Fluid flow measurement capabilities of a traveling wave laser oscillator (or ring laser) are assessed theoretically and experimentally. The feasibility of this alternative optical technique for measuring gas flow profiles without insertion of a mechanical probe is examined. Measurements are reported for a range of Reynolds numbers including both laminar and turbulent flows and for a variety of tube diameters. The experimental results are compared with the theory of conditions preceding the establishment of the equilibrium laminar flow profile in round tubes.
Paul Fenster and Walter K. Kahn, "An Optical Technique for Measurement of Gas Flow Profiles Utilizing a Ring Laser," Appl. Opt. 7, 2383-2391 (1968)