Coherent Cherenkov radiation as an intense THz source

Diffraction and Cherenkov radiation of relativistic electrons from a dielectric target has been proposed as mechanism for production of intense terahertz (THz) radiation. The use of an extremely short high-energy electron beam of a 4th generation light source (X-ray free electron laser) appears to be very promising. A moderate power from the electron beam can be extracted and converted into THz radiation with nearly zero absorption losses. The initial experiment on THz observation will be performed at CLARA/VELA FEL test facility in the UK to demonstrate the principle to a wider community and to develop the radiator prototype. In this paper, we present our theoretical predictions (based on the approach of polarization currents), which provides the basis for interpreting the future experimental measurements. We will also present our hardware design and discuss a plan of the future experiment

Generation of incoherent Cherenkov diffraction radiation in synchrotrons

Incoherent Cherenkov diffraction radiation was recently produced in the Cornell electron storage ring using counterpropagating beams (electrons and positrons) passing in the close vicinity of a dielectric made of fused silica. We present in this paper a collection of the experimental investigations that were performed on Cherenkov diffraction radiation in both the infrared and the visible range. Measurements were performed using an optical system functioning either in imaging conditions or in far field conditions to retrieve the angular distribution of the radiation. Polarization studies were also performed and showed that, when selecting the appropriate polarization, the beam size can be measured accurately. This study opens the path for new applications in noninvasive beam diagnostic for highly relativistic charged particle beams

Direct Observation of Incoherent Cherenkov Diffraction Radiation in the Visible Range

We report on the observation of incoherent Cherenkov radiation emitted by a 5.3 GeV positron beam circulating in the Cornell electron-positron storage ring as the beam passes in the close vicinity of the surface of a fused silica radiator (i.e., at a distance larger than 0.8 mm). The shape of the radiator was designed in order to send the Cherenkov photons towards the detector, consisting of a compact optical system equipped with an intensified camera. The optical system allows both the measurements of 2D images and angular distribution including polarization study. The corresponding light intensity has been measured as a function of the distance between the beam and the surface of the radiator and has shown a good agreement with theoretical predictions. For highly relativistic particles, a large amount of incoherent radiation is produced in a wide spectral range. A light yield of $0.8 \times 10^{−3}$ photon per particle per turn has been measured at a wavelength of $600 \pm 10$  nm in a 2 cm long radiator and for an impact parameter of 1 mm. This will find applications in accelerators as noninvasive beam diagnostics for both leptons and hadrons