With the ever-increasing laser power and repetition rate, thermal control of laser media is becoming increasingly important. Except for widely used air cooling or a bonded heat sink, water cooling of a laser medium is more effective in removing waste heat. However, how to protect deliquescent laser media from water erosion is a challenging issue. Here, novel waterproof coatings were proposed to shield Nd:Glass from water erosion. After clarifying the dependence of the waterproof property of single layers on their microstructures and pore characteristics, nanocomposites that dope SiO2 in HfO2 were synthesized using an ion-assisted co-evaporation process to solve the issue of a lack of a high-index material that simultaneously has a dense amorphous microstructure and wide bandgap. Hf0.7Si0.3O2/SiO2 multifunctional coatings were finally shown to possess an excellent waterproof property, high laser-induced damage threshold (LIDT) and good spectral performance, which can be used as the enabling components for thermal control in high-power laser cavities.
Contamination plays a major role in lifetime of vacuum optics. Several efforts have been made to derive suitable models for lifetime prediction in laser-induced contamination related optical breakdown. But the broad spectrum of potential contaminants present in the various applications with their very specific contamination mechanisms complicates the derivation of universal optics degradation models.As one possible contamination initiation process, the impact of optical absorption on the laser-induced contamination and resulting optical breakdown is studied in this work. A set of specifically prepared samples using nanometer sized gold particles embedded in dense IBS anti-reflecting coatings is exposed to radiation of 355nm in low pressure naphthalene atmosphere. Even though the artificial defects are not in direct contact with the contaminant, their influence on the long-term optics performance in dependence on the particle concentration in the coating is evident. In the presence of naphthalene, the artificial nano-defects cause a significantly accelerated degradation compared to reference samples without those defects or in absence of the contaminant. For this specific type of contaminant, a correlation of the optical absorption and long-term durability is derived.
In order to enhance the reliability and performance of space-based Lidar systems, it is desirable to increase the damage resistance of ultraviolet antireflective coatings. For laser pulses with nanosecond pulse duration, laser-induced damage is known to be triggered by nano-sized defects embedded in the optical coating. In this work, we demonstrate the mitigation of damage precursors during the manufacturing of ion-beam sputtered (IBS) coatings using two approaches: ion bombardment with a secondary ion source and laser irradiation with a nanosecond-pulsed laser. Optical coatings produced with both technologies show a significantly increased damage threshold when tested in large-area raster scans.
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