A journey from ancient China bronze mirrors to picometer shaped interference coatings
The basic form of a mirror as a cast metal object, with a highly polished reflective surface and relief decorations at the back, has remained unchanged throughout most of China's history. The earliest known Chinese mirrors date back to approximately 2000 BC. For almost a hundred years, advancements in the broad area of optical coatings have been used to shape mirror reflectivity in an inconceivable manner. For example, mirrors for deep ultraviolet (193 nm) and extreme ultraviolet (13.5 nm) are considered, playing a positive effect in lithography. Substantial improvements are expected in the efficiency of layer systems with regard to both optical performance and overall stability.