Going Deeper into Laser Damage: Experiments and Methods for Characterizing Materials in High Power Laser Systems

Laser damage is a primary limiting factor to the design of high-power laser systems. This is true for short-pulse systems as well as long-pulse and continuous-wave (CW) systems. Unlike short-pulse laser damage, CW laser damage has been much less studied. This work comprises a background of laser damage and laser heating theory, a CW laser damage experiment and an imaging technique for monitoring laser heating. The damage experiment was performed on 100 nm thick hafnia coatings deposited on fused silica. Uniformly grown films were compared to hafnia-alumina nanolaminates. While the nanolaminates are known to perform better for 1 ns pulses, we found they had worse laser damage performance in the CW regime. We found the nanolaminates reduced crystallinity. The polycrystalline uniform films are thought to have increased absorption. We measured the thermal conductivity of the nanolaminates to be approximately 1/2 that of the uniform films. A theoretical model including the absorption and thermal conductivity of the nanolaminate and uniform film agreed with the experimental data for 1 ns pulses and CW tests. During laser damage experiments, anomalous damage morphologies were observed that we were unable to explain with theoretical techniques. We then developed an experimental method to observe high-speed laser damage events at the ms time-scale. We imaged laser heating and compared it to a theoretical model with good agreement. Our measurement method captured image data from a Mach- Zender interferometer that had do be processed ex-situ. We desired a system capable of providing real-time thermal data. We developed an image processing technique at least 66 times faster than the original method.