This is the output of the PIFS in high-resolution spectral mode, using a collimated Helium-Neon laser beam as the input. The input beam is split into these eight slits, then spectrally dispersed. This image is an actual 6th order spectrum of the HeNe laser, not just a slit image. There are pencil marks on the paper showing roughly where the light was expected to fall. The stair-stepped appearance is a natural consequence of the image slicer geometry. The overall outline reflects the size and position of the infrared detector array in the final configuration.
Next Picture (Flip mirrors in dewar)