Fig. 5: X-ray speckle contrast obtained by maximum-likelihood estimation.

At Q = 2.00 ± 0.06 Å−1 with (circles) Ifixed < 3 µJ, (squares) 3 µJ < Ifixed < 5 µJ, (triangles) 5 µJ < Ifixed < 7 µJ, and (crosses) Ifixed > 7 µJ. (diamonds). The solid line represents the contrast measured when there was no overlap between two sub-pulses. The uncertainty was calculated using the second derivative of the log-likelihood based on the approach in ref. 20, and the uncertainty for the solid line is represented by the shade. The dashed line represents the decaying behavior48,49, which are estimated by the result of inelastic X-ray scattering where their amplitude was set by the XSVS result at Δt  = 0.