Absorption-limited generation of coherent ultrashort soft-X-ray pulses

Coherent growth of high-order harmonic radiation has been extended to propa gation lengths comparable to the XUV absorption length at wavelengths as sh ort as 10 nm range for the first time. Absorption-limited production of hig h harmonics of sub-10-fs near-infrared laser pulses in gas jets gives rise to a harmonic conversion efficiency of (3-4) x 10(-8) in the range of 10-13 nm in neon and some 2 orders of magnitude higher at about 30 nm in argon. This kHz-repetition-rate ultrafast soft-x-ray source emits approximately 10 (10) photons per sec within a 0.9-nm bandwidth of a typical Mo:Si mirror at 13.4 nm in a near-diffraction-limited beam and opens up the way to soft-x- ray nonlinear optics and the measurement of-sub-fs soft-x-ray pulses.