Figure 3.

Optical laser (no beam) and X-ray fluorescence temperature of a 40 µm ruby crystal as a function of the cryostat set point. The X-ray beam size was uncollimated 20 µm × 20 µm, Gaussian with incident flux 3.18 × 10¹² and 1.19 × 10¹² photons s⁻¹ at 9.2 and 12.8 keV, respectively (as detailed in Section 2.1).