Tunable differential interferometer for optical tomography.

We report the use of a tunable differential interferometer for optical tomography. This interferometer has several advantages over other methods for phase measurements in optical tomography, including good stability, variable sensitivity, and the elimination of fringe ambiguity. Quantitative images of the gas concentrations in subsonic jets of methane and oxygen issuing into air are presented, with absolute accuracies better than 3.5% and 4.5%, respectively.