Abstract

The first velocity measurements in a turbulent flow using photothermal deflection spectroscopy have been made using a new enhanced-precision high-signal method. A transient refractive-index grating is formed by the interference of two pulsed pump-laser beams in an absorbing gas. The motion of the grating is detected by the oscillatory deflection of a crossed probe beam which has a diameter smaller than the fringe spacing. This two-beam pump improves on previous PDV methods using single-beam pumps because there are more markers for the velocity determination, and the increased thermal gradients increase the probe deflection. The method is illustrated by velocity maps in a dilute ethylenejet.

© 1986 Optical Society of America