Generation of high energy density by fs-laser-induced confined microexplosion

Confined microexplosion produced by a tightly focused fs-laser pulse inside transparent material proved to be an efficient and inexpensive method for achieving high energy density up to several MJ per cm(3) in the laboratory table-top experiments. First studies already confirmed the generation of TPa-range pressure, the formation of novel super-dense material phases and revealed an unexpected phenomenon of spatial separation of ions with different masses in hot non-equilibrium plasma of confined microexplosion. In this paper, we show that the intense focused pulse propagation accompanied by a gradual increase of ionization nonlinearity changes the profile and spectrum of the pulse. We demonstrate that the motion of the ionization front in the direction opposite to the pulse propagation reduces the absorbed energy density. The voids in our experiments with fused silica produced by the microexplosion-generated pressure above Young's modulus indicate, however, that laser fluence up to 50 times above the ionization threshold is effectively absorbed in the bulk of the material. The analysis shows that the ion separation is enhanced in the non-ideal plasma of microexplosion. These findings open new avenues for the studies of high-pressure material transformations and warm dense matter conditions by confined microexplosion produced by intense fs-laser.