Fig. 2: Intensity-dependent processes in the harmonic region.
From: Surface structure of water from soft X-ray second harmonic generation
A The harmonic produced by the XFEL is attenuated by intrinsic linear absorption through the water jet and a transient absorption (TA) induced by the fundamental. The SHG process produces additional counts in the harmonic region. B Difference signals for 550 eV at selected binned fundamental pulse energies (μJ). Colored shaded areas represent standard errors for the signal between three datasets. The blue and red dashed curves are the XFEL harmonic and squared fundamental spectra respectively. C Depiction of the intensity-dependent difference signals using the features in (A), reproducing (B). D Experimental covariance difference map for 550 eV showing intensity-dependent features. E Modeled best-fit covariance map with the intensity-dependent features from (A) indicated. The correlated positive SHG feature and negative TA background are apparent. Color bar magnitude is arbitrary but shared.
