Low absorption, anti reflection coatings are critical to the performance, reliability and lifetime of optics used is high power fiber lasers. High-power kilowatt-level fiber lasers operating between 1.0 and 1.1 µm find frequent use in macro-materials processing applications, such as cutting and welding metal sheets. The nature of these applications requires laser optics to perform properly at correspondingly high laser powers and power density levels. Minimizing losses due to absorption is therefore of crucial importance to laser reliability and performance. Achieving this requires a clearer understanding of the materials, coating technologies, and measurement techniques used for the manufacturer of high-performance, low-absorption fiber laser optics.