"Coherent and incoherent cathodoluminescence photon statistics"

Abstract:

Recent CL studies using Hanbury-Brown=Twiss interferometry uncovered unexpectedly strong photon bunching behavior in the g⁽²⁾(τ) measurement, meaning that CL photons excited by CW electron beams show apparent super-Poissonian statistics. This CL photon bunching can be understood through the mixture with zero photon states introduced by random electron excitation with some intervals. While such bunching behavior is useful to measure the emission lifetime, it blurs the “true” photon statistics by free electron excitation.

We here extract the photon statistics within the single electron excitation event by comparing the “bunching” and the flat background parts in the g⁽²⁾(τ) curves. This allows calculating a parameter corresponding to g⁽²⁾(0) in the single electron excitation, which we call the correlation factor κ_corr. In coherent CL processes, where light is generated through a direct electromagnetic interaction, κ_corr is found to be ~1 in various coherent CL systems. This confirms that coherent CL obeys Poisson statistics, in agreement with the coherent states.  However, in incoherent CL, which involves multiple mediator particle generations (like bulk plasmons or secondary electrons, Fig.1d), κ_corr exceeds 1, meaning that incoherent CL is super-Poissonian (“bunching”) even within the single excitation event.

Through a model analysis with multiple (cascade) particle generation steps, we were able to reproduce this super-Poissonian behavior in incoherent CL even when each particle generation process follows Poissonian statistics. This approach not only offers a refined understanding of CL mechanisms but can also be extended to the analysis of internal particle generation processes in general.