The warm calibration unit (WCU) is one subsystem of the future METIS instrument on the European Extremely Large Telescope (E-ELT). Operating at daytime temperature, the WCU is mounted above the main cryostat of METIS and will be employed as calibration reference for science observations, as well as for verification and alignment purposes during the AIT phase. The WCU is designed and constructed at the University of Cologne, partner in the METIS consortium. The WCU, together with the full METIS instrument, went recently through a successful preliminary design review (PDR) phase at ESO and is entering now the Phase C of the project. In this paper, we present the current status of the WCU and summarize the mostly mechanical and optical engineering work. We adopted a hexapod unit to interface with the METIS cryostat and a CFRP-based optical bench to optimally cope with alignment flexure. We develop the case for fiber-fed laser sources feeding the integrating sphere for spectral calibration of the LM-Spectrograph of METIS. We detail the activity foreseen for Phase C including the optical tolerances analysis, the eigenfrequency and earthquake analysis and a preparation of the sub-system MAIT work, finishing the paper with a short overview of the WCU future plans.
METIS, the mid-infrared imager and spectrograph for the wavelength range 2.9-14 µm (astronomical L-, M- and N bands), will be equipped with a calibration unit, developed at the University of Cologne, which task is to deliver simulated sources for the test and calibration of the main imaging and spectral functionalities of METIS. Our subsystem, as the full METIS instrument, is currently in the Phase C of the project, which leads to the Final Design Review expected by the end of 2021. In this contribution, we first briefly introduce the general concepts chosen for the Warm Calibration Unit (WCU) and then detail the laboratory work that is undertaken in Cologne to validate most of the concepts presented at the Preliminary Design Review. A core unit of the WCU is the integrating sphere combined with the black body, which is the hub delivering the calibration functionalities. We first report the measured spatial uniformity of the output port of the integrating sphere when fed with the black body source radiation. The measurement made using our uncooled thermal camera, evidences a spatial uniformity below 1% RMS. Longer integration times will further improve the final accuracy on this important parameter. We also take a closer look at the black body source and report on its flux temporal stability, which is found to be better than 1% over a 2h duration. We characterize time windows for different settings of the main WCU light source, which is the black body and stability and repeatability of the detected signal. Through different experiments we investigated the best options to manufacture the aperture mask that will be used to generate artificial point sources.
The use of deployable fibre-bundles plays an increasing role in the design of future Multi-Object-Spectrographs (MOS).
Within a research and development project for "Enabling Technologies for the E-ELT", various miniaturized, fibrebundles
were designed, built and tested for their suitability for a proposed ELT-MOS instrument.
The paper describes the opto-mechanical designs of the bundles and the different manufacture approaches, using glued,
stacked and fused optical fibre bundles. The fibre bundles are characterized for performance, using dedicated testbenches
in the laboratory and at a telescope simulator. Their performance is measured with respect to geometric
accuracy, throughput, FRD behavior and cross-talk between channels.
We here report on recent progress on astronomical optical frequency comb generation at innoFSPEC-Potsdam and
present preliminary test results using the fiber-fed Multi Unit Spectroscopic Explorer (MUSE) spectrograph. The
frequency comb is generated by propagating two free-running lasers at 1554.3 and 1558.9 nm through two dispersionoptimized
nonlinear fibers. The generated comb is centered at 1590 nm and comprises more than one hundred lines with
an optical-signal-to-noise ratio larger than 30 dB. A nonlinear crystal is used to frequency double the whole comb
spectrum, which is efficiently converted into the 800 nm spectral band. We evaluate first the wavelength stability using
an optical spectrum analyzer with 0.02 nm resolution and wavelength grid of 0.01 nm. After confirming the stability
within 0.01 nm, we compare the spectra of the astro-comb and the Ne and Hg calibration lamps: the astro-comb exhibits
a much larger number of lines than lamp calibration sources. A series of preliminary tests using a fiber-fed MUSE
spectrograph are subsequently carried out with the main goal of assessing the equidistancy of the comb lines. Using a
P3d data reduction software we determine the centroid and the width of each comb line (for each of the 400 fibers
feeding the spectrograph): equidistancy is confirmed with an absolute accuracy of 0.4 pm.
VIRUS is the visible, integral-field replicable unit spectrograph for the Hobby-Eberly-Telescope (HET) consisting of 75
integral-field-units that feed 150 spectrographs. The full VIRUS instrument features over 33,000 fibres, each projecting
to 1.5 arcseconds diameter on sky, deployed at the prime focus of the upgraded 10m HET. The assembly and acceptance
testing for all IFUs includes microscopic surface quality inspections, astrometry of fibre positions, relative throughput
measurements, focal-ratio-degradation evaluation, and system acceptance using a VIRUS reference spectrograph to
verify the image quality, spectral transmission, stability, or to detect any stray light issues.
In this paper, we report for the first time the detection of a Cy5-labelled DNA probe immobilised within a 3D hydrogel
matrix formed, inside a hollow core Photonic Crystal Fibre (HC-PCF). We show both the sensitivity of fluorescence
detection inside the HC-PCF using a supercontinuum light source and of the variation of the luminescence intensity with
the concentration DNA probe within the hydrogel. The 3D hydrogel matrix is a network of polymer chains, which is
expected to provide highly sensitive detection and selection of bio-molecules, in comparison with 2D coverage. The
biocompatibility of hydrogel in the HC-PCF suggests numerous applications associated with immobilised DNA probe
detection for point-of-care or remote systems.
The ratio (ζ) of surface tension to viscosity of liquids can be determined using hollow core photonic crystal fibres (HCPCF),
and we show here techniques to determine ζ of glucose levels within fluids, of nano-litre quantities. We
demonstrate an optically integrated micro-capillary viscometer, to determine the concentrations of nano-litre solutions
based on properties of their flow within HC-PCF. The filling of the fibres with liquids within a given range of refractive
index will induce a shift in the photonic band gap of the fibre, allowing guidance of light at wavelengths that were
originally outside the bandgap of the HC-PCF.
In this paper we analyse the optical properties of a 3D hydrogel matrix integrated with a hollow core Photonic
Crystal Fibre (HC-PCF). The overall refractive index was investigated with the aid of a spectroscopic ellipsometer.
Moreover, a supercontinuum source was launched to the filled fibres, for spectrum and near-field analysis. We
observe that when the fibres are filled with hydrogel, a clear shift in wavelength guidance occurs from 1060nm to
approximately 700nm, and that the propagation occurs at the core. We will also discuss possible guidance
mechanisms for such fibre scheme.
In this paper, we show for the first time the integration of a 3D hydrogel matrix within a hollow core Photonic Crystal
Fibre (HC-PCF) and we also show the fluorescence propagation of a Cy5-labelled DNA probe immobilisation within the
hydrogel formed in two different types of HC-PCF. The 3D hydrogel matrix is designed to bind with the amino-groups
of biomolecules, providing higher sensitivity and selectivity than the standard 2D coverage, enabling a greater number of
probe molecules to be available per unit area. The HC-PCFs, on the other hand, are designed to maximise the capture of
fluorescence to improve sensitivity, providing long interaction lengths, being easily integrated with light sources and
detectors, and it can also be implemented in point-of-care or remote systems.