The design and construction of CARMENES has been presented at previous SPIE conferences. It is a next-generation radial-velocity instrument at the 3.5m telescope of the Calar Alto Observatory, which was built by a consortium of eleven Spanish and German institutions. CARMENES consists of two separate échelle spectrographs covering the wavelength range from 0.52 to 1.71μm at a spec-tral resolution of R < 80,000, fed by fibers from the Cassegrain focus of the telescope. CARMENES saw “First Light” on Nov 9, 2015.
During the commissioning and initial operation phases, we established basic performance data such as throughput and spectral resolution. We found that our hollow-cathode lamps are suitable for precise wavelength calibration, but their spectra contain a number of lines of neon or argon that are so bright that the lamps cannot be used in simultaneous exposures with stars. We have therefore adopted a calibration procedure that uses simultaneous star / Fabry Pérot etalon exposures in combination with a cross-calibration between the etalons and hollow-cathode lamps during daytime. With this strategy it has been possible to achieve 1-2 m/s precision in the visible and 5-10 m/s precision in the near-IR; further improvements are expected from ongoing work on temperature control, calibration procedures and data reduction. Comparing the RV precision achieved in different wavelength bands, we find a “sweet spot” between 0.7 and 0.8μm, where deep TiO bands provide rich RV information in mid-M dwarfs. This is in contrast to our pre-survey models, which predicted comparatively better performance in the near-IR around 1μm, and explains in part why our near-IR RVs do not reach the same precision level as those taken with the visible spectrograph.
We are now conducting a large survey of 340 nearby M dwarfs (with an average distance of only 12pc), with the goal of finding terrestrial planets in their habitable zones. We have detected the signatures of several previously known or suspected planets and also discovered several new planets. We find that the radial velocity periodograms of many M dwarfs show several significant peaks. The development of robust methods to distinguish planet signatures from activity-induced radial velocity jitter is therefore among our priorities.
Due to its large wavelength coverage, the CARMENES survey is generating a unique data set for studies of M star atmospheres, rotation, and activity. The spectra cover important diagnostic lines for activity (H alpha, Na I D1 and D2, and the Ca II infrared triplet), as well as FeH lines, from which the magnetic field can be inferred. Correlating the time series of these features with each other, and with wavelength-dependent radial velocities, provides excellent handles for the discrimination between planetary companions and stellar radial velocity jitter. These data are also generating new insight into the physical properties of M dwarf atmospheres, and the impact of activity and flares on the habitability of M star planets.
The CARMENES instrument is a pair of high-resolution (R⪆80,000) spectrographs covering the wavelength range from 0.52 to 1.71 μm, optimized for precise radial velocity measurements. It was installed and commissioned at the 3.5m telescope of the Calar Alto observatory in Southern Spain in 2015. The first large science program of CARMENES is a survey of ~ 300 M dwarfs, which started on Jan 1, 2016. We present an overview of all subsystems of CARMENES (front end, fiber system, visible-light spectrograph, near-infrared spectrograph, calibration units, etalons, facility control, interlock system, instrument control system, data reduction pipeline, data flow, and archive), and give an overview of the assembly, integration, verification, and commissioning phases of the project. We show initial results and discuss further plans for the scientific use of CARMENES.
The 4MOST instrument is a concept for a wide-field, fibre-fed high multiplex spectroscopic instrument facility on the
ESO VISTA telescope designed to perform a massive (initially >25x106 spectra in 5 years) combined all-sky public
survey. The main science drivers are: Gaia follow up of chemo-dynamical structure of the Milky Way, stellar radial
velocities, parameters and abundances, chemical tagging; eROSITA follow up of cosmology with x-ray clusters of
galaxies, X-ray AGN/galaxy evolution to z~5, Galactic X-ray sources and resolving the Galactic edge;
Euclid/LSST/SKA and other survey follow up of Dark Energy, Galaxy evolution and transients. The surveys will be
undertaken simultaneously requiring: highly advanced targeting and scheduling software, also comprehensive data
reduction and analysis tools to produce high-level data products. The instrument will allow simultaneous observations of
~1600 targets at R~5,000 from 390-900nm and ~800 targets at R<18,000 in three channels between ~395-675nm
(channel bandwidth: 45nm blue, 57nm green and 69nm red) over a hexagonal field of view of ~ 4.1 degrees. The initial
5-year 4MOST survey is currently expect to start in 2020. We provide and overview of the 4MOST systems: optomechanical,
control, data management and operations concepts; and initial performance estimates.
The 4MOST consortium is currently halfway through a Conceptual Design study for ESO with the aim to develop a wide-field ( < 3 square degree, goal < 5 square degree), high-multiplex ( < 1500 fibres, goal 3000 fibres) spectroscopic survey facility for an ESO 4m-class telescope (VISTA). 4MOST will run permanently on the telescope to perform a 5 year public survey yielding more than 20 million spectra at resolution R∼5000 (λ=390–1000 nm) and more than 2 million spectra at R~20,000 (395–456.5 nm and 587–673 nm). The 4MOST design is especially intended to complement three key all-sky, space-based observatories of prime European interest: Gaia, eROSITA and Euclid. Initial design and performance estimates for the wide-field corrector concepts are presented. Two fibre positioner concepts are being considered for 4MOST. The first one is a Phi-Theta system similar to ones used on existing and planned facilities. The second one is a new R-Theta concept with large patrol area. Both positioner concepts effectively address the issues of fibre focus and pupil pointing. The 4MOST spectrographs are fixed configuration two-arm spectrographs, with dedicated spectrographs for the high- and low-resolution fibres. A full facility simulator is being developed to guide trade-off decisions regarding the optimal field-of-view, number of fibres needed, and the relative fraction of high-to-low resolution fibres. The simulator takes mock catalogues with template spectra from Design Reference Surveys as starting point, calculates the output spectra based on a throughput simulator, assigns targets to fibres based on the capabilities of the fibre positioner designs, and calculates the required survey time by tiling the fields on the sky. The 4MOST consortium aims to deliver the full 4MOST facility by the end of 2018 and start delivering high-level data products for both consortium and ESO community targets a year later with yearly increments.
There is a limited variety of pore shapes that can be attained by electrochemical etching itself. We show that these
limitations can be overcome and new pore geometries can be realized by additional post-etching treatment of
macroporous silicon. Repeated oxidation and subsequent oxide-removal steps are used to correct the initially faceted
pore cross-section and to obtain cylindrical pores. We demonstrate that the anisotropy of oxidation process is just
opposite to the anisotropy exhibited by the electrochemical etching and accounts for the observed evolution of pore
shape from a rounded square towards circular one. On the other hand, alkaline post-etching treatment is used to fabricate
pores with square cross-section. Careful choice of concentration, alcohol additives and temperature of alkaline solution
allows for certain crystallographic directions to be preferentially etched. In this way, pores with square, eight-sided
(octagonal) or rotated square shapes can be attained. When applied on 2D macropore arrays with modulated pores, such
post-etching treatment enables the realization of truly 3D structures with very complex geometries.
This work describes the infiltration of a polymeric solution into porous Si structures towards the fabrication of
tunable photonic crystals (PC) and microcavities for photonics applications. The tunability is achieved by infiltrating the
porous silicon based PCs by active organic materials, such as an emissive and nonlinear polymer called 2-methoxy-5-(2-
ethylhexyloxy)-p-phenylenevinylene (namely MEH-PPV). This preliminary work shows the infiltration of this polymeric
solution into PC based on macroporous Si structure as well as in microcavities based on multiple layers of microporous
Si. The solidification of the polymer was obtained by the evaporation of the solvent. Various techniques of infiltration
were studied to obtain an optimized filling of the pores. The infiltration was then characterized using photoluminescence
measurements. Finally, we will report on the study of third harmonic generation (THG) in samples of porous silicon
microcavity infiltrated with MEHPPV. The k-domain THG spectroscopy was applied and an increase of the THG
intensity up to an order of magnitude was achieved for the filled microcavity.
In recent years it became clear the relevance of photonic crystals when considering a nonlinear interaction. It has been shown in many occasions that the structuring of the material results in a clear enhancement of the nonlinear interaction. However, not too many structuring technologies can be applied successfully to materials that exhibit very good physical properties for the nonlinear generation of light. One of these is KTiOPO4 (KTP), an inorganic material with high nonlinearity, large electrooptical coefficients, and very good transparency in the near infrared and visible range. In this paper, we propose a novel technique for growing two-dimensional KTP-air photonic crystals by liquid phase epitaxy employing a two-dimensional ordered macroporous Si matrix as a template.
We study the photonic band gap formation in 2D photonic crystals comprising rods covered with a thin interfacial layer. The dielectric constant of the interfacial layer is different from that of the rods and background material. The rod together with the surrounding interfacial layer can therefore be treated as a single rod having a core and cladding regions. We study how the thickness and the dielectric constant of the cladding material affect the properties of photonic gaps in 2D photonic lattices. Specifically, we consider triangular and honeycomb lattices consisting of air rods drilled in silicon matrix and silicon rods in air, respectively. Photonic band simulations of such structures are presented performed using both finite-difference time-domain and plane-wave expansion methods. We show that the physical properties of the cladding layer strongly influence the photonic gap parameters. In particular, the existence of dielectric cladding reduces the absolute PBG in case of air rods drilled in a dielectric host, but may lead to larger absolute gaps in case of dielectric rods embedded in air. We also discuss the practical technological feasibility of these structures and their experimental realization.
Macroporous silicon structures have been fabricated by electrochemical etching. Such fabrication process is known to result in the presence of a thin microporous Si layer at the walls of the macropores and at the surface. Photoluminescence measurements conducted in plan-view and cross-section exhibit a wide emission peak around 650nm which can be attributed to the microporous Si. The combination of a photonic crystal and a light emitter in one structure represents a potential for applications that has not been studied previously. This preliminary study shows the influence of the main fabrication parameters, namely the current density and the etchant solution, on the emission properties of the microporous Si layer.
A part of the results obtained during the winter experimental campaign 'LIRADEX'98' are presented. A vertically sounding aerosol lidar and a thermal infrared radiometer were used for joint investigation of low clouds. Both devices were placed at height of about 12 m above the ground and about 25 m apart. Data about the atmospheric parameters were obtained by parallel standard aerological observation. The experimental campaign extended two weeks during November and December, 1998. The data discussed in the presented paper are obtained on December 2, 1998.
The lidar technique used provides simultaneous recording of parallel and cross polarized components of the returned signal at different viewing angles of the receiving optics. The experimental data consist of time series of both polarized components recorded from different distances along the sounding path within the cloud. The auto-correlation functions of both polarization components are calculated using the time series of the lidar signal obtained at different distances. The auto-correlation functions of the parallel component of the lidar signal show two zones within the cloud, where the aerosol backscattering coefficient has close values. The auto- correlation functions of the cross component of the signal reveals the existence of a similar zone, which determines the area which the multiple scattering develops in the same manner. The cross-correlation functions of the parallel and cross components of the polarized signals confirm our suggestions as they show a time delay of approximately 150 ns.
Lidars and widely used for investigations of dense atmospheric objects (fogs, clouds, smoke trails) both for the needs of meteorology and ecology. The polarization studies give additional information about the optical and microphysical properties of the observed objects and phenomena. Two main factors determine the polarization state of the backscattered laser radiation: the shape and size of the scattering particles and the multiple scattering effects. The present work aims at determining the prevailing contribution of one of the factors in different atmospheric situations. Radiative fog and Sc clouds have been investigated by means of polarization aerosol lidar. The multiple scattering contribution was studied by varying the viewing angle of the lidar. On the basis of the lidar data an empirical relation is proposed describing the dependence of the lidar signal depolarization on the viewing angle. On the basis of the particular depolarization coefficient values obtained conclusion is drawn up about the phase composition of the cloud formations.
The preliminary results obtained during the experimental campaign `LIRADEX'98' are presented. A vertically sounding aerosol lidar and an infrared optical radiometer were used to investigate low clouds. Both devices were placed at height of about 12 m above the ground and about 25 m apart. Data about the atmospheric parameters were obtained by parallel standard aerological observation. The experimental campaign extended two weeks--from 06.05.1998 to 19.05.1998. The data presented in the paper are from 08.05.1998.
In the paper some results of polarization investigations of various objects and phenomena in the atmospheric planetary boundary layer performed by a ground-based lidar are presented. An attempt is made the frontal zone passing to be followed in more detail. The dynamics of the cloud system formation is observed. Differences between the optical properties of the aerosol near the clouds base and top are established; through the depolarization coefficient changes within the clouds the phase composition of the latter is determined.
In the present work some results of polarization measurements in the planetary boundary layer are reported. The observations described were performed by a ground-based lidar over the region of the Sofia city (where various industrial enterprises exist along with a heavy transport and aerial communications). The data obtained when sounding in different meteorological situations (`clear' atmosphere, rain, fog, snowfall) are considered. Certain differences are established in the depolarization properties of `clear' atmosphere in dependence of the meteorological condition. The developments of fog and snowfall are traced; the effects of the underlying surface are sought when sounding in fog; various types of situations during a snowfall are pointed as well. An attempt is made to follow the development of the processes which proceed during an interaction between air masses with different properties (e.g. a front advection); as a result the formation of the cloud system over the region is traced. Definite differences between the microphysical properties of the aerosol near the clouds (Fmb, Ns) base and top are established as well.