  We present a table-top beamline providing a soft X-ray supercontinuum
extending up to 350 eV from high-order harmonic generation with sub-13 fs 1300
nm driving pulses and simultaneous production of sub-5 fs pulses centered at
800 nm. Optimization of the high harmonic generation in a long and dense gas
medium yields a photon flux of ~2 x 10^7 photons/s/1% bandwidth at 300 eV. The
temporal resolution of X-ray transient absorption experiments with this
beamline is measured to be 11 fs for 800 nm excitation. This dual-wavelength
approach, combined with high flux and high spectral and temporal resolution
soft X-ray absorption spectroscopy, is a new route to the study of ultrafast
electronic dynamics in carbon-containing molecules and materials at the carbon
K-edge.
