High-sensitivity optical tomography of instabilities in supersonic gas flow.

Characterization of gas targets relies largely on conventional optical techniques, providing millisecond time resolution, which not only overlooks the fluctuations occurring at shorter time scales but also often challenges the sensitivity limits of optical probing as their refractive index is close to unity. Hence, the ability to resolve these fluctuations needs to be addressed as it is paramount for accurate gas jet characterization for their applications, including laser-matter interaction in laser wakefield electron acceleration or plasma x ray sources. In this Letter, we introduce an advanced gas jet characterization system capable of visualizing fast density fluctuations by Schlieren imaging, combined with density characterization by interferometric tomography, both with increased sensitivity due to the four-pass probing configuration. We demonstrate that combining the two modalities provides a substantial advancement in achieving a comprehensive, both quantitative and qualitative, characterization of gas jets.

Generation of intense magnetic wakes by relativistic laser pulses in plasma.

The emergence of petawatt lasers focused to relativistic intensities enables all-optical laboratory generation of intense magnetic fields in plasmas, which are of great interest due to their ubiquity in astrophysical phenomena. In this work, we study generation of spatially extended and long-lived intense magnetic fields. We show that such magnetic fields, scaling up to the gigagauss range, can be generated by interaction of petawatt laser pulses with relativistically underdense plasma. With three-dimensional particle-in-cell simulations we investigate generation of magnetic fields with strengths up to [Formula: see text] G and perform a large multi-parametric study of magnetic field in dependence on dimensionless laser amplitude [Formula: see text] and normalized plasma density [Formula: see text]. The numerical results yield scaling laws that closely follow derived analytical result [Formula: see text], and further show a close match with previous experimental works. Furthermore, we show in three-dimensional geometry that the decay of the magnetic wake is governed by current filament bending instability, which develops similarly to von Kármán vortex street in its nonlinear stage.