Monochromatic 2DKαEmission Images Revealing Short-Pulse Laser Isochoric Heating Mechanism

Abstract

The rapid heating of a thin titanium foil by a high intensity, sub-picosecond laser is studied by using a 2D narrow-band x-ray imaging and x-ray spectroscopy. A novel monochromatic imaging diagnostic tuned to 4.51 keV Ti Kα was used to successfully visualize a significantly ionized area (<Z> >17±1) of the solid density plasma to be within a ~ 35 μm diameter spot in the transverse direction and 2 μm in depth. The measurements and a 2D collisional Particle-in-cell simulation reveal that, in the fast isochoric heating of solid foil by intense laser light, such high ionization state in the solid titanium is achieved by thermal diffusion from the hot preplasma in a few picoseconds after the pulse ends. The shift of Kα and formation of a missing Kα cannot be explained with the present atomic physics model. The measured Kα image is reproduced only when a phenomenological model for the Kα shift with a threshold ionization of <Z>=17 is included. This work reveals how the ionization state and electron temperature of the isochorically-heated non-equilibrium plasma are independently increased.

Local wavelength evolution and Landau damping of electrostatic plasma wave driven by an ultra-relativistic electron beam in dense inhomogeneous plasma

“…Recently, experiments on energy transfer and dissipation in the interaction of intense laser or electron beams with plasma have been carried out [16][17][18][19][20][21][22]. Transport of highenergy electrons in plasmas is also relevant to many applications of intense lasers and particle accelerators, such as tabletop particle and radiation sources [23][24][25][26][27][28][29][30][31], as well as for diagnostics of materials under extreme conditions [32].…”

Isochoric heating of solid-density plasmas beyond keV temperature by fast thermal diffusion with relativistic picosecond laser light

“…The required timescale of the transition of the dominant heating mechanism from the REB to thermal diffusion is a few picoseconds [17]. In addition, thermal diffusion propagates from a hot preplasma on a picosecond timescale even after the laser pulse ends [18].…”

Fast collisional electron heating and relaxation in thin foils driven by a circularly polarized ultraintense short-pulse laser

“…Most laser-based isochoric heating experiments conducted so far have exploited the fast electrons driven by a linearly polarized laser pulse (Nilson et al 2010;Santos et al 2017;Sawada et al 2019). Their energy dissipation through the plasma bulk enables heating to high temperatures (0.1−1 keV) at solid-range plasma densities, but usually at the expense of poor spatial uniformity (Dervieux et al 2015) and relatively slow thermalization.…”