ESPRESSO is a fiber feed ultrastable High Resolution Spectrograph designed to work in the Combined-Coudé focus of Very Large Telescopes (VLT). A high resolution (R~100000) and an ultra-high resolution (R~220000) mode will be available to collect the light coming of one VLT telescope. In addition, ESPRESSO has an observing mode which allows to collect light of 2, 3 or 4 VLT units. This mode can feed simultaneously the spectrograph using a 4x1 fiber combiner. In the combiner, the light from 4 octagonal fibers will be mixed when projected onto a square fiber, as a double scrambler device. Here it is presented the design, manufacture, integration and tests for the 4x1 combiner of the ESPRESSO Fiber Link.
The optical instrument used to measure and characterize sky quality at the IAC observatories is the DIMM (differential image motion measurements). The optical system and its mode of operation are relatively simple. It consists, basically, placing two equal apertures at the entrance of a telescope, in one of them an optical wedge is located. In this way, two beams of the same object are obtained which will lead to two on the focal plane of the telescope but laterally separated a few seconds arc. The complexity of this optical system lies in the "simplicity" of the plate used to separate the beams, it is a flat-faced wedge of a few minutes, and this is where problems arise when manufacturing it.<p> </p> In this paper we present a new optical system concept to separate the beams. This is done using two optical flats tilted. The optical flats are not placed at the entrance of the telescope, but in the convergent beam. The optical design, manufacture and the test results obtained are presented.
Here is presented the tests results and the lessons learnt concerning an opto-mechanical device to scan the GREGOR telescope field of view. The scanning is done by means of a set of mirrors and a mechanism which allows to keep the optical path length constant, regardless the portion of the field being scanned. This system is intended to feed a static image slicer used for solar observations. The tight level of tolerances required makes its design and tests a real challenging activity which produces a lot of unexpected lessons to learn. The story after the issues detection, the consequent root cause analysis, the additional tests and tools developed to study the phenomena, and the construction of the solutions and issue mitigation mechanisms provides a good background to elaborate some recommendations for future developments.
Pierced mirrors are used in high resolution and ultrastable spectrographs to feed guiding cameras and to improve the target stability. This paper describes the concept, design, manufacture, test and integration of ESPRESSO pierced mirrors which are part of the Fiber Link subsystem. ESPRESSO is a spectrograph located in the Coude Laboratory of VLT that can be feed by the light of any VLT telescope. Similar mirrors will be used in the Fiber Link subsystem of NIRSP spectrograph which is an Infrared spectrograph for the 3.6 m telescope of the Silla Observatory.
We present the commissioning of an IFU based on image-slicers and a 2D-Field-of-View Scanning System (FoV-SS) for the GREGOR Infrared Spectrograph (GRIS). The prototype of the image-slicer has eight slices of 1.8 mm x 0.1 mm in Zerodur, covering an area of 20 arcsec<sup>2</sup>. The FoV-SS, equipped with three Degrees of Freedom (DoF), allows to scan a region of 1 arcmin<sup>2</sup>, feeding the image-slicer with different portions of the field of view. A batch of tests was done during the Assembly, Integration and Verification (AIV) at GREGOR telescope.
An image slicer has been proposed for the Integral Field Spectrograph  of the 4-m European Solar Telescope (<i>EST</i>)  The image slicer for <i>EST</i> is called <i>MuSICa</i> (Multi-Slit Image slicer based on collimator-Camera)  and it is a telecentric system with diffraction limited optical quality offering the possibility to obtain high resolution Integral Field Solar Spectroscopy or Spectro-polarimetry by coupling a polarimeter after the generated slit (or slits). Considering the technical complexity of the proposed Integral Field Unit (<i>IFU</i>), a prototype has been designed for the <i>GRIS </i>spectrograph at <i>GREGOR</i> telescope at Teide Observatory (Tenerife), composed by the optical elements of the image slicer itself, a scanning system (to cover a larger field of view with sequential adjacent measurements) and an appropriate re-imaging system. All these subsystems are placed in a bench, specially designed to facilitate their alignment, integration and verification, and their easy installation in front of the spectrograph. This communication describes the opto-mechanical solution adopted to upgrade <i>GRIS</i> while ensuring repeatability between the observational modes, <i>IFU</i> and long-slit. Results from several tests which have been performed to validate the opto-mechanical prototypes are also presented.
Cryostats are closed chambers that hinder the monitoring of materials, structures or systems installed therein. This paper presents a webcam-based measurement and monitoring system, which can operate under vacuum and cryogenic conditions to be mainly used in astrophysical applications. The system can be configured in two different assemblies: wide field that can be used for mechanism monitoring and narrow field, especially useful in cryogenic precision measurements with a resolution up to 4 microns/pixel.
The High Optical Resolution Spectrograph (HORS) is a proposed high-resolution spectrograph for the
10-m Gran Telescopio Canarias (GTC) based on components from UES, a spectrograph which was in
use at the 4.2-m William Herschel Telescope (WHT) between 1992 and 2001.
HORS is designed as a cross-dispersed echelle spectrograph to observe in the range 380-800 nm with
a FWHM resolving power of about 50,000. HORS would operate on the GTC as a general-purpose
high-resolution spectrograph, and it would serve as a test-bed for some of the technologies proposed
for ESPRESSO – an ultra-high stability spectrograph planned for the Very Large Telescope (VLT) of
the European Southern Observatory.
The HORS spectrograph will be placed in the Coudé room, where it can enjoy excellent thermal and
mechanical stability, fiber fed from the Nasmyth focus, which is shared with OSIRIS. Inside the
spectrograph, incoming light will hit a small folder mirror before reaching the collimator. After a
second folder, the light will go through a set of three prisms and an Echelle grating before entering the
spectrograph camera and, finally, reaching the detector.
This manuscript contains a summary of the whole process that has transformed UES into HORS, with
all the mechanical and optical modifications that have been introduced to reach the final layout.
HARMONI is a visible and near-IR integral field spectrograph, providing the E-ELT's spectroscopic capability at first
light. It obtains simultaneous spectra of 32000 spaxels, at a range of resolving powers from R~4000 to R~20000,
covering the wavelength range from 0.47 to 2.45 μm. The 256 × 128 spaxel field of view has four different plate scales,
with the coarsest scale (40 mas) providing a 5″ × 10″ FoV, while the finest scale is a factor of 10 finer (4mas).
We describe the opto-mechanical design of HARMONI, prior to the start of preliminary design, including the main subsystems
- namely the image de-rotator, the scale-changing optics, the splitting and slicing optics, and the spectrographs.
We also present the secondary guiding system, the pupil imaging optics, the field and pupil stops, the natural guide star
wavefront sensor, and the calibration unit.
This communication reviews the participation of the Instituto de Astrofísica de Canarias (IAC) in the design of the
European Solar Telescope. Apart of being the coordinator institution of the whole project, and, as such, responsible for
the project managing, the IAC leads several tasks like overall instrument definition or characterization of the
atmospheric turbulence profile with height or the definition of adequate detectors. More in particular, the IAC will
design and build two long-base SHABAR (SHAdow BAnd Ranger), instruments to measure medium-altitude seeing.
The IAC is also responsible for the design, together with other institutions, of the design of grating spectropolarimeters
suitable for multiwavelength high spatial and spectral resolution.
We have been testing at laboratory commercial variable attenuators commonly used in telecommunication applications
for their used in astronomy. Such variable attenuators are going to be included in the central fibers
of the integral field unit (IFU) of the prototype instrument EDiFiSE (Equalized and Diffraction-limited Field
Spectrograph Experiment). The EDiFiSE IFU is conformed by a lenslet array of 331 lenses, 331 fibers and seven
variable attenuators (inserted in the seven central fibers of the bundle). We present here the characterization of
the attenuator devices tested for their use in astronomy and, in particular, to their application in the observation
of object of large dynamic range using equalized integral field spectroscopy. We also present the optical tests we
have carried out to characterize the performances of two lenslet arrays acquired in the framework of the EDiFiSE
We present EDiFiSE, a prototype instrument for the observation of high-contrast systems, combining an adaptive
optics (AO) system and an equalized integral field unit (EIFU). The design of the AO system takes into account
the statistical behaviour of the atmospheric turbulence structure at the Canary Islands (Spain) astronomical
observatories: Roque de los Muchachos (ORM) on the island of La Palma and Teide observatory (OT) in
Tenerife. The AO will have the capability of adapting to the prevailing turbulence conditions; in this sense,
the EDiFiSE AO unit will be an 'adaptable' adaptive optics system. The corrected beam feeds an hexagonal
integral field unit formed by 331 micro-lenslets, which focus the intensity distribution at the focal plane into 331
optical fibers. The central seven fibers of the bundle include variable attenuators for the equalization of these
fibers output intensities, matching them to the dynamical range of the detector and reducing the optical cross
talk inside the spectrograph. This technique, called equalized integral field spectroscopy (Arribas, Mediavilla &
Fuensalida 1998<sup>1</sup>), permits to obtain spectral and spatial information of the equalized object and its surroundings
as well as accurate relative photometry and astrometry.
A theoretical design and experimental realization of multi-layer mirrors for Fabry-Perot interferometry and optical telecommunications is described in this work. The mirrors were designed and fabricated by 13 successive thin layers to achieve very high reflectance at optical wavelengths around 1300 nm. Thin layers are ZnS y MgF<sub>2</sub> presenting high and low refractive index respectively. Layer thickness are of λ<sub>o</sub>/2 at λ<sub>o</sub> = 656 nm. Experimental results include the characterization of the transmittance of mirrors around 1300 nm. Additionally the mirrors were integrated in a Fabry-Perot interferometer to characterize optical sources emitting at 1300 nm. Finally to show a practical application, optical phase modulation was analyzed, using the fabricated mirrors.