We present the as-built design overview and post-installation performance of the upgraded WIYN Bench Spectrograph.
This Bench is currently fed by either of the general-use multi-fiber instruments at the WIYN 3.5m telescope on Kitt
Peak, the Hydra multi-object positioner, and the SparsePak integral field unit (IFU). It is very versatile, and can be
configured to accommodate low-order, echelle, and volume phase holographic gratings. The overarching goal of the
upgrade was to increase the average spectrograph throughput by ~60% while minimizing resolution loss (< 20%). In
order to accomplish these goals, the project has had three major thrusts: (1) a new CCD was provided with a nearly
constant 30% increase is throughput over 320-1000 nm; (2) two Volume Phase Holographic (VPH) gratings were
delivered; and (3) installed a new all-refractive collimator that properly matches the output fiber irradiance (EE90) and
optimizes pupil placement. Initial analysis of commissioning data indicates that the total throughput of the system has
increased 50-70% using the 600 l/mm surface ruled grating, indicating that the upgrade has achieved its goal.
Furthermore, it has been demonstrated that overall image resolution meets the requirement of <20% loss.
The WIYN One Degree Imager (ODI) will provide a one degree field of view for the WIYN 3.5 m telescope located on Kitt Peak near Tucson, Arizona. Its focal plane will consist of an 8x8 grid of Orthogonal Transfer Array (OTA) CCD detectors with nearly one billion pixels. The implementation of these detectors into the focal plane has required the development of several novel packaging and characterization techniques, which are the subject of this paper. We describe a new packaging/hybridization method in which the CCD die are directly bonded to aluminum nitride ceramic substrates which have indium bump on one side and brazed pins on the other. These custom packages allow good thermal conductivity, a flat imaging surface, four side buttability, and in situ testing of the devices during backside processing. We describe these carriers and the backside processing techniques used with them. We have also modified our cold probing system to screen these OTA die at wafer level to select the best candidates for backside processing. We describe these modifications and characterization results from several wafer lots.
The main advantage of the WIYN One Degree Imager (ODI) over other wide-field imagers will be its exceptional image quality. The fine pixel scale (0.11") provides uncompromised sampling of stellar PSFs under most conditions (seeing >0.3"). The telescope routinely delivers the site seeing (median ~ 0.7") which is often below 0.5" FWHM, and can be as low as 0.25". The ODI specifications require the optics to maintain native high quality images. A two-element, fused silica, corrector meets the geometric error budget of 0.10" images, but the first element requires a mildly aspheric surface. The other element serves as the dewar window. A pair of cemented prisms (fused silica plus PBL6Y) serve as an ADC, which is essential to meet the image quality requirements for many observing programs. We describe the optical design details and its performance, the tolerances required, and the trade-offs considered for anti-reflection coatings. This paper is an update to a preliminary three-element design.
We describe the redesign and upgrade of the versatile fiber-fed Bench Spectrograph on the WIYN 3.5m telescope. The
spectrograph is fed by either the Hydra multi-object positioner or integral-field units (IFUs) at two other ports, and can
be configured with an adjustable camera-collimator angle to use low-order and echelle gratings. The upgrade, including
a new collimator, charge-coupled device (CCD) and modern controller, and volume-phase holographic gratings
(VPHG), has high performance-to-cost ratio by combining new technology with a system reconfiguration that optimizes
throughput while utilizing as much of the existing instrument as possible. A faster, all-refractive collimator enhances
throughput by 60%, nearly eliminates the slit-function due to vignetting, and improves image quality to maintain
instrumental resolution. Two VPH gratings deliver twice the diffraction efficiency of existing surface-relief gratings: A
740 l/mm grating (float-glass and post-polished) used in 1st and 2nd-order, and a large 3300 l/mm grating (spectral
resolution comparable to the R2 echelle). The combination of collimator, high-quantum efficiency (QE) CCD, and VPH
gratings yields throughput gain-factors of up to 3.5.