Generation of coherent hard-x-ray radiation in crystalline solids by high-intensity femtosecond laser pulses

A process for coherent hard-x-ray generation is suggested, which is based on the idea that high-intensity, ultrashort laser pulses can be coupled into a crystal before the lattice structure is destroyed. In the presence of the lattice periodicity, additional momentum can be transferred to the electrons that are moving in the strong light field. This additional momentum supplied by the crystal results in a substantial decrease of the threshold pump laser intensity required for hard-x-ray generation as compared to free electrons. The lattice is also utilized to select the frequency of the emitted x rays via Bragg coupling. A numerical estimation for the yield of the proposed mechanism gives an output power of some 10 W in the range of 1--10 keV of photon energies by using a state-of-the-art optical pulse with a peak intensity of about 10¹⁷ W/cm² and a pulse duration of 30 fs.