X-ray induced absorption of high-purity sapphire and investigation of the origin of the residual absorption at 1064 nm

We report a set of optical absorption measurements on x-irradiated high-pur ity sapphire. The results of the photothermal deflection absorption measure ments at 1064 nm show an increase of the absorption at the x-irradiated are as. The x-ray damage recovery is achieved through annealing, where the abso rption level at 1064 nm is brought from an average level of similar to 80 p pm cm(-1) to similar to 24 ppm cm(-1). UV-Vis spectroscopy results suggest that the residual absorption at 1064 nm is due to complex clusters of Ti an d Fe ions and oxygen vacancies. We suggest that a further reduction of Ti a nd Fe in sapphire (<0.1 ppm) as well as oxygen vacancies (through post grow th oxidizing annealing) would further reduce the absorption. Moreover, the absorption level of 20 ppm cm(-1) remains within the requirements of the se cond generation laser interferometric gravitational-wave detectors.