Claire Poppett

Optical fiber systems for the BigBOSS instrument

We describe the fiber optics systems for use in BigBOSS, a proposed massively parallel multi-object spectrograph for the Kitt Peak Mayall 4-m telescope that will measure baryon acoustic oscillations to explore dark energy. BigBOSS will include 5,000 optical fibers each precisely actuator-positioned to collect an astronomical target’s flux at the telescope prime-focus. The fibers are to be routed 40m through the telescope facility to feed ten visible-band imaging spectrographs. We report on our fiber component development and performance measurement program. Results include the numerical modeling of focal ratio degradation (FRD), observations of actual fibers’ collimated and converging beam FRD, and observations of FRD from different types of fiber terminations, mechanical connectors, and fusion-splice connections.

The BigBOSS spectrograph

BigBOSS is a proposed ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the growth of structure with a 14,000 square degree galaxy and quasi-stellar object redshift survey. It consists of a 5,000- fiber-positioner focal plane feeding the spectrographs. The optical fibers are separated into ten 500 fiber slit heads at the entrance of ten identical spectrographs in a thermally insulated room. Each of the ten spectrographs has a spectral resolution (λ/Δλ) between 1500 and 4000 over a wavelength range from 360 - 980 nm. Each spectrograph uses two dichroic beam splitters to separate the spectrograph into three arms. It uses volume phase holographic (VPH) gratings for high efficiency and compactness. Each arm uses a 4096x4096 15 μm pixel charge coupled device (CCD) for the detector. We describe the requirements and current design of the BigBOSS spectrograph. Design trades (e.g. refractive versus reflective) and manufacturability are also discussed.

Design and production of DESI slit assemblies

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq. deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fibre optic positioners. The fibres in turn feed ten broad-band spectrographs. We describe the design, production, quality assurance procedures and performance of the DESI slit assemblies.

Fibre system of DESI

We describe the fiber system of the Dark Energy Spectroscopic Instrument (DESI). Its primary science goal is to provide a survey of 14,000 square degrees of the extragalactic sky using the Mayall 4m telescope in five years. The fibre system will provide a multiplex gain of 5000 so that more than 20 million galaxies can surveyed. Applying a number of tests to the survey dataset should allow the evolution of the equation of state of the universe to be determined to greater accuracy than before. The fibre system will provide a multiplex gain of 5000 with very high levels of performance.

Focal ratio degradation performance of fiber positioning technology used in the Dark Energy Spectroscopic Instrument (DESI)

The Dark Energy Spectroscopic Instrument (DESI) is a Stage IV ground-based dark energy experiment and will be used to conduct a five year survey covering 14,000 deg2 to z=3.5. This survey is accomplished using five thousand robotically positioned optical fibers that can be quickly reconfigured with a 5 μm positioning accuracy. The fiber performance in the near and far field of two types of robotic positioners are currently being investigated: tilting spine mechanical simulators and eccentric axis (or θ-φ) positioners. The far field performance of the fiber is important since the instrument efficiency is adversely affected if light from the fibers enters the spectrograph at a faster focal ratio than the spectrograph can accept (f/3.57 in the DESI design). This degradation of the focal ratio of light is caused by light entering the fiber off axis (tiliting positioner) or bending, twisting, and stress of the fiber (eccentric axis) positioner. The stability of the near field intensity distribution of the fiber is important since this determines the spectrograph point spread function (PSF). If the PSF changes from the calibration to the science exposures, this will result in an extraction bias. For DESI, a particular concern is the distortions in the PSF due to movement of the fibers during re-pointing.

Overview of the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We present an overview of the instrumentation, the main technical requirements and challenges, and the current status of the project.

Design and production of the DESI fibre cables

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryonic Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fibre optic positioners. The fibres in turn feed 10 broad-band spectrographs. We will describe the design and production progress on the fibre cables, strain relief system and preparation of the slit end. In contrast to former projects, the larger scale of production required for DESI requires teaming up with industry to find a solution to reduce the time scale of production as well as to minimise the stress on the optical fibres.

The DESI fiber system

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the design and performance of the DESI fiber system. This includes 5000 custom positioner fiber assemblies, spliced to 10 fiber cables terminated in a slit array.

Design, production and performance of the DESI front end fiber system

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the design and performance of the DESI fiber system which consists of 5000 custom positioner fiber assemblies that are installed into 5000 robotic fiber positioners.

The DESI slit design: science and calibration solutions

The Dark Energy Survey Instrument (DESI) is a 5000-fibre optical multi object spectrograph for the 4m Mayall telecope at the Kitt Peak National Observatory. Ten identical three channel spectrographs will be equipped with 500-element fibre slits. Here we focus on the architecture of the science slits and the interchangeable auxiliary slits required for calibration.