6.1.1 Design

FLITECAM consists of a cryogenically cooled near-IR (NIR) camera that can be used for both imaging and grism spectroscopy. A schematic of the optical bench is shown in Figure 6-1 with a full ray trace diagram in Figure 6-2. The incoming beam first passes through the entrance aperture and into the collimator assembly, a stack of custom designed lenses that allow imaging of nearly the entire 8'x8' SOFIA field of view (FOV). The beam is then repositioned using three flat fold-mirrors so that it passes through the image pupil and through a pair of 12-position filter wheels. A fourth flat fold-mirror redirects the beam through the f/4.7 refractive imaging assembly, which then focusses the beam on the array.

When observing in spectroscopy mode, only minimal changes to the optical path are required. First, the slit mask is inserted into the beam immediately behind the aperture window at the telescope focus. The slit is a single 16.5 mm long slit (2' on the detector) divided in half with two different widths, one approximately 2'' and the other 1''. Second, the chosen grism and order sorting filter, located in filter wheel #2 and #1, respectively, are set in place. Details are presented in Section 6.1.5 below.

Diagram of the front end of FLITECAM

Figure 6-1: This is a block diagram of the front end of the FLITECAM instrument with labels of important components.

Ray diagram for FLITECAM

Figure 6-2: This is the ray diagram for the FLITECAM instrument. The inset at the upper left displays the additional lenses inserted into the light path for the pupil-viewing mode.