Very high resolution optical transition radiation imaging system: Comparison between simulation and experiment

Abstract

Optical transition radiation (OTR) has become a commonly used method for 2D beam imaging measurements. In the Accelerator Test Facility 2 (ATF2) at KEK, beam sizes smaller than the OTR point spread function have been measured. Simulations of the OTR imaging system have been performed using the ZEMAX software to study the effects of optical errors such as aberrations, diffraction, and misalignments of optical components. This paper presents a comparison of simulations of the OTR point spread function with experimental data obtained at ATF2. It shows how the quantification and control of optical errors impacts on optimizing the resolution of the system. We also show that the OTR point spread function needs to be predicted accurately to optimize any optical system and to predict the error made on measurement.

Generation and measurement of sub-micrometer relativistic electron beams

“…The spatial resolution of optical transition radiation screens (OTRs) is only limited by the camera sensor and optics [13]. In the Accelerator Test Facility 2 at KEK, a vertical beam size of 750 nm has been measured by means of OTR monitors [24,25]. Nevertheless, OTRs are limited by the emission of coherent optical transition radiation from compressed bunches, which prevents their usage in FELs [26].…”

Experimental Observation of “Shadowing” in Optical Transition Radiation

“…At a distance δ ≫ 1, the electron field will be completely restored to its original value and is completely separated with the FTR field. The validity of a purely optical model for shadowing is further confirmed by optical simulations, performed with Zemax OpticStudio [25,26], of the propagation of the forward OTR field from the first screen to the second one using near-field diffraction formulas. The resulting field is overlapped with the backward OTR field generated by the beam at the input face of the second screen.…”

Simulation of transition radiation based beam imaging from tilted targets

“…The authors in Ref. [22] call this region a "blind area" where a beam size determination does not seem to be possible with any of the existing approaches.…”

“…The fit was performed for vertical cuts at different horizontal positions in the image (x i ¼ 0, x i =M ¼ 10 μm, x i =M ¼ 20 μm), and following Ref. [22] the profile from the central position corresponds to the situation of data analysis in the blind zone. Figure 10 shows the comparison for the SPF dominated beam image, calculated for θ m ¼ 0.19, λ ¼ 400 nm, and σ y ¼ 1 μm, together with the associated profile fits.…”

“…Using existing OTR SPF models which are based on axial symmetry in the observation geometry the banana-shaped beam images could not be explained, and instead numerical simulations were carried out based on commercial ray tracing software [22]. Such numerical simulations are a powerful tool but may conceal the underlying physical processes.…”