Production of plasma channels in gas-jets

Guiding focused pulses along path lengths much larger than the depth of focus is one of the major tasks for the progress of laser acceleration of electrons in plasmas. We will present the results of the production of hollow plasmas to be used as guiding medium, obtained inducing optical breakdown in Helium subsonic gas-jet with nanosecond laser pulses similar to the Amplified Spontaneous Emission (ASE) pedestal of a powerful ultrashort laser pulse. These plasmas have been then carefully characterized by the deconvolution, with original algorithms, of high quality interferograms obtained with high resolution interferometry and the relevant channel parameters were measured, including length, width, electron density at the channel axis and at its boundary. The electron density profiles we obtained match the requirements for an efficient guiding in laser wakefield acceleration (LWFA) experiments. The acceleration length can be further increased by using longer gas-jets and larger f/N numbers. New studies are planned with supersonic gas-jets, providing more homogeneous density profiles and steeper boundaries.

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