Round-robin absorption measurements of HR-coatings at 1064 nm

Absorption is a key parameter for optical materials and coatings in an increasing number of applications. Following the need for absorption measurements, a variety of different techniques have been established in the past 2 decades. Although all of them are very sensitive - allowing to measure down to the ppm absorption level – the absolute calibration remains a main challenge. For the first time to the best of our knowledge, we present data of a Round-Robin absorption test with a total of 11 participants using 5 different measurement techniques, including scientific institutes as well as companies. The subject of the test is the measurement of two highly reflective (HR) coatings (Bühler Alzenau GmbH) with different expected absorption levels at a wavelength around 1064nm. Besides a look on the overall absorption data scattering, the goals are comparing data obtained by identical test equipment at different locations as well as the influence of sample cleaning procedures. Additional CRD, total scattering, and residual transmission measurements provide information on the expected absorption data.