Our study aimed to identify surface laser damage mechanisms on non-linear crystal and develop processing technologies to enhance resistance to surface laser damage. Our research was motivated by a desire to increase the lifetime of crystal optics fielded in high-power/high-energy laser systems.
We demonstrated that surface laser damage on potassium dihydrogen phosphate (KDP), a commonly used frequency-converting crystal, can be caused by surface fractures and by redeposition of dissolved KDP during processing. We developed a novel processing fluid that exploits the water solubility to KDP and the nanoscale structure of microemulsions to controllably dissolve KDP surfaces. The development of a novel etching fluid showed that a viable pathway exists to passivating surface defects on KDP against laser damage. This fluid is unique in that in contains water, unlike other KDP-processing fluids, and that its structure-function properties can be controlled through compositional control. Etched fractures are more resistant to laser damage, but etching also reveals subsurface features left by the final finishing of the optic.
Our research determined, for the first time, that one of the most important conclusions drawn from decades of studies of laser damage to fused silica surfaces is transferable to KDP. Specifically, surface material removal is a powerful tool to increase surface laser damage resistance, provided redeposition can be avoided. Our insights and technology inform future efforts to improve crystal polishing and finishing technologies, possibly resulting in optics more resistant to the initiation and growth of laser damage on fielded laser systems.
Our work supports Lawrence Livermore National Laboratory's core competencies in lasers and optical science and technology. Our results advance the Laboratory's capabilities to make optics for high-power laser systems used in research for Livermore's mission areas.
Baxamusa, S., et al. 2018. "Novel Etching Fluids for Potassium Dihydrogen Phosphate." SPIE Laser Damage 10805. doi: 10.1117/12.2500297. LLNL-MI-761242.
——— . 2018. "Acoustic Activation of Water-in-Oil Microemulsions for Controlled Salt Dissolution." J. Colloid. Interf. Sci. 529. 366–374. doi: 10.1016/j.jcis.2018.06.032. LLNL-JRNL-750647.
——— . 2018. "Novel Etching Fluids for Water-sensitive Optical Crystals." SPIE Laser Damage, Boulder, CO, September 2018. LLNL-ABS-749625.
——— . 2019. "Novel Etching Fluids for Water-sensitive Optical Crystals." SPIE Laser Damage, Boulder, CO., September 2019. LLNL-CONF-772747.
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