Double pass double etalon spectrometer

摘要

A first double pass etalon based spectrometer. In a preferred embodiment a second etalon matched to the first double pass etalon is used to produce extremely precise fringe data. Spectral components of a diffused beam are angularly separated as they are transmitted through an etalon. A retroreflector reflects the transmitted components back through the etalon. Twice transmitted spectral components are directed through a second etalon and focused onto a light detector which in a preferred embodiment is a photo diode array. The spectrometer is very compact producing the extremely precise fringe data permitting bandwidth measurements with precision needed for microlithography for both DELTAlambdFWHM and DELTAlambd95%.