In this paper we investigate the single and double ionization signals of H2 molecules, with fixed and moving nuclei, as a function of laser intensity, for two different values of laser wavelength =390 nm and =780 nm, using an approach for evaluating the ionization signals which allows the investigation of rela- tively long-lasting pulses. The He system is first investigated to benchmark our calculation against already known results. We confirm the evidence of nonsequentiality in the ionization processes of all the systems investigated. Furthermore, we show that the nuclei motion enhances the double ionization signals by means of a mechanism which is very similar to a charge-resonant enhanced ionization CREI effect Zuo and Bandrauk, Phys. Rev. A 52, R2511 1995

The wave function of a two-level atom driven by a low-frequency laser pulse is obtained in analytical form and is used to determine the power spectrum of the dipole moment of the atom for different initial atomic states. The solution goes over some known approximate solutions and gives the energy of the two dressed states, the position of the hyper-Raman lines, the amplitudes both of the hyper-Raman lines and of the odd harmonics, and the position of the cutoff. The form of the hyper-Raman spectrum results independently of the initial atomic state and shows an onset and a cutoff of the emission.

We present the results of experimental and theoretical studies of high-order harmonic generation (HHG) in plasmas containing fullerenes using pulses of different duration and wavelength. We find that the harmonic cutoff is extended in the case of few-cycle pulses (3.5 fs, 29th harmonic) compared to longer laser pulses (40 fs, 25th harmonic) at the same intensity. Our studies also include HHG in fullerenes using 1300 and 780 nm multicycle (35 and 40 fs) pulses. For 1300 nm pulses, an extension of the harmonic cutoff to the 41st order was obtained, with a decrease in conversion efficiency that is consistent with theoretical predictions based on wave packet spreading for single atoms. Theoretical calculations of fullerene harmonic spectra using the single active electron approximation were carried out for both few-cycle and multicycle pulses.

The spectrum emitted by a three-level atom in the presence of a weak laser field is given together with the population dynamics and the phase of the Fourier transform of the acceleration. Calculations show that the spectrum can be very different from that emitted by a two-level atom. When the trapping conditions are obtained, the coupling to the third level can result in a large change in the spectrum

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The tunneling ionization of exotic atoms such as muonic hydrogen, muonium and positronium in a strong laser field of circular polarization is investigated taking into account the impact of the motion of the center of mass on the the tunneling ionization dynamics. The momentum partition between the ionization products is deduced. The effect of the center of mass motion for the momentum distribution of the ionization components is determined. The effect scales with the ratio of the electron (muon) to the atomic core masses and is nonnegligible for exotic atoms, while being insignificant for common atoms. It is shown that the electron (muon) momentum shift during the under-the-barrier motion due to the magnetically induced Lorentz force has a significant impact on the momentum distribution of the atomic core and depends on the ratio of the electron to the atomic core masses

The time-dependent wave function of a nanoring driven by a laser field is obtained by exploiting the symmetries\ud inherent to the system and used for studying the properties of the electromagnetic radiation emitted by the\ud nanoring as a function of the polarization state of the laser. The diffused radiation has the characteristics of\ud high-order-harmonic generation. For a noncircularly polarized laser field an extension of the expected cutoff\ud position is evident, indicating that nanorings are efficient sources of radiation. The polarization state of the\ud emitted harmonics can be opportunely controlled by varying the parameters of the pump field. The profile of\ud the absorbed angular moment shows that a magnetic moment can be induced depending on the polarization of\ud the driven field

The spectrum of radiation emitted by an electron colliding with a nucleus in the presence of a monochromatic laser field is calculated. The Coulomb potential is treated at all orders and the radiation is seen as spontaneous transition between two free states. The kinetic energy of the electron is T 9 100--3000 eV and the laser intensity I 9 101~ W/cm2; in this condition we see strong enhancement in the bremsstrahlung cross-section when the emitted frequency is an integral multiple of the laser frequency.PACS 32.80 -Photon interactions with atoms. PACS 41.70 -Particles in electromagnetic fields (including synchrotron radiation).