Laser Design for Next Generation Compton Scattering Source at LLNL

We describe laser systems designed for the next generation Mono-Energetic Gamma-Ray (MEGa-ray) Compton scattering light source at LLNL. An 80 fs Yb:doped fiber oscillator seeds a photogun drive laser (PDL) and a high energy interaction system laser (ILS). Utilizing chirped pulse amplification (CPA) in fiber, the PDL will generate 80 $\mu $J, spatially and temporally shaped pulses at 263 nm at 120 Hz precisely synchronized to the linac RF. The PDL system employs large mode photonic bandgap fibers and large area multi-layer dielectric gratings to generate over 1mJ per pulse with high recompression fidelity prior to frequency quadrupling. The high energy, 120 W ILS utilizes (CPA) in Nd:YAG to amplify a sub-nanometer bandwidth 20 $\mu $J pulses from a fiber system to 1 J. A novel pulse stretcher provides a dispersion of over 7000 ps/nm to expand a several picosecond wide seed pulse to 6 ns. After amplification, the pulse is recompressed to 10 ps with a hyper-dispersive pulse compressor. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.