No abstract

A combined experimental-theoretical method of diagnostics of the plasma created on a surface of Ag target irradiated by intense femtosecond laser pulses is proposed. The method is based on semiempirical wide-range models of optical, transport and thermodynamic properties of Ag plasma. Numerical coefficients in these models are chosen so as to ensure the best accordance of simulations to measurements of a complex absorption coefficient of Ag plasma by means of femtosecond interference microscopy. A two-temperature hydrodynamic modelling of non-stationary laser-produced Ag plasma is carried out; calculated results are presented in comparison with experiments. Unexpectedly high values of the phase of the complex reflection coefficient at short (200 fs) time delay between pump and probe laser pulses are obtained experimentally; possible explanations of this phenomenon are discussed.

For the first time, the data have been obtained on the effects of high-intensity terahertz (THz) radiation (with the intensity of 30 GW/cm2, electric field strength of 3.5 MV/cm) on human skin fibroblasts. A quantitative estimation of the number of histone Н2АХ foci of phosphorylation was performed. The number of foci per cell was studied depending on the irradiation time, as well as on the THz pulse energy. The performed studies have shown that the appearance of the foci is not related to either the oxidative stress (the cells preserve their morphology, cytoskeleton structure, and the reactive oxygen species content does not exceed the control values), or the thermal effect of THz radiation. The prolonged irradiation of fibroblasts also did not result in a decrease of their proliferative index.

No abstract

Key words Two-temperature warm dense matter, action of ultrashort laser pulse, pump-probe technique.We combine theoretical and experimental methods to study the processes induced by fast laser heating of metal foils. These processes reveal themselves through motion of frontal (irradiated) and rear-side foil boundaries. The irradiated targets are 0.3-2 micron thick aluminum foils deposited on much thicker (150 microns) glass plate. The instant boundary positions is measured by pump-probe technique having ∼ 40 − 150 fs time and ∼ 1 nm spatial resolutions. Ultrashort laser pulse transforms a frontal surface layer with thickness dT into two-temperature (Te Ti) warm dense matter state. Its quantitative characteristics including its thickness are defined by poorly known coefficients of electron-ion energy exchange α and electron heat conductivity κ. Fast laser heating rises pressure in the dT -layer and therefore produce acoustic waves. Propagation and reflection from the frontal and rear boundaries of these waves causes the displacement Δx(t) of boundary positions. Pressure wave profiles, and hence functions Δx(t), depend on thickness dT . This is why the experimental detection of Δx(t) opens a way to accurate evaluation of the coefficients α and κ.

No abstract

No abstract

We demonstrate a simple approach to retrieve the original peak electric field (E-field) strength of high-intensity THz pulses using an electro-optic sampling (EOS) technique and the Poynting flux approach. The latter supposes assessment of THz pulse intensity by measurement of pulse energy, duration and spot size, but its applicability to a few-cycle THz pulse needs detailed consideration. We applied a deconvolution procedure to the raw EOS data to retrieve the THz field waveform. We describe a two-step procedure that allows us to assess the field strength of an extreme THz field. First, the EOS measurements of the THz field should be performed at low pulse energies to retrieve the THz waveform and estimate pulse duration and amplitudes of each particular oscillation. Next, the field strength of an extreme THz pulse can be assessed from the Poynting flux approach with correction to the abovementioned data obtained from the EOS measurements. We show good experimental coincidence between peak strength estimation from the EOS directly and from the combined approach at 'low' field strength. Hence, an extreme THz E-field strength can also be assessed from preliminary EOS measurements and full energy measurements based on the Poynting flux approach. We also show that the Poynting flux approach for extreme few-cycle THz pulses gives prominent, at least two-fold, underestimation without preliminary EOS measurements.