FIG. 2.

(a) Dependence of the pump $I_p(\omega ,z)$ (right) and dump $I_d(\omega ,z)$ (left) spectra on propagation length for the strong pump regime ($N_p(0)={10}^{12},\hspace{0.17em}{N}_d(0)={10}^{10}$ photons per pulse, pulse duration is 100 fs). The spectral profiles at various propagation distances z are averaged over 4000 individual SASE shots. The spectra are normalized to the maximum of the incoming intensities. (b) Relative change in spectral intensity ${\alpha }_i({\omega }_i)=[I_i({\omega }_i,z)e^{{\sigma }_{\mathit{p}\mathit{h}}Nz}/I_i({\omega }_i,0)-1]$ at z = 5 mm for the dump ω_d (left) and pump ω_p (right) field, respectively.