shown in Figure 2. Software Design Ideas,
and staff from the Australian National Uni-
versity, provided software support during
this effort.
This work bought the fiber system, Slit View-
er Assembly, and spectrograph together for
the first time.
The fiber system, which sits between the
Cassegrain Unit and the Slit Viewer Assembly,
includes the following components:
•
62 individual fibers that connect the
Cassegrain Unit to the Slit Viewer Assembly.
• The microlens IFU units that consist of two
low-resolution arrays and one high-resolu-
tion array, each with a separate array for sky.
• A flexible conduit for the optical cable that
minimizes stress on the fibers, thereby re-
ducing Focal-Ratio Degradation.
• Spectrograph slit optics that form a slit
from each object. The slits are 1 microlens
wide and either 7 or 19 microlenses long
in the standard- or high-resolution modes,
respectively.
• An acquisition and guiding slit.
• A simultaneous wavelength calibration
light injection port.
The fiber system also includes two associated
devices: (1) a mode-scrambling, noise-reduc-
ing agitator that creates variable conditions
for propagation of light in all of the optical fi-
bers; and (2) a calibrator that is the reference
source for simultaneous wavelength calibra-
tion via a Thorium-Xenon lamp.
The Slit Viewer Assembly uses a beam splitter
to direct 99% of the slit output to the spec-
trograph and 1% to the slit imaging system. It
also removes the need for an on-instrument
wavefront sensor for flexure compensation,
with the telescope’s peripheral wavefront
sensor being used for fast tip/tilt and focus
corrections.
July 2019
The spectrograph subsystem is a gravity-
stable asymmetric white-pupil échelle spec-
trograph, with two arms and volume-phase
holographic grating cross-dispersers. It com-
prises the following key elements: Figure 2.
• An optical table that maintains spectrograph
stability and provides thermal mass for the
environmental enclosure sub-system. Credit Tony Farrell
Image of spectrum
captured from the
location where the
GHOST blue detector will
be positioned.
• A Slit Viewer Assembly unit, discussed
above, that directs 99% of the light from
the slit to the collimator.
• A collimator mirror that collimates the
beam from the Slit Viewer Assembly and
directs it to the échelle grating.
• An échelle grating that disperses the light
into the échelle orders.
• Two transfer mirrors: one convex fold mir-
ror and the white pupil relay mirror. The
transfer mirrors and the collimator mirror
together form the white pupil relay that
reimages the pupil of the dispersed light
at the échelle onto the Volume Phase Holo-
graphic gratings.
GeminiFocus
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