Dover, NNDoverCook, NNCookTresca, OOTrescaEttlinger, OOEttlingerMaharjan, CCMaharjanPolyanskiy, MMPolyanskiyShkolnikov, PPShkolnikovPogorelsky, IIPogorelskyNajmudin, ZZNajmudin2016-01-202016-02-092016-02-09Journal of Plasma Physics, 2016, 82 (1)1469-7807http://hdl.handle.net/10044/1/28948We report on the experimental demonstration of a technique to generate steep density gradients in gas jet targets of interest to laser plasma ion acceleration. By using an intentional low energy prepulse, we generated a hydrodynamic blast wave in the gas to shape the target prior to the arrival of an intense CO2 (λ ≈ 10 µm) drive pulse. This technique has been recently shown to facilitate the generation of ion beams by shockwave acceleration (Tresca et al. 2015). Here, we discuss and introduce a model to understand the generation of these blast waves and discuss in depth the experimental realisation of the technique, supported by hydrodynamics simulations. With appropriate prepulse energy and timing, this blast wave can generate steepened density gradients as short as l ≈ 20 µm (1/e), opening up new possibilities for laser-plasma studies with near-critical gaseous targets.© Cambridge University Press 2016 This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.Fluids & Plasmas0202 Atomic, Molecular, Nuclear, Particle And Plasma PhysicsJournal Articlehttps://www.dx.doi.org/10.1017/S002237781600012XEP/K022415/1ST/J002062/1 John Adams Inst