Raman Scattering and Chirped Pulse Amplification in Plasma

A high efficiency broad-band Raman chirped pulse amplifier is being developed. The scheme involves a short seed pulse injected into a preformed plasma waveguide channel where it is amplified by a counter-propagating, high energy, long duration chirped pump pulse. Energy is transferred from the pump to the seed by resonant excitation of a plasma wave (see this publication in Phys. Rev. Lett.)

This new type of amplifier presents unique features:
• Plasma, being a broken down medium, can sustain much higher power densities than other amplifying media. Moreover interactions can take place over several cm.
• A chirped pump distributes the gain spatially and provides the bandwidth necessary to either amplify a short pulse or compress a long pulse.
• For a chirped pump pulse or a sufficiently intense seed pulse, the superradiant regime can be accessed which allows for strong amplification and compression of the seed pulse.

Moreover not only the Raman amplification mechanism represents a extremely interesting new scheme to amplify short laser pulses without the need of using a stretcher and a compressor, but it can also have important implications for particle acceleration since it could provide a means of energy replenishment for the main short laser pulse. It could therefore play in a role in the staging of multiple accelerating structures.

Snapshots of amplitudes of probe vector potential g (top), developing from a short seed, and corresponding density modulations h (bottom) where g0 is the small-signal growth rate and hlim is the limiting value of h.




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University of Strathclyde, Glasgow, U. K.