Abstract

An enhanced-precision, high-signal method for velocity measurements with photothermal deflection spectroscopy is presented. 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 probe beam, which has a diameter smaller than the fringe spacing. This two-beam pump improves on single-beam pumps because there are more markers for the velocity determination, and the larger thermal gradients increase the probe deflection. The method is illustrated by velocity maps in a laminar ethylene/nitrogen jet using a CO₂ pump laser. Velocity distributions and noise levels were also measured with grid-induced turbulence above the jet.

© 1986 Optical Society of America

Linear imaging of gas velocity using the photothermal deflection effect

Jeffrey A. Sell and Robert J. Cattolica
Appl. Opt. 25(9) 1420-1428 (1986)

Gas velocity measurements using photothermal deflection spectroscopy

Jeffrey A. Sell
Appl. Opt. 24(22) 3725-3735 (1985)

Measurements of very low gas flow velocities by photothermal deflection spectroscopy

Y.-X. Nie, K. Hane, and R. Gupta
Appl. Opt. 25(18) 3247-3252 (1986)

Application of photothermal deflection technique to flow-velocity measurements in a flame

A. Rose and R. Gupta
Opt. Lett. 10(11) 532-534 (1985)

Pulsed photothermal deflection spectroscopy in a flowing medium: a quantitative investigation

A. Rose, Reeta Vyas, and R. Gupta
Appl. Opt. 25(24) 4626-4643 (1986)