Tomographic imaging of fluid flows by the use of two-tone frequency-modulation spectroscopy

Abstract

Diode laser absorption measurements obtained with two-tone frequency-modulation spectroscopy (TTFMS) are combined with tomography to produce spatially resolved quantitative images of fluid flows. The high sensitivity, good accuracy, and high stability of TTFMS absorption measurements permit optical-absorption tomography to be performed with low noise on extremely weakly absorbing objects. The method is demonstrated on a small oxygen flow with a GaAlAs diode laser operating near 760 nm and with an absorption sensitivity of 1:10(6).