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Register a new userDiffraction-limited integral-field spectroscopy for extreme adaptive optics systems with the Multi-Core fiber-fed Integral-Field Unit
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Direct imaging instruments have the spatial resolution to resolve exoplanets from their host star. This enables direct characterization of the exoplanets atmosphere, but most direct imaging instruments do not have spectrographs with high enough resolving power for detailed atmospheric characterization. We investigate the use of a single-mode diffraction-limited integral-field unit that is compact and easy to integrate into current and future direct imaging instruments for exoplanet characterization. This achieved by making use of recent progress in photonic manufacturing to create a single-mode fiber-fed image reformatter. The fiber-link is created with 3D printed lenses on top of a single-mode multi-core fiber that feeds an ultrafast laser inscribed photonic chip that reformats the fiber into a pseudo-slit. We then couple it to a first-order spectrograph with a triple stacked volume phase holographic grating for a high efficiency over a large bandwidth. The prototype system has had a successful first-light observing run at the 4.2 meter William Herschel Telescope. The measured on-sky resolving power is between 2500 and 3000, depending on the wavelength. With our observations we show that single-mode integral-field spectroscopy is a viable option for current and future exoplanet imaging instruments.
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A generic fiber positioning strategy and a fabrication path are presented for microlens-fiber-coupled integral field units. It is assumed that microlens-produced micro-images are carried to the spectrograph input through step-index,multi-mode fiber, but our results apply to micro-pupil reimaging applications as well. Considered are the performance trades between the filling percentage of the fiber core with the micro-image versus throughput and observing efficiency.A merit function is defined as the product of the transmission efficiency and the etendue loss. For a hexagonal packing of spatial elements, the merit function has been found to be maximized to 94% of an ideal fiber IFU merit value (which has zero transmission loss and does not increase the etendue) with a microlens-fiber alignment (centering) tolerance of 1 um RMS. The maximum acceptable relative tilt between the fiber and the microlens face has been analyzed through optical modeling and found to be 0.3 degree RMS for input f-ratio slower than f/3.5 but it is much more relaxed for faster beams. Several options of fabricating fiber holders have been compared to identify cost-effective solutions that deliver the desired fiber positioning accuracy. Femto-second laser-drilling methods deliver holes arrayed on plates with a position and diameter accuracy of 1.5 um RMS, and with an aspect ratio of 1:10. A commercial vendor produces plates with thickness of 5 mm, but with similar (1 um RMS) positioning accuracy. Both of these techniques are found to be moderately expensive. A purely photo-lithographic technique performed at WCAM (a facility at the University of Wisconsin, Madison), in tandem with deep reactive ion etching, has been used to produce a repeatable recipe with 100% yield. Photo-lithography is more precise (0.5 um RMS) in terms of hole positioning and similar diameter accuracy (1 um RMS).
We describe the design, manufacture, and performance of bare-fiber integral field units (IFUs) for the SDSS-IV survey MaNGA (Mapping Nearby Galaxies at APO) on the the Sloan 2.5 m telescope at Apache Point Observatory (APO). MaNGA is a luminosity-selected integral-field spectroscopic survey of 10,000 local galaxies covering 360-1030 nm at R ~ 2200. The IFUs have hexagonal dense packing of fibers with packing regularity of 3 um (RMS), and throughput of 96+/-0.5% from 350 nm to 1 um in the lab. Their sizes range from 19 to 127 fibers (3-7 hexagonal layers) using Polymicro FBP 120:132:150 um core:clad:buffer fibers to reach a fill fraction of 56%. High throughput (and low focal-ratio degradation) is achieved by maintaining the fiber cladding and buffer intact, ensuring excellent surface polish, and applying a multi-layer AR coating of the input and output surfaces. In operations on-sky, the IFUs show only an additional 2.3% FRD-related variability in throughput despite repeated mechanical stressing during plate plugging (however other losses are present). The IFUs achieve on-sky throughput 5% above the single-fiber feeds used in SDSS-III/BOSS, attributable to equivalent performance compared to single fibers and additional gains from the AR coating. The manufacturing process is geared toward mass-production of high-multiplex systems. The low-stress process involves a precision ferrule with hexagonal inner shape designed to lead inserted fibers to settle in a dense hexagonal pattern. The ferrule inner diameter is tapered at progressively shallower angles toward its tip and the final 2 mm are straight and only a few um larger than necessary to hold the desired number of fibers. This process scales to accommodate other fiber sizes and to IFUs with substantially larger fiber count. (Abridged)
[Abridged] Detecting cosmic ray hits (cosmics) in fiber-fed IFS data of single exposures is a challenging task, because of the complex signal recorded by IFS instruments. Existing detection algorithms are commonly found to be unreliable in the case of IFS data and the optimal parameter settings are usually unknown a-priori for a given dataset. The CALIFA survey generates hundreds of IFS datasets for which a reliable and robust detection algorithm for cosmics is required as an important part of the fully automatic CALIFA data reduction pipeline. We developed a novel algorithm, PyCosmic, which combines the edge-detection algorithm of L.A.Cosmic with a point-spread function convolution scheme. We generated mock data to compute the efficiency of different algorithms for a wide range of characteristic fibre-fed IFS datasets using the PMAS and VIMOS IFS instruments as representative cases. PyCosmic is the only algorithm that achieves an acceptable detection performance for CALIFA data. We find that PyCosmic is the most robust tool with a detection rate of >~90% and a false detection rate <5% for any of the tested IFS data. It has one less free parameter than the L.A.Cosmic algorithm. Only for strongly undersampled IFS data does L.A.Cosmic exceed the performance of PyCosmic by a few per cent. DCR never reaches the efficiency of the other two algorithms and should only be used if computational speed is a concern. Thus, PyCosmic appears to be the most versatile cosmics detection algorithm for IFS data. It is implemented in the new CALIFA data reduction pipeline as well as in recen
The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray spectrometer of the ESA Athena X-ray observatory. Over a field of view of 5 equivalent diameter, it will deliver X-ray spectra from 0.2 to 12 keV with a spectral resolution of 2.5 eV up to 7 keV on ~5 arcsecond pixels. The X-IFU is based on a large format array of super-conducting molybdenum-gold Transition Edge Sensors cooled at about 90 mK, each coupled with an absorber made of gold and bismuth with a pitch of 249 microns. A cryogenic anti-coincidence detector located underneath the prime TES array enables the non X-ray background to be reduced. A bath temperature of about 50 mK is obtained by a series of mechanical coolers combining 15K Pulse Tubes, 4K and 2K Joule-Thomson coolers which pre-cool a sub Kelvin cooler made of a 3He sorption cooler coupled with an Adiabatic Demagnetization Refrigerator. Frequency domain multiplexing enables to read out 40 pixels in one single channel. A photon interacting with an absorber leads to a current pulse, amplified by the readout electronics and whose shape is reconstructed on board to recover its energy with high accuracy. The defocusing capability offered by the Athena movable mirror assembly enables the X-IFU to observe the brightest X-ray sources of the sky (up to Crab-like intensities) by spreading the telescope point spread function over hundreds of pixels. Thus the X-IFU delivers low pile-up, high throughput (>50%), and typically 10 eV spectral resolution at 1 Crab intensities, i.e. a factor of 10 or more better than Silicon based X-ray detectors. In this paper, the current X-IFU baseline is presented, together with an assessment of its anticipated performance in terms of spectral resolution, background, and count rate capability. The X-IFU baseline configuration will be subject to a preliminary requirement review that is scheduled at the end of 2018.
In this article we present the integral field spectroscopy (IFS) wiki site, http://ifs.wikidot.com; what the wiki is, our motivation for creating it, and a short introduction to IFS. The IFS wiki is designed to be a central repository of information, tips, codes, tools, references, etc., regarding the whole subject of IFS, which is accessible and editable by the whole community. Currently the wiki contains a broad base of information covering topics from current and future integral field spectrographs, to observing, to data reduction and analysis techniques. We encourage everyone who wants to know more about IFS to look at this web-site, and any question you may have you can post from there. And if you have had any experience with IFS yourself, we encourage you to contribute your knowledge and help the site develop its full potential. Before re-inventing the wheel, consult the wiki...
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