Laser matter interaction in the bulk of transparent dielectrics: Confined micro-explosion

Abstract

We present here the experimental and theoretical studies of drastic transformations induced by a single powerful femtosecond laser pulse tightly focused inside a transparent dielectric, that lead to void formation in the bulk. We show that the laser pulse energy absorbed within a volume of less than 1μm3 creates the conditions with pressure and temperature range comparable to that formed by an exploding nuclear bomb. At the laser intensity above 6 × 1012 W/cm2 the material within this volume is rapidly atomized, ionized, and converted into a tiny super-hot cloud of expanding plasma. The expanding plasma generates strong shock and rarefaction waves which result in the formation of a void. Our modelling indicates that unique states of matter can be created using a standard table-top laser in well-controlled laboratory conditions. This state of matter has temperatures 105 K, heating rate up to the 1018 K/s, and pressure more than 100 times the strength of any solid. The laser-affected sites in the bulk were detected ("read") by generation of white continuum using probe femtosecond pulses at much lower laser intensity of 1010 W/cm 2 - 1011 W/cm2. Post-examination of voids with an electron microscope revealed a typical size of the void ranges from 200 to 500 nm. These studies will find application for the design of 3D optical memory devices and for formation of photonic band-gap crystals.