Ultrafast coherent and incoherent X-ray generation by inner-shell atomic processes induced by < 25 fs, > 1 J pulses of high power CPA lasers

Abstract

A new class of keV X-ray lasers based on specific inner-shell atomic transitions is analyzed. It is shown that population inversion between inner-shell vacancy levels of medium-Z elements can be created using only electron collisional ionization, or by using fast, incoherent X-ray pumping if the decay of the lower states is mediated by Coster-Kronig or super-Coster-Kronig processes. The requirements of extremely fast energy deposition on a target in order to compete with the inherently fast (0.1-20 fs) atomic processes can be fulfilled by use of an ultrahigh peak power laser system with ultrashort pulse duration. A state-of-the-art chirped pulse amplification (CPA) laser system delivering more than 1 J of optical energy in less than 25 fs with 10 Hz repetition rate is described. The laser system has also been used to produce high-brightness, narrow-linewidth incoherent X-rays that are optimal for time dependent X-ray diffraction studies. The design of sandwiched multilayer target structure and possible experimental configurations for effective production of coherent X-ray radiation are suggested. Preliminary experimental results of ultrafast (similar to 25 fs), high intensity (>10(19) W/cm(2)) excitation of layered metal targets show anomalous enhancement of specific Ti lines in the 2-14 nm wavelength range.