Abstract
We present a table-top beamline providing a soft X-ray supercontinuum extending up to 370 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 high harmonic generation in a long and dense gas medium yields a photon flux of ~ 1.4 × 106 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.
Highlights
Transient absorption spectroscopy with high-order harmonic generation (HHG) sources is established as a powerful technique to probe ultrafast dynamics in atoms[1,2,3], molecules[4,5,6] and solids[7,8,9,10]
While the first soft X-ray (SXR) photons produced with a HHG source utilized high intensity 800 nm driving wavelength in a strong ionization regime[14,15], the strategy that is preferred is to use longer wavelength drivers in the short-wave infrared (SWIR)[12,16,17,18] and mid-infrared[19]
More conventional approaches relying on the post-compression of 30–50 fs idler pulses from Ti:sapphire-pumped Optical Parametric Amplifiers (OPA) produced SXR radiation supporting isolated
Summary
The simultaneous production of millijoule-level sub-13 fs pulses at 1300 nm and sub-5 fs pulses at 800 nm with two parallel hollow-core fiber compressors has been demonstrated. The few-cycle SWIR pulses can produce a high-flux high-harmonic supercontinuum in the soft X-ray region, with ~4.5 × 107 photons/s in 1% bandwidth at 200 eV and ~1.4 × 106 photons/s in 1% bandwidth at 300 eV. This brightness allows measurement of absorption spectra in the gas phase in a few seconds, an order of magnitude improvement compared to existing SXR HHG. A temporal resolution of ~11 fs is measured in a pump-probe experiment This duration is already enough to consider the observation of ultrafast chemical dynamics at the C K-edge[30,31,53,59]. Improved CEP stability and feedback control over the delay will allow attosecond transient absorption experiments in the SXR in the future
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