A Single-Double Pass Sisam Spectrometer for the Near Infrared

A double-pass Sisam spectrometer of high resolution and sensitivity, previously described, has been modified for single-pass operation. For discrete line emission sources, this modification provides a gain of a factor of 6 in sensitivity at the expense of a loss of a factor of 2 in resolution in the near infra red region. As is demonstrated, the modified instrument is particularly suitable for the study of weak spectral sources. A coherent modulation system has also been incorporated which eliminates the periodic variations in signal strength arising from the non-coherent modulation technique previously employed.