Phase-matched generation of highly coherent radiation in water window region.

Highly coherent extreme ultraviolet radiation around the water window region (~4.4 nm) is generated in a semi-infinitive helium gas cell using infrared pulses of wavelength 1300 nm, energy 2.5 mJ, duration 40 fs, and repetition rate 1 kHz. The pressure-squared dependence of the intensity and the almost-perfect Gaussian profile and low divergence of the high harmonic source indicate a phase-matched generation process. The spatial coherence of the source is studied using Young's double-slit measurements.

High-harmonic-generation spectrum reconstruction from Young's double-slits interference pattern using the maximum entropy method.

A method is proposed that uses maximum entropy analysis of a Young's two-slit interference pattern for the measurement of the spectrum of a high-harmonic-generation light source. The approach is tested using experimental data, and the results are found to be consistent with those obtained directly using a grazing incidence spectrometer.