The optical transition radiation emitted by electron‐irradiated aluminum, silver, gold‐coated plates, and self‐supported aluminum and Mylar films has been investigated experimentally. The investigation was made with an electron beam incident at 45 °, having a mean intensity of 1 μA, and an energy which was varied from 35 up to 72 MeV (68.5<γ<140.9). The study of the angular distribution and degree of polarization has shown that the high‐directivity radiation is emitted around the direction of specular reflection and that the contribution of the optical bremsstrahlung is negligible. When two parallel foils are used, the resulting angular distribution exhibits an oscillating behavior arising from the interference of the fields emitted at both interfaces. This interference phenomenon is strongly related to the so‐called formation zone in a vacuum, introduced by Garibyan. The intensity of light integrated in a small aperture at the center of the interference pattern presents a strong γ dependence (of the form γ8) which was exploited in the optimization of the phase adjustment of the electron bunches in the accelerating sections of the machine. In such a device using the interference phenomena in transition radiation, the possibility of measurements of the beam energy with a precision of about 1% has also been shown. On the basis of the visibility of fringes, the angular spread of the electron beam and the mean‐square scattering angle in a given material were also estimated.

Interference phenomenon in optical transition radiation and its application to particle beam diagnostics and multiple‐scattering measurements

Plasma-based accelerators that impart energy gain as high as several GeV to electrons or positrons within a few centimeters have engendered a new class of diagnostic techniques very different from those used in connection with conventional radio-frequency (rf) accelerators. The need for new diagnostics stems from the micrometer scale and transient, dynamic structure of plasma accelerators, which contrasts with the meter scale and static structure of conventional accelerators. Because of this micrometer source size, plasma-accelerated electron bunches can emerge with smaller normalized transverse emittance (en<0.1  mm mrad) and shorter duration (τb∼1  fs) than bunches from rf linacs. Single-shot diagnostics are reviewed that determine such small en and τb noninvasively and with high resolution from wide-bandwidth spectral measurement of electromagnetic radiation the electrons emit: en from x rays emitted as electrons interact with transverse internal fields of the plasma accelerator or with external optical fields or undulators; τb from THz to optical coherent transition radiation emitted upon traversing interfaces. The duration of ∼1  fs bunches can also be measured by sampling individual cycles of a copropagating optical pulse or by measuring the associated magnetic field using a transverse probe pulse. Because of their luminal velocity and micrometer size, the evolving structure of plasma accelerators, the key determinant of accelerator performance, is exceptionally challenging to visualize in the laboratory. Here a new generation of laboratory diagnostics is reviewed that yield snapshots, or even movies, of laser- and particle-beam-generated plasma accelerator structures based on their phase modulation or deflection of femtosecond electromagnetic or electron probe pulses. Spatiotemporal resolution limits of these imaging techniques are discussed, along with insight into plasma-based acceleration physics that has emerged from analyzing the images and comparing them to simulated plasma structures.

/pdf/diagnostics-for-plasma-based-electron-accelerators-cnmw8siriq.pdf

Diagnostics for plasma-based electron accelerators

The characteristics of diffraction radiation (DR), i.e. radiation of the charged particle moving near conducting target have been considered for an ultrarelativistic case. The simple expressions for DR fields for the semi-infinite ideal conducting target have been derived. The close connection between transition radiation (TR) and DR has been shown. The effect of finite transversal sizes of target on TR characteristics has been evaluated.

Transition radiation and diffraction radiation. Similarities and differences

Transition radiation from a beam of hot electrons generated in ultraintense laser plasma interaction is theoretically studied. The total radiation is separated into two parts: one is incoherent transition radiation (ITR), the other is coherent transition radiation (CTR). The spectrum of ITR just depends on the particle velocity distribution in the beam. The angular distribution of ITR varies from sin2 θ, and approaches the angular distribution of the beam when the hot electron temperature increases from the nonrelativistic limit (T≪mc2) to the ultrarelativistic limit (T≫mc2). The spectrum of CTR is dependent on the particle configuration as well as their velocities. Any microbunching in the beam can greatly enhance the CTR intensity at the microbunching frequency, from which the dominant heating process can be inferred. The effects of target thickness and hot electron temperature on CTR intensity are also calculated. The simplified model shows that the CTR intensity decreases with the increase of the targ...

/pdf/theoretical-study-of-transition-radiation-from-hot-electrons-4iim6kgppf.pdf

Theoretical study of transition radiation from hot electrons generated in the laser–solid interaction

Investigating the interaction of electron beams with materials and light has been a field of research since more than a century. The field was advanced theoretically by the raise of quantum mechanics and technically by the introduction of electron microscopes and accelerators. It is possible nowadays to uncover a multitude of information from electron-induced excitations in matter by means of advanced techniques like holography, tomography, and most recently photon-induced near-field electron microscopy. The question is whether the interaction can be controlled in an even more efficient way in order to unravel important questions like modal decomposition of the electron-induced polarization, by performing experiments with better spatial, temporal, and energy resolutions. This review discusses recent advances in controlling the electron and light interactions at the nanoscale. Theoretical and numerical aspects of the interaction of electrons with nanostructures and metamaterials will be discussed, with the aim to understand mechanisms of radiation in interaction of electrons with even more sophisticated structures.

https://iopscience.iop.org/article/10.1088/2040-8986/aa8041/pdf

Interaction of electron beams with optical nanostructures and metamaterials: from coherent photon sources towards shaping the wave function

Optical transition radiation produced by 40-60 MeV electrons crossing thin metallic foils has been studied in order to provide a beam diagnostic device. The radiation yield is roughly one photon per 100 electrons and the intensity appears to be Z independent ; the influence of bremsstrahlung is then fairly weak. Measurements of angular and ? dependence, spectral density and polarisation have been carried out and results are in good agreement with theories. When multiple scattering angles are negligible (< ?-1), a strong eneray dependence, close to ?3 , of the light intensity radiated into small solid angles is found. Moreover, the radiation is peaked in a direction making an angle ?-1 with the beam axis. Suitable optical arrangement make it possible beam position and profile determination. Measurement of the polarisation plane rotation by means of a scanning mirror provides a method of determining the incident angle of the beam onto the target. This device looks promising for diagnostics on particle beams-electrons as well as protons-with normalized energies ? in the range 1-103.

Detection of Optical Transition Radiation and Its Application to Beam Diagnostics

Rayonnement de transition dans le domaine optique, produit par des électrons de 40–60 MeV à la traversée de lames métalliques

Th optical transitionradiatio emitted by electron irradiated aluminum, silver, gold-coated plates and self-supported metallic and mylar films has been investigated experimental ly using 450 incident electron beams with intensities°from 100 pA up to 10 , A, and energies from 35 up to 72 MeV. Beam d?gnostics (intensity, profile, centering, energy) were made using an ppropriae optical rrangment together with a two-parallel foilsdevice in which the interference phenomena in transiti. on radiation emitted at both interfaces was exploited. The intensity of light integrated in a small aperture at the center of the interference pattern presents a strong particle-energy dependence(of the form. sE8) which was used in the optimization of the p~a8e adjustment of the electron bunches in the linac at small current intensities. Moreover, study of the visibility of fringes yields to an estimate of the transverse mo-mentum spread of the electron beam and to he r. m. s. angle of multiple scattering in a given mteial.

https://epaper.kek.jp/p75/pdf/pac1975_1552.pdf

S. Roland

Papers

Interference phenomenon in optical transition radiation and its application to particle beam diagnostics and multiple‐scattering measurements

Detection of Optical Transition Radiation and Its Application to Beam Diagnostics

Rayonnement de transition dans le domaine optique, produit par des électrons de 40–60 MeV à la traversée de lames métalliques

Thin Films on LINAC Beams as Non-Destructive Devices for Particle Beam Intenstty, Profile, Centertng and Energy Monitors