V. A. Antonov

Conversion of recoillessγradiation into a periodic sequence of short intense pulses in a set of several sequentially placed resonant absorbers

An efficient technique to produce a periodic sequence of ultrashort pulses of recoilless gamma-radiation via its transmission through the optically thick vibrating resonant absorber was demonstrated recently [Nature, 508, 80 (2014)]. In this work we extend the theoretical analysis to the case of a set of multiple absorbers. We consider an analytical model describing the control of spectral content of a frequency modulated gamma-radiation by selective correction of amplitudes and initial phases of some spectral components, using, respectively, the resonant absorption or dispersion of nuclei. On the basis of the analytical solutions we determine the ultimate possibilities of the proposed technique.

Coherent forward scattering of γ-ray and XUV radiation in the medium with the modulated quasi-resonant transition

We establish a close physical analogy between coherent forward scattering of γ-ray radiation in the vibrating quasi-resonant nuclear absorber and the XUV field propagation in the quasi-resonant atomic medium in the presence of the moderately strong IR field. We prove that both processes, under certain conditions, are described by similar Maxwell–Bloch equations for a two-level medium with modulated parameters of the resonant transition. It results in similar transformation of both γ-ray and XUV fields at the exit from the medium, fully determined by the characteristics of applied modulation and spectral content of the incident fields. We find an appropriate analytical solution describing transformation of the electromagnetic field as a result of its propagation in the modulated medium. We show, in particular, that recently observed effects of (i) suppressed resonant absorption in coherent γ-ray scattering of vibrating absorber and (ii) ionization rate modulation in IR pump–XUV probe experiments, present themselves as different manifestations of the same general physical phenomenon of modulation induced transparency (MIT). That transparency is induced by modulating the parameters of the resonant transition. While only partial MIT was observed so far, we suggest certain conditions for conducting some realistic experiments, which should demonstrate nearly 100% transparency in both processes.