Phenomenological model for mixed multiphoton absorption in bialkali photocathode and application to ultrafast pulse characterization

摘要

We propose a phenomenological model composed of concise formulas to describe mixed multiphoton absorption (MPA), revealing its quasi-exponent-function in relation to intensity, complicated spectral features, and polarization dependence, and then demonstrate it perfectly by experiments on a bialkali-cathode photomultiplier-tube (PMT) single-photon detector. The dichroism parameter is obtained based on polarization dependent visibility. Accomplishing MPA-based autocorrelation, we manifest that the peak-to-baseline contrast ratio is determined by the mixture exponent. After extracting the pure two-photon absorption, we obtain the ultrafast pulse width which agrees well with that of the standard autocorrelator. Furthermore, we put forward the mutual-correlation scheme and acquire accurately the time jitter of a femtosecond-pulse train. Our results pave the way for analyzing high-order complex MPAs and characterization of ultrafast pulses with super accuracy by a widely used bialkali PMT.