Atomic and molecular coherence produced by strong optical ultra-short pulses: generation of X-ray and gamma-ray radiation

Yuri V. Rostovtsev

Department of Physics, University of North Texas
Denton, Texas~76203

Recent progress in ultrashort, e.g. attosecond, laser technology allows researchers nowdays to obtain ultra-strong fields which
can be the same order of magnitude as the electric field created by an atomic nucleus. Interaction of such strong and broadband
field with atomic systems even under the action of a far-off resonance strong pulse of laser radiation should be revisited and as
we have shown that such pulses can excite remarkable coherence on high frequency transitions. We have found and analyzed
analitical solutions for various pulse shapes. We discuss the CEP effects and possible applications of obtained results to cooperative
generation of XUV and nuclear radiation. We compare our approach to short-wavelength high-harmonic generation.
For a sample with density of atoms or ions of the order of $10^{16}-10^{19}$ cm$^{-3}$, the density of excited nucleus
can be as much as $102-105$ cm$^{-3}$, and all nuclei, that are coherently oscillating in phase produce a cooperative burst
of gamma-ray radiation 10-1000 time shorter than the relaxation time, 100 ns for $^{57}$Fe.