Plasma may facilitate combining 61 laser beams into a single, collimated beam

Extreme optical fluences far exceeding the laser damage threshold of traditional optics play an important role in high-energy-density physics, which studies matter subjected to very high pressures. One potential mechanism for producing a fluence, or radiant energy flux, of this caliber is cross-beam energy transfer (CBET), which allows energy from multiple beams to be transferred to a single beam in a hot, underdense plasma.

A new article in Physics of Plasmas describes the effort to design and test such a plasma beam combiner for the National Ignition Facility (NIF), a large laser-based inertial confinement fusion research device at Lawrence Livermore National Laboratory.

The phenomenon of stimulated Brillouin scattering can lead to amplification of a beam’s power and energy through interactions with additional crossing beams in a plasma. In the current study, the authors determined through modeling and simulation that energy from 61 different laser beams incident at various angles could be resonantly combined into a single, collimated beam.

Initial experiments to test the beam combiner used up to eight pumping beams to produce resonant amplification of a single-seed beam. The output energy reached 4.2 kilojoules in one nanosecond, which is more than triple the energy in any of the incident beams in that time period. It is also greater than what is otherwise available at NIF in terms of beams with one-nanosecond pulses at this particular wavelength.

The experimental results agree well with previous CBET models and are a promising first step to the eventual goal of combining all 61 laser beams. The authors hope that this line of work may produce optical devices made from plasmas that can withstand extreme fluences and intensities.

Source: “A plasma amplifier to combine multiple beams at NIF,” by R. K. Kirkwood, D. P. Turnbull, T. Chapman, S. C. Wilks, M. D. Rosen, R. A. London, L. A. Pickworth, A. Colaitis, W. H. Dunlop, P. Poole, J. D. Moody, D. J. Strozzi, P. A. Michel, L. Divol, O. L. Landen, B. J. MacGowan, B. M. Van Wonterghem, K. B. Fournier, and B. E. Blue, Physics of Plasmas (2018). The article can be accessed at https://doi.org/10.1063/1.5016310 .