Spatial resolution improvement for an optical transition radiation monitor by asymmetric light collection

The applicability of optical transition radiation (OTR) for measurements of micron sized transverse electron beam profiles is limited not only by the optical system resolution which has a fundamental limit imposed by the uncertainty principle. In the case of OTR generation, a single electron crossing the boundary between vacuum and screen cannot be considered as a single emitting point with isotropic angular distribution. On the contrary, the radiation is emitted from an area with a transverse range that is defined by the radial extension of the electron's Lorentz contracted Coulomb field and is typically estimated as γλ (with γ the Lorentz factor and λ the wavelength of observation). The OTR angular distribution has a characteristic "funnel" shape. As a result the one-dimensional image of a single electron measured with an ideal thin lens has a double lobe shape, and the resolution of any OTR based imaging system is determined by this double lobe function which is also known as OTR Point Spread Function (PSF). As a consequence, the reconstruction of micron sized electron beam profiles is hampered not only due to the fundamental diffraction limit, but also due to the PSF lobe shape. In this paper we present two approaches to improve the spatial resolution of an OTR monitor based on asymmetric light collection using a traditional optical system which allows blocking of one of the lobes. With such a scheme, an OTR PSF can be achieved that is comparable to the one of an ideal point source (Airy distribution).