[en] We show the possibility of producing a short bunch of nearly bandwidth-limited few-cycle attosecond pulses based on time-dependent resonant interaction of an incident radiation pulse with the bound states of hydrogen-like atoms. Time-dependence of an atomic resonance is provided by a laser pulse far from resonance with an intensity well below the atomic ionization threshold via time-dependent tunnel ionization from the excited states and time-dependent adiabatic Stark splitting of the excited energy levels. Without external matching of the spectral components it is possible to produce pulses with durations up to 80 as at the carrier wavelength of 13.5 nm in Li²⁺-plasma, as well as pulses with durations up to 600 as at the carrier wavelength of 122 nm in atomic hydrogen. (paper)

[en] The role of quantum interference (QI) in spectra of the resonant Moessbauer scattering is investigated. As a mechanism ensuring the QI conditions, the radio-frequency (RF) mixing of the spin sublevels of the excited nuclear state is considered. It is shown that QI leads to a significant intensity redistribution of the elastic and Raman scattering.

[en] A model of Moessbauer absorption taking into account the effects of the electron relaxation and the nuclear levels anticrossing simultaneously has been proposed. The dependence of the absorption deficit (transparency) on the relaxation and mixing parameters has been obtained using the stochastic theory of Moessbauer relaxation spectra. The role of quantum interference in occurrence of a partial transparency on Moessbauer transitions has been explored under these conditions.

[en] The transformation of exponentially decaying waveform (the time dependence of detection probability) of a Mössbauer γ-ray photon into a regular sequence of short nearly bandwidth-limited pulses in a vibrating recoilless resonant absorber is studied. The case of dual-tone vibration at the fundamental frequency and its second harmonic under experimentally feasible conditions is considered. We show that this technique allows one to shorten pulses and increase the ratio of pulse separation to pulse length as well as to enlarge pulse amplitude compared to the pulses produced in harmonically vibrating absorber. The obtained results pave the way to the development of the time-resolved Mössbauer γ-ray spectroscopy and manipulation of quantum information in hard x-ray/γ-ray range. (paper)

[en] We experimentally study the influence of a radio-frequency magnetic field on the resonant absorption of gamma radiation in samples with high density of resonant nuclei. An increase of the integrated area of absorption spectra and a change in the relative intensity of hyperfine lines can be explained by the excitation of magnetostriction vibrations in the sample, resulting in reduction of the saturation effect of resonant absorption.