MO4C1
NTHU, Hsinchu, Taiwan
A dielectric laser accelerator, operating at optical frequencies and GHz pulse rate, is expected to produce attosecond electron bunches with a moderate beam current at high energy. For relativistic electrons, the attosecond bunch has a spatial length of a few nanometers, which is well suited for generating high-brightness superradiance in the VUV, EUV, and X-ray spectra. Our study shows that the brilliance of coherent undulator radiation driven by a short-bunch beam with 1~10 fC bunch charge from a dielectric laser accelerator is comparable to or higher than that of a synchrotron in the 0.1~3 keV photon energy range, even though the beam power of the dielectric laser accelerator is about a million times lower than that of a synchrotron. When the brilliance under comparison is normalized to the electron beam power, the proposed coherent undulator radiation source becomes the brightest source on earth across the whole VUV, EUV, and soft x-ray spectrum.
WE2C2
NTHU, Hsinchu, Taiwan
There has been a recent interest in using free electrons to interact with photonic structures and generate light. The envisaged dielectric accelerator on a chip is a low-current electron source driven by a laser. The generated electron beam contains a few electrons in each optical cycle repeating at the driver laser frequency. We perform a feasibility study in this paper on the harmonic generation of a periodic array of single electrons with keV energy atop a dielectric grating waveguide. The device is a 31 um long silicon grating on top of a glass substrate, having a 400 nm thickness and 310-nm period. The structure is designed to have a Bragg resonance at 1.5 um in wavelength or 0.2 PHz in frequency for the radiation mode. We use the simulation code CST to study the radiation from a periodic array of 25 electrons. The electrons have 50 keV energy, injected one by one at 0.1 PHz at 100 nm above the grating. The transit time of the 50 keV electrons over the 31 um long silicon grating is 0.25 ps. Cherenkov radiation is guided in the silicon waveguide layer. Smith-Purcell (SP) radiation is generated in the vacuum region above the grating. We show in simulation a ring-down of the generated coherent radiations from both ends of the grating waveguide, indicating that a grating waveguide is a good Bragg resonator. The field pattern in the waveguide region satisfies the Bragg condition, i.e. structure periodicity = half of the longitudinal wavelength. The Fourier transform of the generated radiation wave has a narrow radiation spectrum at 0.2 PHz. A discrete spectrum of SP radiation mediated by the waveguide modes is also observed from simulation in the vacuum space above the grating waveguide. This study shows the feasibility of generating harmonic radiation from a nano-photonic structure driven by keV periodic electrons.
FR1M3
NTHU, Hsinchu, Taiwan
Northern Illinois University, DeKalb, Illinois, USA