Laser-matter interaction in the bulk of a transparent solid: confined microexplosion and void formation

We present here the experimental and theoretical studies of a single femtosecond laser pulse interaction inside a bulk of transparent media (sapphire, glass, polymer). This interaction leads to the drastic transformations in a solid resulting in a void formation inside a dielectric. The laser pulse energy is absorbed within a volume of approximately $0.15\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}{\mathrm{m}}^{3}$ creating a pressure and temperature comparable to that in the core of a strong multi-kilo-tons explosion. The material within this volume is rapidly atomized, ionized, and converted into a tiny super-hot dense cloud of expanding plasma that generates strong shock and rarefaction waves which result in the formation of a void, whose diameter is $\ensuremath{\sim}200\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ (for a $100\phantom{\rule{0.3em}{0ex}}\mathrm{nJ}$ pulse in sapphire). The way this structure forms can be understood from high-temperature plasma hydrodynamics. We demonstrate that unique states of matter characterized by temperatures $\ensuremath{\sim}{10}^{5}\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, heating rates up to the ${10}^{18}\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{s}$, and pressures more than 100 times the strength of any material were created using a standard table-top laser in well-controlled laboratory conditions. We discuss the properties of the laser-affected solid and possible routes of laser-affected material transformation to the final state long after the pulse end. These studies will find application for the design of new materials and three-dimensional optical memory devices, and for formation of photonic band-gap crystals.