[en] The effects of the interaction of an intense femtosecond laser pulse with large atomic clusters are considered. The pulse intensity is of the order of 10¹⁸ W cm^-2. New effects appear when the magnetic component of the Lorentz force is taken into account. The second harmonic of laser radiation is generated. The second harmonic generation (SHG) efficiency is proportional to the square of the number of atoms in a cluster and the square of the laser radiation intensity. The resonance increase in the SHG efficiency at the Mie frequencies (both at the second-harmonic frequency and fundamental frequency) proved to be insignificant because of a fast passage through the resonance during the cluster expansion. The mechanisms of the expansion and accumulation of energy by electrons and ions in the cluster are discussed in detail. The energy accumulation by electrons mainly occurs due to stimulated inverse bremsstrahlung upon elastic reflection of the electrons from the cluster surface. The equations describing the cluster expansion take into account both the hydrodynamic pressure of heated electrons and the Coulomb explosion of the ionised cluster caused by outer shell ionisation. It is assumed that both inner shell and outer shell ionisation is described by the over-barrier mechanism. It is shown that atomic clusters are more attractive for generation of even harmonics than compared to solid and gas targets. (superstrong laser fields)

[en] The phase sensitivity of the atomic ionization by intense one-cycle linearly polarized laser pulses is discussed within the analytic Landau-Dykhne approximation. The generalized Keldysh parameter is introduced for analysis of two regimes of ionization. In the case of super-intense laser field we found that ionization by cosine waveform pulse is much more effective than that by sine waveform pulse with the same energy in the pulse. This is a pure quantum destructive interference effect. Electron energy spectra and effective electron temperatures are also derived analytically for both waveform pulses

[en] We investigate one of the possibilities for production of carriers in diamond resulting in its absolute negative conductivity at low temperatures T ∼ 10 – 30 K. Production and dynamics of electrons and holes in diamond at the irradiation by picosecond laser pulse with the peak laser intensity of 10¹⁰ W/cm² has been considered and compared to each other. Then carriers are cooled due to emission of acoustic phonons. Diamond heating is estimated in focussing region. The conclusion has been made about small local increasing of lattice temperature in the irradiation region. Thus, laser irradiation can produce conditions for possible experimental observation of an absolute negative conductivity of diamond at low temperatures

[en] We consider the negative conductivity of electrons in semiconductors excited by a picosecond laser pulse at low temperatures, due to the inelastic electron-phonon collisions. For the first time, the dependence of the deformation potential on the phonon wave number is taken into account. This dependence significantly changes the region of negative electron conductivity as a function of the phonon temperature