Absorption-Limited Generation of Coherent Ultrashort Soft-X-Ray Pulses

Abstract

Coherent growth of high-order harmonic radiation has been extended to propagation lengths comparable to the XUV absorption length at wavelengths as short as 10 nm range for the first time. Absorption-limited production of high harmonics of sub-10-fs near-infrared laser pulses in gas jets gives rise to a harmonic conversion efficiency of $(3--4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ 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.