The properties of supersonic, compressible plasma turbulence determine the behavior of many terrestrial and astrophysical systems. In the interstellar medium and molecular clouds, compressible turbulence plays a vital role in star formation and the evolution of our galaxy. Observations of the density and velocity power spectra in the Orion B and Perseus molecular clouds show large deviations from those predicted for incompressible turbulence. Hydrodynamic simulations attribute this to the high Mach number in the interstellar medium (ISM), although the exact details of this dependence are not well understood. Here we investigate experimentally the statistical behavior of boundary-free supersonic turbulence created by the collision of two laser-driven high-velocity turbulent plasma jets. The Mach number dependence of the slopes of the density and velocity power spectra agree with astrophysical observations, and supports the notion that the turbulence transitions from being Kolmogorov-like at low Mach number to being more Burgers-like at higher Mach numbers.

Ion acceleration in electrostatic collisionless shocks is driven by the interaction of the high-power laser with specially tailored near-relativistic critical density plasma. 2D EPOCH particle-in-cell simulations show that the ion acceleration is dependent on the target material used. In materials with low charge-tomass ratio hZ=Ai, proton beams with high flux and low energy spread are generated. In multi-ion plasmas the ions with different hZ=Ai acquire different velocities under a non-oscillating component of electrostatic field in the upstream region. This relative drift between the protons (hZ=Ai ¼ 1) and the lower hZ=Ai ions leads to the excitation of electrostatic ion two-stream instability. This in turn generates a low-velocity component in the upstream expanding protons. The velocity distribution of the upstream expanding protons is further broadened toward the higher velocity by the electrostatic ion two-stream instability between reflected protons, which results in large number of protons being accelerated by the shock.

The production of intense x-ray and particle sources is one of the most remarkable aspects of high energy laser interaction with a solid target. Wide application of these laser-driven secondary sources requires a high yield, which is partially limited by the amount of laser energy absorbed by the target. Here, we report on the enhancement of laser absorption and x-ray and particle flux by target surface modifications. In comparison to targets with flat front surfaces, our experiments show exceptional laser-to-target performance for our novel cone-shaped silicon microstructures. The structures are manufactured via laser-induced surface structuring. Spectral and spatial studies of reflectance and x-ray generation reveal significant increases of the silicon K a line and a boost of the overall x-ray intensity, while the amount of reflected light decreases. Also, the proton and electron yields are enhanced, but both temperatures remain comparable to those of flat foil targets. We support the experimental findings with 2D particle in cell simulations to identify the mechanisms responsible for the strong enhancement. Our results demonstrate how custom surface structures can be used to engineer high power laser-plasma sources for future applications.

X-ray absorption spectroscopy is a well-accepted diagnostic for experimental studies of warm dense matter. It requires a short-lived X-ray source of sufficiently high emissivity and without characteristic lines in the spectral range of interest. In the present work, we discuss how to choose an optimum material and thickness to get a bright source in the wavelength range 2 Å–6 Å (∼2 keV to 6 keV) by considering relatively low-Z elements. We demonstrate that the highest emissivity of solid aluminum and silicon foil targets irradiated with a 1-ps high-contrast sub-kJ laser pulse is achieved when the target thickness is close to 10 µm. An outer plastic layer can increase the emissivity even further.

Graphene is known as an atomically thin, transparent, highly electrically and thermally conductive, light-weight, and the strongest 2D material. We investigate disruptive application of graphene as a target of laser-driven ion acceleration. We develop large-area suspended graphene (LSG) and by transferring graphene layer by layer we control the thickness with precision down to a single atomic layer. Direct irradiations of the LSG targets generate MeV protons and carbons from sub-relativistic to relativistic laser intensities from low contrast to high contrast conditions without plasma mirror, evidently showing the durability of graphene.