Two-photon cross-section measurements using an optical chopper: z-scan and two-photon fluorescence schemes

An effective z-scan setup with a minimum thermal effect is shown for intensity-dependent measure of two-photon absorption (TPA) with high-repetition rate lasers. Use of an additional intensity modulation with an optical chopper provides enough blanking time for a high-repetition rate laser to yield equally accurate results in TPA measurements compared to a low repetition laser. Extension of this method of thermal effect management with an optical chopper to emission studies also results in good correspondence for two-photon cross-section measurements from either z-scan or two-photon fluorescence techniques. The method also significantly enhances two-photon fluorescence, which could be promising for multiphoton microscopy.