Micro Plasma Lens for Intensity Enhancement in Fast Ignition Applications

Miniature plasma lenses capable of withstanding high laser intensities could provide compact focusing elements for a variety of laser-plasma applications. In particular, they offer a simple route to increase ignitor beam intensity in fast ignition targets while remaining compatible with the geometric constraints of cone-in-target configurations. We report an experimental proof-of-concept demonstration of such a lens using a Ti:Sa femtosecond laser system. The lens is generated by a nanosecond laser pulse incident on a foil aperture, producing an expanding plasma with a transient radial density gradient that focuses a delayed femtosecond pulse. The resulting plasma lens focal spot is reduced to a few microns ⟨DFWHM⟩≈5.5μm. After accounting for transmitted energy contained within the FWHM contour, the effective intensity enhancement was estimated to be IPLI0≈47±15.