Quest for MeV frequency combs -- proposal for ELI experiments
  The optical frequency comb has become an indispensable tool for high precision spectroscopy. Also experiments in the field of ultrafast physics rely on the frequency comb technique to generate precisely controlled attosecond optical pulses by means of the high-order harmonic generation. However, in order to generate even shorter laser pulses or to apply this technique in investigations of nuclear structure, combs of frequencies of the order of MeV are necessary. It seems that it may not be possible to achieve such photon energies by high-order harmonic generation. In this context the possibility of the generation of Thomson and Compton-based frequency combs is presented. Diffraction of generated radiation by a sequence of laser pulses and its analogy to the diffraction grating is elucidated. Theoretical investigations presented in this report can be considered as the proposal for future ELI experiments [www.eli-laser.eu] 
Katarzyna Krajewska and Jerzy Z. Kami\'nski
physics.optics quant-ph