FIG. 10.

Effect of photon-energy jitter on SRIXS measurements. (a) Example of a pair of two-color incoming SASE pulses $I(\omega ,0)$ with a relative energy difference (jitter) of 3 eV: both the pump and the dump frequencies shift by the same amount with a jitter of the electron-beam energy of the accelerator. (b) 2000 simulated SRIXS spectra in logarithmic scale normalized by the averaged pump intensity $\text{log}(I(\omega ))/{\overline{I}}_p,\hspace{0.17em}{\overline{I}}_p=6.5\times {10}^{16}$ W/cm² as a function of central photon energy of the pump component, which was varied by ±4 eV. (c) Covariance map C_T of Eq. (12) accounting for the pulse energy jitter. The vibrational fine structure at ${\omega }_d=525-526$ eV and ${\omega }_p=533-534$ eV (see Fig. 7(c)) is lost due to the neighboring strong features reflecting pulse energy jitter. The pulse parameters are adapted from the recent experiment:³⁴ $N_p={10}^{12},\hspace{0.17em}{N}_d={10}^{11}$ photons, pulse duration is 100 fs, and z = 5 mm.