Chirped pulse Raman amplification in warm plasma: towards controlling saturation.
Stimulated Raman backscattering in plasma is potentially an efficient method of amplifying laser pulses to reach exawatt powers because plasma is fully broken down and withstands extremely high electric fields. Plasma also has unique nonlinear optical properties that allow simultaneous compression of optical pulses to ultra-short durations. However, current measured efficiencies are limited to several percent. Here we investigate Raman amplification of short duration seed pulses with different chirp rates using a chirped pump pulse in a preformed plasma waveguide. We identify electron trapping and wavebreaking as the main saturation mechanisms, which lead to spectral broadening and gain saturation when the seed reaches several millijoules for durations of 10's - 100's fs for 250 ps, 800 nm chirped pump pulses. We show that this prevents access to the nonlinear regime and limits the efficiency, and interpret the experimental results using slowly-varying-amplitude, current-averaged particle-in-cell simulations. We also propose methods for achieving higher efficiencies.
University of Strathclyde, SUPA, Department of Physics, Glasgow G4 0NG, United Kingdom.
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Yang
University of Strathclyde, SUPA, Department of Physics, Glasgow G4 0NG, United Kingdom.
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Vieux
University of Strathclyde, SUPA, Department of Physics, Glasgow G4 0NG, United Kingdom.
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Brunetti
University of Strathclyde, SUPA, Department of Physics, Glasgow G4 0NG, United Kingdom.
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Ersfeld
University of Strathclyde, SUPA, Department of Physics, Glasgow G4 0NG, United Kingdom.
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Farmer
UNIST, Banyeon-ri 100. Ulju-gun, Ulsan 689-798, South Korea.
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Hur
University of Strathclyde, SUPA, Department of Physics, Glasgow G4 0NG, United Kingdom.
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Issac
University of Strathclyde, SUPA, Department of Physics, Glasgow G4 0NG, United Kingdom.
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Raj
University of Strathclyde, SUPA, Department of Physics, Glasgow G4 0NG, United Kingdom.
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Wiggins
University of Strathclyde, SUPA, Department of Physics, Glasgow G4 0NG, United Kingdom.
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Welsh
University of Strathclyde, SUPA, Department of Physics, Glasgow G4 0NG, United Kingdom.
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Yoffe
University of Strathclyde, SUPA, Department of Physics, Glasgow G4 0NG, United Kingdom.
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Jaroszynski