Compact ultra-intense lasers and nanostructures open a path to extreme pressures

Heating matter into the ultrahigh-energy density (UHED) regime characterized by pressures greater than a gigabar is a very challenging task. The UHED plasma regime is of interest for fusion studies; for the generation of intense flashes of x-rays, gamma rays, and high-energy particles, including neutrons; and for the study of atomic processes in the conditions encountered in extreme laboratory and astrophysical environments. Unfortunately, the creation of UHED plasmas in the laboratory has been mostly limited to the central hot-spot of these imploded capsules in the inertial confinement fusion experiments, and even some of today's most powerful lasers can fall short of achieving the UHED regime when irradiating solid flat targets. In this traditional plasma heating scheme, the leading edge of the intense laser pulse rapidly creates a plasma blow-off that prevents the remainder of the laser pulse from directly heating the solid density target. Heating by hot electrons using today's most energetic short-pulse lasers just surpassed the boundary into the UHED regime. Here, Rocca et al discuss a different approach to reach the UHED regime with compact, ultrashort-pulse lasers: the irradiation of high-aspect-ratio, vertically aligned nanowire arrays with ultrahigh-contrast femtosecond laser pulses of only joule-level energy focused to relativistic intensity.