Heating of optical elements exposed to intense x-rays inspected by NIR thermal camera

Facilities such as synchrotrons and free-electron lasers represent ultrabright sources of short-wavelength radiation. Intense x-ray pulses generated at a high repetition rate can cause severe damage to optical elements used for beam guiding, splitting and focusing. Numerous thermal and non-thermal processes can be responsible for irreversible changes. Also, even reversible photo-thermal changes can affect a functionality of x-ray optics in an undesirable manner. For an estimation of the thermo-mechanical damage risk, a thermalized fraction of absorbed radiation energy should be determined. In the present study, NIR thermal camera was used for monitoring of a temperature on surfaces of selected optical elements heated by trains of ultra-short x-ray laser pulses at the European XFEL facility. Earlier, synchrotron-radiation heated Ge beam splitter was inspected using the same camera at ESRF. Understanding thermal behaviour of different elemental solids exposed to intense x-ray radiation can help to find conditions under which x-ray optical systems can be operated at those facilities without any risk of irreversible damage or even just a temporary loss of their full functionality.