Abstract

A new technique for measuring a single spatial component of gas velocity at many points simultaneously along a line using the laser-induced photothermal deflection effect is presented. In this technique a pump beam from a CO₂ laser is focused and crossed with a planar probe beam from an argon laser above a low velocity gas jet. When the CO₂ laser is pulsed, an ethylene/nitrogen mixture flowing out of the jet absorbs it; the resulting temperature and index of refraction gradient deflects the probe beam plane. The velocity distribution across the jet strongly affects the shape and amplitude of the probe beam deflection. The deflection is recorded with a high-speed 2-D array camera and the images are processed to give the velocity distribution across the jet. Velocities were measured for four different flow rates and also for a shear layer. The velocity distributions have the expected parabolic shape and the peak velocities agree with those calculated from the flow rate. A previously derived expression for the deflection angle was used to calculate the deflection of the planar probe beam as a function of time. The calculated images appear very similar to the measured ones.

© 1986 Optical Society of America

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)

Velocimetry in laminar and turbulent flows using the photothermal deflection effect with a transient grating

Cameron J Dasch and Jeffrey A. Sell
Opt. Lett. 11(10) 603-605 (1986)

Quantitative photothermal deflection spectroscopy in a flowing stream of gas

Jeffrey A. Sell
Appl. Opt. 23(10) 1586-1597 (1984)

Time-resolved crossed-beam thermal lens measurement as a nonintrusive probe of flow velocity

Wayne A. Weimer and Norman J. Dovichi
Appl. Opt. 24(18) 2981-2986 (1985)