Table-top SuperRadiant Free Electron Laser

Table-top SuperRadiant Free Electron Laser, Coherent Harmonic Generation with Deep Energy Modulation.Figure 1: Focal spot of the seed laser, located near the middle of the modulator and Interference fringe pattern between the seed laser and the main laser, measured near the middle of the modulator. Figure 2: Measured and simulated spectra of the accelerated e beam and the corresponding longitudinal phase spaces of the e beam. (a) and (b) Typical shots for the e-beam spectra with the seed laser off and on, measured by the spectrometer locates at 4.5 m from the gas target. (c) and (d) Simulated spectra of the e beam at the location of the spectrometer with the seed laser off and on. (e) and (f) Simulated longitudinal phase spaces of the e beam at the entrance of the radiator. Figure 3: Properties of the coherent radiation with central wavelengths of approximately 380 nm and 255 nm. (a) and (b) Three typical shots for the coherent radiation with a central wavelength of approximately 380 nm and 255 nm, respectively. (c) and (d) Measured backgrounds over 20 shots with only the seed laser off. (e) and (f) Simulated spectra of the coherent radiation with the parameters matches with the experimental condition. (g) and (h) Integral spectra of the experimental and simulated results. Figure 4: Quadratic Charge Dependence of the FEL Radiation. Charge of the accelerated e beam versus the measured counts of the radiation at the exit of the beamline. ExtendedData_Fig1: Properties of the laser. (a) The near field profile of the main laser, with a small fraction split off as the seed laser. (b) The focal spot of the main laser pulse after splitting a small fraction as the seed laser. ExtendedData_Fig2: Snapshots of the simulation results at various longitudinal positions. The on-axis accelerating field, the longitudinal phase space of the accelerated electrons, and the density map of the electrons.ExtendedData_Fig3: (a) and (b) Longitudinal phase space distribution of the accelerated e beam obtained from the FBPIC code (a) and after up-sampling (b). A joint cumulative distribution function was employed to up-sample the number of macroparticles in 3D from an initial value of 13.8 k to 4.7 million. (c) and (d) The current (c) and slice energy spread (d) along the beam for the initial (black solid line) and up-sampled (blue solid line) e beam. (e-h) Transverse phase space distributions of the accelerated e beam before (e and g) and after up-sampling (f and h). ExtendedData_Fig4: (a) The layout of the beamline and the evolution of the e-beam size (root mean square, RMS) along the beam line. The red, green and blue squares represent quadruples, modulator and radiator, respectively. (b) and (c) Simulated longitudinal phase space distributions at the entrance of the radiator for the situations without seeding (b) and with seeding (c). (d)The bunching factor as a function of the radiation wavelength for the situations without seeding and with seeding. ExtendedData_Fig5: Properties of the e-beam spectra and the corresponding coherent radiation with the central wavelength of approximately 380 nm.