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.