Bright high-order harmonic generation from long gas jets toward coherent soft X-ray applications

We have performed the optimization of high-order harmonic brightness from long gas jets by using self-guided and chirped femtosecond laser pulses and analyzed their coherence properties. The characteristics of laser pulse propagation were analyzed both in theory and in experiments to understand the self-guiding process of laser pulses and chirp compensation mechanism. Highly efficient harmonic generation with low beam divergence and narrow bandwidth was achieved by applying these two techniques to the long gas jets. The coherence properties of the bright harmonics were examined using double-pinhole interference and spectral interference.