Experimental Observation of “Shadowing” in Optical Transition Radiation

Abstract

We report the observation of shadowing between two optical transition radiation (OTR) sources from a 205 MeV electron beam. The total optical intensity is measured as a function of the distance d between the sources, covering the range 0 < d < 4L v , where L v is the formation length of the particles. Data show that the total optical intensity starts decreasing due to shadowing when d approaches L v until it becomes undetectable for very short distances d/L v → 0. A model based solely on interference between the two OTR sources is in good agreement with experimental data. To the knowledge of the authors this is the first systematic experimental observation of shadowing in OTR.

Noninvasive Micrometer-Scale Particle-Beam Size Measurement Using Optical Diffraction Radiation in the Ultraviolet Wavelength Range

“…The distance between the mask and the target ("dist") is 123 mm. Considering the wavelength (λ) observed during the experiment, this distance represents a fraction of the radiation formation zone (L f = γ 2 λ/2π ); in particular, dist ≈ 0.3L f for λ = 400 nm and dist ≈ 0.48L f for λ = 250 nm [18,26], meaning that interference between the diffraction radiation produced from the mask and from the target must be taken into account in the analysis, as shown in Ref. [18].…”