  It has been proven that the intense tightly focused Gauss beam (GB) generates
pressures in excess of a few TPa creating the novel super-dense phases of
Aluminium and silicon [1-5]. Recently it was demonstrated that the Bessel beam
(BB) focused inside sapphire produced the cylindrical void being two orders of
magnitude larger than that generated by the GB [6-8]. Analysis of the
experimental data presented below allows making the remarkable conclusions
based solely on the void size measurements without any ad hoc assumptions about
the interaction process. First, the void size is direct evidence of strong
(>40%) absorption of the pulse energy. Second, it is a direct experimental
evidence of the high-energy concentration in the central spike of the focus.
The unique features of the intense Bessel beam interaction then allow
understanding the experimental observation. This interaction generates early in
the pulse time the spatial distribution of excited permittivity changing from
positive to negative values. Then the light interacts with
zero-real-permittivity surface, separating plasma and dielectric areas, which
leads to high energy concentration near the axis of cylindrical focus up to
several MJ/cm3 (pressure range of 4-8 TPa). The effect depends on the angle
between the permittivity gradient and the field polarisation. High pressure
generates intense cylindrical shock/ rarefaction waves, which led to formation
of void and compressed shell. We demonstrate that the Bessel beam proves to be
an effective tool for producing extreme pressure/temperature conditions on the
laboratory tabletop. It appears that adjusting polarisation and permittivity
gradient might be a novel way for increasing the maximum pressure. This tool
allows for search of novel high-pressure material phases, for the 3D laser
machining and for creating Warm Dense Matter as those in star cores.
