Fig. 10.

Comparison of optical throughput efficiency (a) and spectral resolution (b) as functions of entrance slit width for transmission spectrometer. The theoretical maximum optical transmission is shown as a dotted line in (a). As expected, a wider slit allows more light but also increases the FWHM of spectral features. The 28.7 micron slit was selected for flight. Although not shown in the figure (the lowest-wavelength Ne line used was at 576 nm), this slit just meets the $12{\text{cm}}^{-1}$ resolution requirement at the short-wavenumber end of the spectrum