Numerical analysis of two-dimensional fitting of the electron beam divergence angle in optical transition radiation

The optical transition radiation (OTR) shows a distinct directional property with respect to the incident charged particle. The beam divergence angle can be measured by curve fitting of the OTR spatial distribution. The method of theoretical calculation is used to analyze the impact of the variation of the incident angle on the two-dimensional spatial distribution of the OTR when the electron incidents at the metal-dielectric boundary. Theoretical calculations indicate that the OTR distribution in a specific polarization is determined not only by the divergence angle component in the polarization direction but also by that in the perpendicular direction. The difference between the OTR distributions based on one-dimensional modeling and two-dimensional modeling of the divergence angle of the electron beam is calculated. It is demonstrated that the RMS divergence angle of the electron beam based on one-dimensional modeling is generally smaller than that based on two-dimensional modeling.