Search for: All records

Abstract Free-electron-lasers fill a critical gap in the space of THz-sources as they can reach high average and peak powers with spectral tunability. Using a waveguide in a THz FEL significantly increases the coupling between the relativistic electrons and electromagnetic field enabling large amounts of radiation to be generated in a single passage of electrons through the undulator. In addition to transversely confining the radiation, the dispersive properties of the waveguide critically affect the velocity and slippage of the radiation pulse which determine the central frequency and bandwidth of the generated radiation. In this paper, we characterize the spectral properties of a compact waveguide THz FEL including simultaneous lasing at two different frequencies and demonstrating tuning of the radiation wavelength in the high frequency branch by varying the beam energy and ensuring that the electrons injected into the undulator are prebunched on the scale of the resonant radiation wavelength. 

Abstract Advances in ultrafast laser technology and nanofabrication have enabled a new class of particle accelerator based upon miniaturized laser-driven photonic structures. However, developing a useful accelerator based on this approach requires control of the particle dynamics at field intensities approaching the damage limit. We measure acceleration in a fused silica dielectric laser accelerator driven by fields of up to 9 GV m⁻¹and observe a record 1.8 GV m⁻¹in the accelerating mode. At these intensities the dielectric is driven beyond its linear response and self-phase modulation changes the phase velocity of the accelerating mode, reducing the average gradient to 850 MeV m⁻¹. We show that free-space optics can be used to compensate this dephasing and demonstrate that tailoring the laser phase and amplitude can facilitate optimization of the beam dynamics. This could enable MeV scale energy gain in a single stage and pave the way towards applications in scientific, industrial, and medical fields. 

The development of long, tunable structures is critical to increasing energy gain in laser-driven dielectric accelerators (DLAs). Here we combine pulse-front-tilt illumination with slab-geometry structures assembled by precisely aligning off-the-shelf 4 mm long transmission gratings to achieve up to 200 keV energy modulation for 6 MeV injected electrons. The effective interaction length is longer than 1 mm, limited by the dephasing of the accelerated particles in the structure. The piezo-based independent mounting system for the gratings allows tuning of the gap and field distribution inside the structure. Published by the American Physical Society2024 

Extremely high beam-to-radiation energy conversion efficiencies can be obtained in a THz FEL using a strongly tapered helical undulator at the zero-slippage resonant condition, where a circular waveguide is used to match the radiation group velocity to the electron beam longitudinal velocity. In this paper we report on the first electro-optic sampling (EOS) based measurements of the broadband THz FEL radiation pulses emitted in this regime. The THz field waveforms are reconstructed in the spatial and temporal domains using multi-shot and single-shot EOS schemes respectively. The measurements are performed varying the input electron beam energy in the undulator providing insights on the complex dynamics in a waveguide FEL. 

Abstract We discuss recent developments and challenges of beam dynamics in Dielectric Laser Acceleration (DLA), for both high and low energy electron beams. Starting from ultra-low emittance nanotip sources the paper follows the beam path of a tentative DLA light source concept. Acceleration in conjuction with focusing is discussed in the framework of Alternating Phase Focusing (APF) and spatial harmonic ponderomotive focusing. The paper concludes with an outlook to the beam dynamics in laser driven nanophotonic undulators, based on tilted DLA grating structures. 

Dielectric laser accelerators (DLAs) are fundamentally based on the interaction of photons with free electrons, where energy and momentum conservation are satisfied by mediation of a nanostructure. In this scheme, the photonic nanostructure induces near-fields which transfer energy from the photon to the electron, similar to the inverse-Smith–Purcell effect described in metallic gratings. This, in turn, may provide ground-breaking applications, as it is a technology promising to miniaturize particle accelerators down to the chip scale. This fundamental interaction can also be used to study and demonstrate quantum photon-electron phenomena. The spontaneous and stimulated Smith–Purcell effect and the photon-induced near-field electron-microscopy (PINEM) effect have evolved to be a fruitful ground for observing quantum effects. In particular, the energy spectrum of the free electron has been shown to have discrete energy peaks, spaced with the interacting photon energy. This energy spectrum is correlated to the photon statistics and number of photon exchanges that took place during the interaction. We give an overview of DLA and PINEM physics with a focus on electron phase-space manipulation.