Measurement of the effective optical path length of diffusing integrating cavities using time-resolved spectroscopy

A method to measure the effective optical path length (EOPL) of a diffusing cavity using time-resolved spectroscopy is presented. A 710 nm short-pulsed laser was employed as the light source with a FWHM of 0.7 ns. From the temporal response curves, the time to establish a uniform optical field was obtained as approximately 4 ns for this cavity. Correspondingly, light was scattered 5-6 times by the inner coating. EOPLs with different port fractions were obtained by the selection of an appropriate initial time. Moreover, we verified a previously reported theoretical EOPL law using time-resolved spectroscopic results. This work provides a method to measure the EOPL of a diffusing cavity at different wavelengths.