Beam characterization: application to the laser damage threshold

Abstract

ABSTRACT The laser damage threshold determination is linked to many factors as the damage criteria, the test conditions...Among them, the spatial beam characterization as well as the power or the energy in the beam plays a key role. Indeed, anappropriate value has to be assigned to each tested site. This number is important to certify a component or to compare the components. This paper is focused on determining the beam parameters for 2 kinds of laser damage. The first part addresses the peak fluence measurement on YAG laser damage test facilities. The proposed method is applied to stablelasers. Stable lasers mean the spatial profile (not the energy) is similar during the experiments. Before the laser damagetests, the spatial beam is visualized with a CCD camera. Then, the spatial beam profile is cautiously processed to extractthe relation between the peak fluence and the energy, which is easy to measure in real time. This method is illustrated at1064 nm. Finally, this procedure is validated on silicon wafer. Indeed, at 1064 nm, the theoretical laser damage thresholdof silicon wafer is well known. Furthermore, it is independent of the pulse length in the nanosecond regime. The secondpart will be shortly devoted to a more specific problem : the CW (continuous wave) damage threshold of CO2 mirrors. Ithas been previously shown that the short term threshold (typically