Ultrasensitive and high-dynamic-range two-photon absorption in a GaAs photomultiplier tube

We demonstrate improved efficiency and dynamic range for two-photon absorption at 1.5 mum. in a photoelectron-counting GaAs photomultiplier tube. cw laser measurements show pure two-photon absorption occurring in the device from average powers of 1.3 muW to nearly 1 mW. We use the detector to implement an autocorrelator with peak-power X average-power sensitivity of 1.7 X 10(-4) (mW)(2) and discuss practical ways to reduce this figure of merit to as low as 1 X 10(-5) (mW)(2). (C) 2002 Optical Society of America.