Cryogenic measurement of the optical absorption coefficient in sapphire crystals at 1.064(micro)m for the Large-scale Cryogenic Gravitational wave Telescope

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(micro)m at 5K were found to average 90ppm/cm.