Bright extreme-ultraviolet high-order-harmonic radiation from optimized pulse compression in short hollow waveguides

Multimodal nonlinear propagation dominates the evolution of intense laser pulses propagating in high-pressure gas-filled capillaries used for high harmonic generation. A fully multimodal nonlinear propagation model is used to predict pulse evolution along such a capillary, and the length and pressure distribution are optimized to produce the shortest pulses at the capillary output. This optimization is shown theoretically to result in self-compression of the pulse from ~53 to ~7 fs, and is shown experimentally to increase the flux of high harmonic radiation from the capillary by an order of magnitude over comparable capillary and gas jet designs.