Fig. 1.

Sketch of the XPCS experimental setup and some examples of speckles. (A) The coherent X-ray beam is produced at the PETRA III synchrotron storage ring, including the undulator (U), beamline optics, and compound refractive lenses (CRL). The MAXIPIX 2D pixel detector is fixed at the end of the 5-m-long detector arm, supplied by an evacuated flight tube. A series of high-resolution speckle patterns at ∼0.5° away from the exact 0 0 1 Bragg position was recorded as the sample temperature decreased. (B) The intensity distribution over the entire detector at 398 K. (C–E) Zoomed-in images of the selected areas in B showing the evolution of speckles within 2 K temperature range. The horizontal double arrows in B and C indicate the reciprocal space extension of the relevant detector segments.