RMS thermal slope error and the maximum temperature of the ID06 LN2-cooled silicon crystal versus absorbed power. RMS values are calculated over the whole footprint or half footprint (_fp/2) length, from the slope distribution along the central axis or averaged (_av) over the transverse footprint width. The primary slits opening is 2 mm × 1 mm (H × V). The four points (a, b, c, d) correspond to the four heat load conditions shown in Fig. 9.