Temperature measurements in a laser-heated gas by quantitative shadowgraphy

A whole-field quantitative shadow method was used to determine the temperature in a laser ignition experiment. An ethylene-air mixture was heated by a CO(2) laser, and the hot gas was illuminated with a collimated laser beam. The resulting shadow image was recorded digitally and analyzed to determine the temperature. Very good spatial and temporal resolutions (15 microm and 10 ns) were achieved using a simple optical arrangement. A computer simulation was used to determine the sensitivity of the shadow temperatures to blurring due to diffraction and uncertainties in parameters such as the ambient pressure. Temperatures determined from Rayleigh light scattering agreed with the shadow measurements to within 1-4%.