Development of an infrared absorption measurement system for large aperture optics

Surface absorption defect has significant effects on the laser damage in the high power laser systems. Photothermal absorption measurement system based on the laser induced surface thermal lensing (STL) effect has been widely used in the research on the correlation between laser damage susceptibility and properties of weak absorption defects for small optical specimens. In this paper, we present the progress in the development of an automated measurement system for large aperture optics with a size around 400mm. The wavelength at 1064nm is used as the pump laser to investigate the absorption properties for the inspected site. The system which shows a measurement sensitivity of absorbance down to 0.1 ppm and measurement repeatability of 10% requires little special skills from the operators and is therefore more reliable and reproducible. The specific applications of the system include weak absorption measurement, local absorption defects detection as well as laser-coating-interaction dynamics monitoring. The high sensitive automated system proposed in this work is an effective diagnostic tool for the examination of large aperture optics with desired optical properties.