Determination of the effective optical path length of integrating cavity by measuring emitted light

The port fraction in an integrating cavity is defined as the ratio of the area of all the leaky ports to the total internal surface area of the cavity. It allows for the regulation of the cavity’s output radiation flux, thereby influencing the formed light field within the cavity. Building upon this fundamental parameter, we present a technique for determining the effective optical path length (EOPL) of an integrating cavity by examining the output light's variation as a function of port fraction. A relationship between the EOPL and cavity parameters has been established without the presence of gas absorption. To corroborate the method, we calculated the EOPL of the cavity at 764 nm employing both our proposed method and the gas absorption-based approach. Upon comparison, it was observed that the two methods yielded consistent EOPL results, specifically 109.5 (2) cm and 109 (2) cm, respectively. This study demonstrates that the output light from an integrating cavity indeed conveys information about its EOPL in the absence of gas absorption. This insight holds significant value for determining the EOPL of integrating cavities as well as other optical cavity types.