Cryogenic measurement of the optical absorption coefficient in sapphire crystals at 1.064 μm for the large-scale cryogenic gravitational wave telescope

Abstract We have applied laser calorimetry to the measurement of optical absorption in mono-crystalline sapphire at cryogenic temperatures. Sapphire is a promising candidate for the mirror substrates of the large-scale cryogenic gravitational wave telescope. The optical absorption coefficients of different sapphire samples at a wavelength of 1.064 μm at 5 K were found to average 90 ppm/cm.