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Tomizawa, H. T.

Paper Title Page
WEBAU01 Adaptive 3-D UV-laser Pulse Shaping System to Minimize Emittance for Photocathode RF Gun 298
 
  • T. Asaka, H. Dewa, H. Hanaki, T. Kobayashi, A. Mizuno, S. Suzuki, T. Taniuchi, K. Yanagida, H. T. Tomizawa
    JASRI/SPring-8, Hyogo-ken
  • F. Matsui
    Industrial Technology Center of Fukui, Fukui City
 
  We developed an adaptive 3-D shaping (both temporal (1D) and spatial (2D)) short pulse (80 fs~40 ps) UV-laser system as an ideal light source for yearlong stable generation of a low emittance electron beam with a high charge (1~2 nC/pulse). In its current form, the laser’s pulse-energy stability has been improved to 0.2~0.3% (rms; 10 pps, 0.4 TW in femtosecond operation) at the fundamental wavelength and 0.7~1.4% at the third-harmonic generation. Such improvement reflects an ability to stabilize the laser system in a humidity-controlled clean room. The pulse-energy stability of a mode-locked femtosecond oscillator has been continuously held to 0.3% (p-p) for 10 months, 24 hours a day. In addition, the ideal spatial and temporal profiles of a shot-by-shot single UV-laser pulse are essential to suppress emittance growth in an RF gun. We apply a deformable mirror that automatically shapes the spatial UV-laser profile with a feedback routine, based on a genetic algorithm, and a pulse stacker for temporal shaping at the same time. The 3D shape of the laser pulse is spatially top-hat (flattop) and temporally a square stacked pulse. Using a 3D-shaped laser pulse with a diameter of 0.8 mm on the cathode and pulse duration of 10 ps (FWHM), we obtain a minimum normalized emittance of 1.4 π mm mrad with beam energy of 26 MeV.  
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WEPPH022 Feasibility Test of Shottoky Effect-Gated Photocathode RF Gun 382
 
  • M. Kobayashi
    Nanophoton corporation, Osaka
  • H. T. Tomizawa
    JASRI/SPring-8, Hyogo-ken
 
  We proposed Shottoky effect-gated photocathode RF gun using z-polarization of laser source. Radically polarized laser propagation modes exist theoretically and were recently generated practically. Focusing a radically polarized beam on the photocathode, the z-polarization of laser is generated at the focusing point. The generated Z-polarization can exceed an electrical field of 1GV/m easily with fundamental wavelength from compact femtosecond laser systems. According to our calculations, the z-field of 1GV/m needs 100MW at peak power for fundamental wavelength (790nm) and 25MW for SHG. In the field of 1GV/m, the work function of copper cathode reduces ~2 eV. The quantum efficiency will be ~10-4 at SHG by the Shottoky effect associated with the 1GV/m. This Shottky effect can be used as a gate of photo-emission process. In our design of Shottoky effect-gated Photocathode, the fundamental is used as gate pulse and SHG as laser source for photo-emission process. The same single laser pulse can also gate its emission by itself. To keep normal incidence on the cathode, we developed modified-Cessegrain-type incident optics combining with axicon lens pair. In the first test run, we are preparing z-polarizer for SHG to generate radial and azimuth polarizations. Comparing photo-emission process with these polarizations, we make clear the feasibility of this new concept of photocathode.  
WEPPH053 Non-Destructive Single-Shot 3-D Electron Bunch Monitor with Femtosecond-Timing All-Optical System for Pump & Probe Experiments 472
 
  • H. Hanaki, H. T. Tomizawa
    JASRI/SPring-8, Hyogo-ken
  • T. Ishikawa
    RIKEN Spring-8 Harima, Hyogo
 
  We are developing a 3-D electron bunch monitor based on EO sampling, using yearlong stable femtosecond laser source of SPring-8 RF gun. Our developing single-shot bunch monitor can characterize the 3-D (both longitudinal (1D) and transverse (2D)) distribution and position of an electron bunch with femtosecond resolution. This non-destructive monitor can be used as an electron energy chirping monitor in a dispersive region for X-FEL commissioning. The probe laser for spectral decoding EO sampling is prepared as radically polarized and completely linearly chirped broad-bandwidth (~500nm) supercontinuum. EO-probe is made of 8 EO-crystals with assembling each EO-optical axes along radial beam axes. The probe lineally chirped laser is longitudinally sifted in 8 transverse sectors for spectral decoding. We are planning to use organic polymer film as a femtosecond resolution EO-probe instead of crystals. This 3-D bunch monitor with spectrograph detects and analyzes the wake filed of electron bunches as longitudinally spectral decoding and transversely multi-pole expansion. In addition, we are developing all-optical system for femtosecond-timing pump & probe experiments. The EO-sampled probe laser pulse will use as a femtosecond-timing signal pulse. This signal pulse is amplified with a NOPA (noncollinear optical parametric amplifier), using an SHG of Yb fiber laser as a pump laser.