== Concern on mirror optical losses by H.Yamamoto ==

 * Scattering loss of 45ppm by low-freq (>1mm) surface error of 1nm RMS (25ppm with 0.75nm RMS).
 * Scattering loss of 6ppm by high-freq (<1mm) surface error of 0.2nm RMS.
 * Unexplainable point scattering loss of 10ppm (realistic estimate would be 15-30ppm).

These alone would make the total scattering loss already '''61ppm''' (with 1nm LF RMS) or 41ppm (with 0.75nm LF RMS).

 * Besides, absorption at the coatings, 0.5ppm based on the LMA coating on Silica substrate, can easily go worse by several ppm by contamination.
 * LF RMS could be improved if we spend enough money and time. LIGO set the requirement to be RMS<0.5nm and Tinsley has achieved that value.