than 100 published papers and the editor of a number of well-received books on photothermal and photoacoustic science and technology.He is on the Executive Committee of the Instrumentation and Measurement Science Topical Group of the American Physical Society and a member of the Center for Hydrogen and Electrochemical Studies of the University of Toronto. Dr. Mandelis holds a BS in physics from Yale University and advanced degrees in applied physics and material science from Princeton University. CONSTANTINOS CHRISTOFIDES is Assistant Professor in the Department of Natural Sciences at the University of Cyprus, in Nicosia. His major interests include the development of new devices, applied optics, advanced materials, and solar energy. He is a member of the American Physical Society, the Canadian Association of Physicists, the Spectroscopic Society of Canada, and the International Solar Energy Society. Dr. Christofides holds advanced degrees in physics, applied physics and energy physics from Grenoble University, in France. In addition, he was a postdoctoral fellow at Sherbrooke University, and a research associate and lecturer with the Photothermal and Optoelectronic Diagnostics Laboratory at the University of Toronto.