As the volumetric gas flow rate increases to a 3:1 gas-to-liquid feed ratio, the loss in photon absorption becomes more pronounced. These results indicate that larger gas bubbles are associated with a further reduction in the effective optical path length, as the flow regime remains in slug flow. Nonetheless, when comparing the expected path length based on the feed ratio to the fitted path length, it is evident that the decrease in photon absorption is significantly less than anticipated (Figure ).