Anti-reflection coatings for spectrometers with large spectral ranges

It is common for spectrometers to cover large spectral ranges with a single focal plane. It is difficult or impossible to strongly suppress reflections with a single coating stack. Abutting short and long wavelengths coatings is expensive, and the performance can still be insufficient. We discuss a novel structure that comprises a single layer whose thickness varies along the length of the dispersed spectrum. Such a coating has high performance, is inexpensive, and has large fabrication tolerances. We further report on measurements of the performance of one such optic. Extensions of the concept are discussed.