Photothermal deflection method of measuring fluid velocity

Details Photothermal deflection method of measuring fluid velocity Photothermal deflection method of measuring fluid velocity

1984-09-10

1987-03-31

Krass, Errol A.

Boots, shoes, and leggings

356 28, 356128, 356129, 73204, 7386105, 734321, 364565, G01F 168, G01N 2141

Patent

active

046548033

ABSTRACT:
A method of measuring the velocity of a fluid by noninstrusive means comprises passing a pump laser beam pulse through the fluid wherein the fluid contains a constituent absorbing the wavelength of the laser so that a temperature gradient, and therefore an index of refraction gradient, occurs in the laser beam path; and a probe laser beam is passed transverse to the pump laser beam and is deflected by the heated portion of the fluid; measuring the beam deflection and calculating from that the fluid velocity. After the pump pulse the amount of deflection reaches a peak value and then decreases at a rate independent of the concentration of the absorbing constituent. Where the pump laser beam has a Gaussian spatial profile, the deflection signal decreases according to: exp-2(v+/a).sup.2, where v is the velocity; t is time; and a is a constant representing the pump laser beam radius. The apparatus is similar to that used for photothermal deflection spectroscopy and involves a pair of crossed laser beams--one for pumping the medium and one for probing the medium; a probe beam deflection sensor; and electronic circuitry for analyzing the measured deflection signal.

REFERENCES:
patent: 3807228 (1974-04-01), Matzuk
patent: 3950104 (1976-04-01), Munk
patent: 4480483 (1984-11-01), McShane
W. Herrmann & D. Pohl, "Trace Analysis in Gases by Laser-Induced Schlieren Technique", IBM Technical Disclosure Bulletin, vol. 21, No. 10, 3/79, pp. 4208-4209.
K. Shib et al., "Sehlieren Technique for the Measurement of Low-Level Concentration Fluctuations," Rev. Sci. Instrum., vol. 50, No. 9, 9/79, pp. 1080-1083.

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