Abstract
The complex physics of the interaction between short-pulse ultrahigh-intensity lasers and solids is so far difficult to access experimentally, and the development of compact laser-based next-generation secondary radiation sources, e.g., for tumor therapy, laboratory astrophysics, and fusion, is hindered by the lack of diagnostic capabilities to probe the complex electron dynamics and competing instabilities. At present, the fundamental plasma dynamics that occur at the nanometer and femtosecond scales during the laser-solid interaction can only be elucidated by simulations. Here we show experimentally that small-angle x-ray scattering of femtosecond x-ray free-electron laser pulses facilitates new capabilities for direct in situ characterization of intense short-pulse laser-plasma interactions at solid density that allows simultaneous nanometer spatial and femtosecond temporal resolution, directly verifying numerical simulations of the electron density dynamics during the short-pulse high-intensity laser irradiation of a solid density target. For laser-driven grating targets, we measure the solid density plasma expansion and observe the generation of a transient grating structure in front of the preinscribed grating, due to plasma expansion. The density maxima are interleaved, forming a double frequency grating in x-ray free-electron laser projection for a short time, which is a hitherto unknown effect. We expect that our results will pave the way for novel time-resolved studies, guiding the development of future laser-driven particle and photon sources from solid targets.
- Received 2 January 2018
- Revised 7 June 2018
DOI:https://doi.org/10.1103/PhysRevX.8.031068
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Extreme states of matter generated by irradiation of a solid with ultrashort high-power laser pulses are used in applications such as laboratory astrophysics, novel particle accelerator concepts, and laser fusion. The lasers generate hot, dense plasmas that are a source for relativistic and strong electron currents and hence for nonlinear dynamics happening within only a few femtoseconds on nanometer scales. However, this behavior can be measured only indirectly or with insufficient spatial or temporal resolution. Here, we present the first measurement of plasma expansion, driven by a near-relativistic high-intensity short-pulse laser, to the nanometer and few femtosecond level, and we demonstrate the usefulness of this method for measuring important dynamics previously accessible only with simulations.
We target a high-intensity laser at a silicon grating and then use small-angle x-ray scattering of an x-ray free-electron laser to monitor changes in the grating surface. Expanding plasmas lose short-range correlations, which we measure down to the nanometer level by fitting the signal at large scattering angles. This allows us to observe the generation and expansion of the plasma at unexplored scales, revealing a transient grating structure in the plasma itself.
This study opens the window for new observations on unprecedented spatial and temporal scales, such as the development of plasma instabilities, nonlinear electron motion at the surface of a material, or rapid target heating in future studies of intense short-pulse laser experiments on solid targets.
