Characterization of ultra-intense laser in radiation damping regime using ponderomotive scattering

We present a novel approach to analyzing phase-space distributions of electrons ponderomotively scattered off an ultra-intense laser pulse and comment on implications for thus conceivable in-situ laser-characterization schemes. To this end, we present fully relativistic test particle simulations of electrons scattered from an ultra-intense, counter-propagating laser pulse. The simulations unveil non-trivial scalings of the scattered electron distribution with the laser intensity, pulse duration, beam waist, and energy of the electron bunch. We quantify the found scalings by means of an analytical expression for the scattering angle of an electron bunch ponderomotively scattered from a counter-propagating, ultra-intense laser pulse, also accounting for radiation reaction (RR) through the Landau-Lifshitz (LL) model. For various laser and bunch parameters, the derived formula is in excellent quantitative agreement with the simulations. We also demonstrate how in the radiation-dominated regime a simple re-scaling of our model's input parameter yields quantitative agreement with numerical simulations based on the LL model.

Peak Shift of Coherent Edge Radiation Spectrum Depending on Radio Frequency Field Phase of Accelerator

Spectra of coherent edge radiation (CER) were observed at the S-band linac facility of Kyoto University Free Electron Laser. A local maximum was observed in the CER spectrum on-crest operation of the radio frequency (RF) field. As the phase of the RF field was shifted from the crest, the frequency of the maximum decreased, and the CER spectrum approached a spectrum of Gaussian-distributed electrons in a bunch. It was found that this strange spectrum can be explained by a model in which a satellite pulse exists around a main pulse in the electron bunch. Furthermore, it demonstrated that CER is an effective tool for monitoring the shape of the electron bunch.

TRANSITION RADIATION OF A RELATIVISTIC ELECTRON BUNCH ON A SEMI-INFINITE METAL CYLINDER

Transition radiation of a relativistic electron bunch, which arises when it collides with the end face of a semi-infinite ideally conducting cylinder, is considered. An electron bunch moves along the axis of a semi-infinite cylin-der. Expressions for the field strength of electromagnetic radiation in the wave zone are obtained. The influence of the guiding properties of an ideally conducting cylinder on the directional diagram of the transition radiation is investigated.

Real-time ultrafast oscilloscope with a relativistic electron bunch train

The deflection of charged particles is an intuitive way to visualize an electromagnetic oscillation of coherent light. Here, we present a real-time ultrafast oscilloscope for time-frozen visualization of a terahertz (THz) optical wave by probing light-driven motion of relativistic electrons. We found the unique condition of subwavelength metal slit waveguide for preserving the distortion-free optical waveform during its propagation. Momentary stamping of the wave, transversely travelling inside a metal slit, on an ultrashort wide electron bunch enables the single-shot recording of an ultrafast optical waveform. As a proof-of-concept experiment, we successfully demonstrated to capture the entire field oscillation of a THz pulse with a sampling rate of 75.7 TS/s. Owing to the use of transversely-wide and longitudinally-short electron bunch and transversely travelling wave, the proposed “single-shot oscilloscope” will open up new avenue for developing the real-time petahertz (PHz) metrology.

Radioluminescence Response of Ce-, Cu-, and Gd-Doped Silica Glasses for Dosimetry of Pulsed Electron Beams

Radiation-induced emission of doped sol-gel silica glass samples was investigated under a pulsed 20-MeV electron beam. The studied samples were drawn rods doped with cerium, copper, or gadolinium ions, which were connected to multimode pure-silica core fibers to transport the induced luminescence from the irradiation area to a signal readout system. The luminescence pulses in the samples induced by the electron bunches were studied as a function of deposited dose per electron bunch. All the investigated samples were found to have a linear response in terms of luminescence as a function of electron bunch sizes between 10−5 Gy/bunch and 1.5×10−2 Gy/bunch. The presented results show that these types of doped silica rods can be used for monitoring a pulsed electron beam, as well as to evaluate the dose deposited by the individual electron bunches. The electron accelerator used in the experiment was a medical type used for radiation therapy treatments, and these silica rod samples show high potential for dosimetry in radiotherapy contexts.

Generation in the regime with three resonance frequencies

If the group velocity of the wave is close to the bunch velocity, the bunch placed in the maximumum of the radiated pulse. It provides high effeciency of the electron-wave interaction. However, there are other factors related to particle dynamics, which have strong influence on the radiation process. In this paper the regime with three resonance frequencies is discussed. By varying the phase size of the electron bunch, the generation conditions at each of the frequencies can be changed. There are results for the spontaneous coherent super-radiative undulator emission in the terahertz frequency range from a short (as compared to the wavelength of the radiated wave) dense electron bunch. As a result, an electron bunch radiates two pulses with amplitudes of the radiated fields ∼ 10-70 MV/m.

Generation of ultrashort pulses in the THz frequency range

There are results for the spontaneous coherent super-radiative undulator emission in the terahertz frequency range from a short (as compared to the wavelength of the radiated wave) dense electron bunch. If the group velocity of the wave is close to the bunch velocity, this is a process of spontaneous radiation followed by amplification of a single wave cycle. Despite the Coulomb repulsion of electrons inside the bunch, its compactness is provided by the compression of the bunch under the action of its own radiation fields. As a result, formation of an ultra-short (several cycles long) powerful wave packet occurs when the bunch moves through several undulator periods with high (∼20% in optimized systems) efficiency of extraction of the electron energy and high intensity (∼ 100 MV/m) of the peak wave field.

A synchrotron-based kilowatt-level radiation source for EUV lithography

A compact damping ring with limited circumference of about 160 m is proposed for producing kilowatt-level coherent EUV radiation. The electron bunch in the ring is modulated by a 257nm wavelength laser with the help of the angular dispersion induced micro-bunching method [C. Feng and Z. Zhao, Sci. Rep. 7, 4724 (2017)]. Coherent radiation at 13.5 nm with an average power of about 2.5 kW can be achieved with the state-of-the-art accelerator and laser technologies.