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We present the results of experimental studies of formation and evolution of multiply ionized (multicharged) laser
micro-size plasma produced in gases (air, nitrogen, argon and helium) and inside the transparent solids (fused silica) with
high intensity (up to ~ 1017 W/cm2), ultrashort (τ ~100 fs), 800nm/400nm laser pulses tightly focused in a region of ~1.5
μm in diameter. The measuring techniques and experimental setups for generation and precise optical diagnostics of
laser-induced plasma - pump-probe microinterferometry and ultrafast spectroscopy are described. The measured
spatiotemporal distributions of plasma refractive index/electron density and plasma spectra are demonstrated. In the
experiments, the main attention was paid to the most intriguing initial stage of ultrafast plasma formation and evolution
characterized by strong laser-matter and laser-plasma coupling resulting in efficient photoionization of material and
plasma heating. We found out that the almost complete ionization (down to nuclei) of the initial gas occurs even at the
initial stage of plasma formation. Besides, it was observed, for the first time, that a characteristic time of laser plasma
formation considerably (in times) exceeds the duration of the pump laser pulse. This postionization process is attributed
to impact ionization of plasma by hot electrons heated due to inverse bremsstrahlung. A theoretical model describing the
mechanism of plasma postionization by hot photoelectrons was proposed. We compare the results of the experiments
with what the theory predicts - the results of electron density calculations are in good agreement with the experimental
data. The dynamics of plasma emission (spectral continuum and spectral line formation) in UV-visible spectral range
was investigated with a picosecond time resolution applying the developed ultrafast streak-camera-based spectrometer.
The spatiotemporal distributions of refractive index of laser irradiated fused silica were recorded with pump-probe
microinterferometry. It was demonstrated that the induced refractive index of laser-matter interaction area changes its
sign from the positive to the negative during the laser irradiation and again to the positive one after the laser pulse ends.
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