 The light source delivers monochromatic, usually polarized, focused, high-intensity photon beam (~1012 photons/s) to the sample.They range from compact noble-gas discharge UV lamps and radio-frequency plasma sources (10–⁠40 eV), UV lasers (5–⁠11 eV) to synchrotron insertion devices optimized for different parts of the EM spectrum (10 eV in the ultraviolet to 1000 eV X-rays).The sample holder accommodates the samples of crystalline materials whose electronic properties are to be investigated.