First observation of the point spread function of optical transition radiation

We represent the first experimental observation of the point spread function (PSF) of optical transition radiation (OTR) performed at KEK-Accelerator Test Facility extraction line. We have demonstrated that the PSF vertical polarization component has a central minimum with a two lobe distribution. However, the distribution width varied significantly with wavelength. We assume that we observed a severe effect from spherical or chromatic aberrations which are not taken into account in any existing theoretical model. We believe that the result of this work will encourage theoreticians to continue developing the theory as it is important for various transition radiation applications. Nonuniform distribution of the OTR PSF creates an opportunity for developing a submicrometer transverse beam size monitor.     

Feasible Design of a Free Electron Laser Based on the Smith–Parsell Effect

A free electron laser design is considered in which coherent radiation is generated during the flight of a bunched electron beam near a periodic metal target (Smith–Parsell radiation). If the target (array) is placed in a special resonator, optical feedback can be realized. It is proposed to use an array made of thin conductive strips separated with vacuum gaps, since the radiation output in this case is much higher than that attainable with conventional arrays. Varying the array parameters, one can choose the necessary direction and required spectral distribution of the Smith–Parsell radiation. When radiation is generated in the direction normal to the trajectory of the electron beam, the array acts as one of the resonator mirrors.     

Stimulated Smith-Purcell radiation

JETP Letters - The design of free-electron lasers (FELs) based on submillimeter-range undulators involves difficulties associated with the fabrication of undulators with a very small period. To do...     

A laser-wire system for the international linear collider

A new laser-wire has been installed in the extraction line of the ATF at KEK. It aims at demonstrating that laser-wires can be used to measure micrometre scale beam size. In parallel, studies have been made to specify a laser suitable for the ILC laser-wires.      

On the polarization characteristics of Cherenkov radiation from a dielectric screen

The Cherenkov effect is a well-known phenomenon and its properties are widely used in many fields of physics. However, some features of the polarization characteristics of Cherenkov radiation that appears when charged particles pass near azimuthally asymmetric, finite dielectric targets are still poorly studied. This problem is solved in this work. The polarization characteristics of Cherenkov radiation in the case of a rectangular dielectric screen are analyzed using the Stokes approach. Owing to the azimuthal asymmetry of the target, radiation acquires an elliptic polarization whose rotation direction and inclination angle depend both on the direction of radiation propagation and on the dielectric properties of a substance. The results demonstrate that the Cherenkov effect can be used to create sources of elliptically polarized radiation with the controlled direction of polarization rotation.     

Observation of subterahertz monochromatic transition radiation from a grating

Transition radiation appearing when a charged particle crosses the interface between two media with different dielectric constants, e.g., a metal–vacuum interface, has been well studied in a wide spectral range. However, primarily, radiation from smooth interfaces has been studied. Transition radiation from conducting gratings (grating transition radiation) is experimentally studied and theoretically analyzed in this work. In this case, it is possible to obtain monochromatic radiation with a tunable frequency depending on the rotation angle of the grating with respect to the electron momentum. Coherent grating transition radiation can be efficiently used as a source of terahertz radiation based on the use of a compact electron accelerator with an energy below 10 MeV and a bunch duration of ≤1 ps.     

Optical Polarization Radiation of Relativistic Electrons in Conducting Targets

A theoretical model and results of experiments on optical polarization radiation of relativistic electrons from conducting targets performed on the synchrotron and microtron of Nuclear Physics Institute at Tomsk Polytechnic University are reported. The measurements of spectral characteristics of resonance polarization radiation in periodic targets over a wide range of electron energies (both in the Smyth–Purcell geometry and for different angles between the targets and the direction of the electron beam) show reasonable agreement with theoretical estimates.     

Stability of colliding flows

The stability of the flow in the interaction region of colliding streams is investigated in the framework of linear theory. To simplify the analysis, the treatment is restricted to the case of an ideal fluid and an irrotational main flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti Gaza, No. 5, pp. 143–147, September–October, 1981.