Relativistic plasma nanophotonics for ultrahigh energy density physics

The heating of dense matter to extreme temperatures motivates the development of powerful lasers(1-4). However, the barrier the critical electron density imposes to light penetration into ionized materials results in the deposition of most of the laser energy into a thin surface layer at typically only 0.1% of solid density. Here, we demonstrate that trapping of femtosecond laser pulses of relativistic intensity deep within ordered nanowire arrays can volumetrically heat dense matter into a new ultrahot plasma regime. Electron densities nearly 100 times greater than the typical critical density and multi-keV temperatures are achieved using laser pulses of only 0.5 J energy. We obtained extraordinarily high degrees of ionization (for example, 52 times ionized Au) and gigabar pressures only exceeded in the central hot spot of highly compressed thermonuclear fusion plasmas. Scaling to higher laser intensities promises to create plasmas with temperatures and pressures approaching those in the centre of the Sun.