Diamond Meta-Surfaces for High Power Laser Applications

Over the past decade optical quality CVD diamond has found its way into many high -power laser applications. In these demanding high -power applications, diamond is able to succeed due to its extraordinary physical properties. The highest thermal conductivity of any known material, low absorption over a broad spectrum, and exceptional strength all contribute towards an excellent optical material. As diamond is a high refractive index material, a solution is generally needed to manage Fresnel reflections from polished diamond surfaces. This is especially important for high -power laser applications, where even just a few percent of total power reflected must be carefully handled. Currently the industry standard solution is to apply thin film coatings to the polished diamond surfaces, and for many applications this is a perfectly adequate solution. In fact it has been shown that thin film coated diamond windows greatly outperform similar thin film coated windows [1]. For the most demanding and highest power density applications, applications that are pushing the boundaries of technology, thin film coatings can be a limitation. This is due to the relatively poor thermal properties of the coating materials; at high enough power -density the rate of heat generation through absorption overwhelms the ability of the coating to dissipate heat, leading to thermal runaway and often catastrophic failures. Laser Induced Damage Threshold (LIDT), a common measure of an optic's power handling capability, describes the power density at which this tipping point occurs. Thankfully nature has demonstrated an alternative solution towards eliminating reflections. Close inspection of the eyes of moths reveals a tightly packed array of conical structures on a sub -micron scale. In nature these tightly packed arrays eliminate reflections that otherwise may give the moth away to predators. Likewise, in demanding laser applications this "moth -eye" solution can be applied to eliminate Fresnel reflections. The advantage to this approach is that the LIDT of a moth -eye optic is limited by only the material properties of the optic itself, rather than by the material properties of a thin film coating. Given diamond's extraordinary material properties, the moth -eye approach is especially advantageous when creating a diamond optic.