Speaker
Description
Recently, super-bunching ($g^{(2)}(\tau)>2$) has been experimentally observed in cathodoluminescence (CL) photon-correlation measurements and used to analyze luminescence dynamics [1]. This bunching behavior originates from both external and internal factors: temporal fluctuations in electron arrival and the inherent photon statistics generated by individual excitation events. In this work, we propose a method to extract the inherent photon statistics eliminating the effect of the electron beam fluctuation affect [2].
We investigated CL photon correlations using a Hanbury Brown–Twiss (HBT) interferometer integrated into a STEM-CL system. The intrinsic photon statistics, or the correlation factor $\kappa_{corr}$, was evaluated for coherent and incoherent CL, which have direct (single) and indirect (multiple) excitation processes, respectively. For coherent CL, $\kappa_{corr}$ was found approximately unity, indicating that photons are generated through a single interaction event following the Poisson statistics. In contrast, for incoherent CL, $\kappa_{corr} > 1$, corresponding to super-Poissonian statistics, even after eliminating the modulation effect by incident electrons. This super-Poissonian behavior can be described by a model based on a cascade excitation process, in which a single incident electron generates intermediate particles that subsequently produce multiple photons. Our model suggests that the value of $\kappa_{corr}$ directly reflects the number of intermediate particles. Through thickness-dependent measurements of luminescent materials, we observed systematic changes in $\kappa_{\mathrm{corr}}$ and experimentally estimated the number of intermediate particles generated by a single incident electron. This work establishes a quantitative method for evaluating cascade reactions and provides insight into the fundamental mechanisms of light emission induced by fast electron beams.
[1] MEURET, Sophie, et al. Photon bunching in cathodoluminescence. Physical review letters, 2015, 114.19: 197401.
[2] YANAGIMOTO, Sotatsu, et al. Unveiling the nature of cathodoluminescence from photon statistics. Communications Physics, 2025, 8.1: 56.