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The Prime Focus Spectrograph (PFS) is an optical/near-infrared multi-fiber spectrograph with 2394 science fibers, which
are distributed in 1.3 degree diameter field of view at Subaru 8.2-meter telescope. The simultaneous wide wavelength
coverage from 0.38 μm to 1.26 μm, with the resolving power of 3000, strengthens its ability to target three main survey
programs: cosmology, Galactic archaeology, and galaxy/AGN evolution. A medium resolution mode with resolving
power of 5000 for 0.71 μm to 0.89 μm also will be available by simply exchanging dispersers. PFS takes the role for the
spectroscopic part of the Subaru Measurement of Images and Redshifts (SuMIRe) project, while Hyper Suprime-Cam
(HSC) works on the imaging part. HSC’s excellent image qualities have proven the high quality of the Wide Field
Corrector (WFC), which PFS shares with HSC. The PFS collaboration has succeeded in the project Preliminary Design
Review and is now in a phase of subsystem Critical Design Reviews and construction.
To transform the telescope plus WFC focal ratio, a 3-mm thick broad-band coated microlens is glued to each fiber tip.
The microlenses are molded glass, providing uniform lens dimensions and a variety of refractive-index selection. After
successful production of mechanical and optical samples, mass production is now complete. Following careful
investigations including Focal Ratio Degradation (FRD) measurements, a higher transmission fiber is selected for the
longest part of cable system, while one with a better FRD performance is selected for the fiber-positioner and fiber-slit
components, given the more frequent fiber movements and tightly curved structure. Each Fiber positioner consists of two
stages of piezo-electric rotary motors. Its engineering model has been produced and tested. After evaluating the statistics
of positioning accuracies, collision avoidance software, and interferences (if any) within/between electronics boards,
mass production will commence. Fiber positioning will be performed iteratively by taking an image of artificially back-illuminated
fibers with the Metrology camera located in the Cassegrain container. The camera is carefully designed so
that fiber position measurements are unaffected by small amounts of high special-frequency inaccuracies in WFC lens
surface shapes.
Target light carried through the fiber system reaches one of four identical fast-Schmidt spectrograph modules, each with
three arms. All optical glass blanks are now being polished. Prototype VPH gratings have been optically tested. CCD
production is complete, with standard fully-depleted CCDs for red arms and more-challenging thinner fully-depleted
CCDs with blue-optimized coating for blue arms. The active damping system against cooler vibration has been proven to
work as predicted, and spectrographs have been designed to avoid small possible residual resonances.
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