Synthesis of super-dense phase of aluminum under extreme pressure and temperature conditions created by femtosecond laser pulses in sapphire

Abstract

We describe synthesis of a new super-dense phase of aluminum under extreme pressure and temperature conditions created by laser-induced microexplosions in sapphire. Micro explosions in sub-micrometer sized regions of sapphire were induced by tightly-focused femtosecond laser pulses with a temporal length of ~ 100 fs and an energy of ~ 100 nJ. Fast, explosive expansion of photogenerated high-density plasma created strong heating and pressure transients with peak temperature and pressure of ~ 105 K and 10 TPa, respectively. Partial decomposition of sapphire in the shock-compressed sapphire led to formation of nanocrystalline bcc-Al phase, which is different from ambient fcc-Al phase, and was permanently preserved by fast quenching. The existence of super-dense bcc-Al phase was confirmed using X-ray diffraction technique. This is the first observation of bcc-Al phase, which so far has been only predicted theoretically, and a demonstration that laser-induced micro explosions technique enables simple, safe and cost-efficient access to extreme pressures and temperatures without the tediousness typical to traditional techniques that use diamond anvil cells, gas guns, explosives, or megajoule-class lasers.