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.

Plasma plumes produced by laser ablation of Al with single and double pulse schemes.

We generated and characterized plasma with single and double picosecond laser pulses to study the plume dynamics and to control the plasma properties. The double pulse scheme was found to be superior for generating a homogeneous plasma. Lateral expansion was prominent in irradiation schemes wherein the energy in the first pulse is lower than or equal to that of the second pulse. The velocities of the fast and slow species were found to be nearly equal with the emission counts corresponding to slow species being larger for the single pulse compared to the double pulse.