The technology and application of coherent X-rays — attosecond science meets NLO

Light pulses from a femtosecond laser can be coherently upconverted to generate light in the extreme-ultraviolet and soft x-ray regions of the spectrum using high-order harmonic generation, a process where a large number of photons from an intense laser can be coherently combined. Advances in laser technology, combined with a better understanding of the high harmonic process, have made it possible to apply concepts from nonlinear optics to enhance and control the HHG process. A number of new scientific and technological applications have also been demonstrated that make use of the unique characteristics of HHG radiation: laser-like, full spatial coherence, ultrashort pulse duration, and high pulse repetition-rate.