Dynamics of plasma production and development in gases and transparent solids irradiated by high-intensity, tightly focused picosecond laser pulses

The results of experimental studies of the dynamics of formation and development of a laser plasma produced in microvolumes of gases (air) and transparent solids (fused silica) by high-intensity [$I\simeq(1-2)\times10^{14}$ W см$^{-2}$], $\sim22$-ps, 539-nm laser pulses tightly focused in a region of diameter 4 $\mu$m are presented. The spatiotemporal distributions of the refractive index and the electron density are studied by the interferometric method with a spatial resolution of $\sim1.6$ $\mu$m and a temporal resolution of $\sim3$ ps directly during the action of excitation picosecond laser pulses. An almost complete ionisation of the initial gas was shown to occur even in the initial stage of air plasma formation, within a few picoseconds after plasma production. The irradiation of solid transparent dielectrics (fused silica) by picosecond laser pulses resulted in a reversible production of a plasma with an electron density above 10$^{20}$ cm $^{-3}$, which did not cause the damage of dielectrics.