  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.
