A double-pass Sisam spectrometer for the near infrared

Abstract

A double-pass Sisam spectrometer of simplified design is described in which the two gratings rotate about a common axis. Sample spectra are given and the performance of the instrument is assessed and compared with that predicted theoretically. A resolution of 0.05 cm^-1 has been achieved at 1.6 µm, corresponding to 90% of the maximum theoretically attainable with the gratings and configuration used. This performance was maintained over a continuously scanned spectral range of 500 cm^-1 without realignment of the optical components. The instrument thus offers a real gain in signal-to-noise ratio over the equivalent, practical slit spectrometer of a factor of between 30 and 1000.