The grating from ZEUS will be transfered to ZEUS-2. All other optical elements are redesigned to maximize the usable field of view (FoV) within the limited instrument envelopes dictated by the CSO and APEX telescopes. The final optics are very similar in concept to those of ZEUS, but we increased the usable FoV from 83 arcsec in the original design to 155 arcsec (CSO values), we eliminated one mirror, and we enabled a larger tilt range for the grating. Figure 4 illustrates our design. The f/12 beam from the telescope enters the dewar window (made of HDPE), reaching a focus just inside the 3 K stage. It is then reflected off of flat mirror M1 onto collimating mirror M2 and through a Lyot stop to M3. The M2/M3 pair change the f/# of the system from 12 to 2.75, appropriate for the detector array. M3 focuses the light onto the entrance slit of the spectrometer, from which it then expands to fill the right half of the collimating mirror, M4. M4 creates a 10 cm collimated beam, which illuminates the 38 cm long grating. The dispersed light returns to the left side of M4, and then is reflected up to flat mirror M5 which sends the beam to the focal plane array.
- » Grating Properties:
- - R2 Echelle
- - L ~ 35 cm
- - 9th order 200 mm
- - 8th order 230 mm
- - 5th order 350 mm
- - 4th order 450 mm
- - 3th order 610 mm
Figure 4 - Optical ray trace of ZEUS-2.
Green and blue beams are spatial limits of Array 1.
Yellow and red beams are spatial limits for Array 2/3.