Precursors generated by fused silica during high-energy laser exposure are known to increase damage initiations on nearby fused silica surfaces, on which they are thought to adsorb. These precursors are of concern to increasing the laser energy in the final optics of the Lawrence Livermore National Laboratory (LLNL) National Ignition Facility (NIF). In this work, precursors were generated by exposing a fused silica sample with a single 3ω, 5 ns, 35 mm-diameter laser shot at approximately 12 J/cm2 average fluence in the presence of identical, witness samples not exposed to laser light in a precision cleaned test chamber. Five tests were conducted, one for each of five pressures: 760, 350, 10, 2.5, and 10-5 torr, using the LLNL Optical Sciences Laser Laboratory. The witness samples were then damage tested with a single laser shot: 3ω, 5 ns, 10 mm-diameter, and 26 J/cm2 average fluence to evaluate the effect of the different environmental pressures. The results of this experiment show that laser exposures in ambient pressure above 350 torr resulted in less observed laser-induced damage presumably due to suppression of precursor generation or inhibition of precursor transport. A detailed analysis of the fluence, damage and correlation to environmental pressure will be shown in this work. These results inform potential damage-reduction solutions for NIF final optics for future operation at higher power and energy and may be relevant to other high energy UV fused silica-based laser optical systems.
We present a technique for high-speed imaging of the dynamic thermal deformation of transparent substrates under high-power laser irradiation. Traditional thermal sensor arrays are not fast enough to capture thermal decay events. Our system adapts a Mach-Zender interferometer, along with a high-speed camera to capture phase images on sub-millisecond time-scales. These phase images are related to temperature by thermal expansion effects and by the change of refractive index with temperature. High power continuous-wave and long-pulse laser damage often hinges on thermal phenomena rather than the field-induced effects of ultra-short pulse lasers. Our system was able to measure such phenomena. We were able to record 2D videos of 1 ms thermal deformation waves, with 6 frames per wave, from a 100 ns, 10 mJ Q-switched Nd:YAG laser incident on a yttria-coated glass slide. We recorded thermal deformation waves with peak temperatures on the order of 100 degrees Celsius during non-destructive testing.
The surface damage morphologies produced by continuous-wave laser irradiation of coated optics were measured and
analyzed. A few laser damage morphologies were observed to be bull’s-eye patterns. It is noted that the bull’s-eye
pattern has some similarities to Bessel distributions of the form found in solutions of basic heat transfer or surface
acoustic wave problems, which may indicate a relationship. If these morphologies are truly thermal phenomenon, then
the Bessel ring diameter would be a function of thermal diffusivity. This might indicate that the ring diameter could be
used to assess the resistance of a film to laser damage.
3D Meta-Optics are optical components that are based on the engineering of the electromagnetic fields in 3D dielectric
structures. The results of which will provide a class of transformational optical components that can be integrated at all
levels throughout a High Energy Laser system. This paper will address a number of optical components based on 2D
and 3D micro and nano-scale structures and their performance when exposed to high power lasers. Specifically, results
will be presented for 1550 nm and 2000 nm spectral bands and power densities greater than100 kW/cm2.
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