LLE Review 134

Review 134


This volume of the LLE Review, covering January–March 2013, features "Commissioning of a Multiple-Frequency-Modulation Smoothing by Spectral Dispersion Demonstration System on OMEGA EP," which describes the performance of OMEGA EP seeded by optical pulses with high-frequency phase modulations. This demonstration includes angular dispersion by a diffraction grating, propagation and amplification in a NIF preamplifier module and one OMEGA EP beamline, frequency conversion, and beam smoothing after a distributed phase plate and focusing. Laser operation is characterized in conditions relevant to an implementation of multi-FM beam smoothing on the NIF to support polar drive.

Additional highlights of research presented in this issue include the following:

  • Modeling and simulation results describing the propagation of spatially dispersed frequency-modulated optical pulses are presented. A Miró model is used to set a peak-power limit for multi-FM pickets, taking into account nonlinear propagation in the optical components and conversion of frequency modulation into amplitude modulation because of diffraction.
  • The fiber front end built to support the demonstration of multi-FM beam smoothing on OMEGA EP is described. High-bandwidth pulse shaping, multi-FM phase modulation, spectral-amplitude compensation, chromatic dispersion compensation, and fail-safe systems have been implemented to provide seed pulses that meet all operational requirements.
  • A generalization of the extended Zakharov model of two-plasmon decay that includes the evolution of the electron-distribution function in the quasi-linear approximation is presented. This makes it possible to investigate anomalous absorption of laser light and hot-electron production caused by the two-plasmon–decay instability of multiple overlapping electromagnetic waves.
  • Particle-in-cell simulation results pertaining to cone-in-shell integrated fast-ignition experiments at the Omega Laser Facility, providing further evidence of the detrimental effects of pre-plasma in the cone is presented. Studies of hot-electron generation from laser/pre-plasma interactions and transport show that the generated hot electrons are dominated in number by low-energy electrons but in energy by multi-MeV electrons.
  • Experiments and models relating to dental calculus ablation in human teeth using 400-nm laser pulses are described. Calculus-removal rates, microscopy, and spectroscopy after irradiation are consistent with tissue-specific ablation at 400 nm caused by absorption by bacterial porphyrins within calculus. A heuristic model for calculus ablation agrees well with observed data.

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