50 research outputs found
Stabilising a nulling interferometer using optical path difference dithering
Context. Nulling interferometry has been suggested as the underlying
principle for the Darwin and TPF-I exoplanet research missions. Aims. There are
constraints both on the mean value of the nulling ratio, and on its stability.
Instrument instability noise is most detrimental to the stability of the
nulling performance. Methods. We applied a modified version of the classical
dithering technique to the optical path difference in the scientific beam.
Results. Using only this method, we repeatedly stabilised the dark fringe for
several hours. This method alone sufficed to remove the 1/ f component of the
noise in our setup for periods of 10 minutes, typically. These results indicate
that performance stability may be maintained throughout the long-duration data
acquisitions typical of exoplanet spectroscopy. Conclusions. We suggest that
further study of possible stabilisation strategies should be an integral part
of Darwin/TPF-I research and developmen
Broadband near-infrared astronomical spectrometer calibration and on-sky validation with an electro-optic laser frequency comb
The quest for extrasolar planets and their characterisation as well as
studies of fundamental physics on cosmological scales rely on capabilities of
high-resolution astronomical spectroscopy. A central requirement is a precise
wavelength calibration of astronomical spectrographs allowing for extraction of
subtle wavelength shifts from the spectra of stars and quasars. Here, we
present an all-fibre, 400 nm wide near-infrared frequency comb based on
electro-optic modulation with 14.5 GHz comb line spacing. Tests on the
high-resolution, near-infrared spectrometer GIANO-B show a photon-noise limited
calibration precision of <10 cm/s as required for Earth-like planet detection.
Moreover, the presented comb provides detailed insight into particularities of
the spectrograph such as detector inhomogeneities and differential spectrograph
drifts. The system is validated in on-sky observations of a radial velocity
standard star (HD221354) and telluric atmospheric absorption features. The
advantages of the system include simplicity, robustness and turn-key operation,
features that are valuable at the observation sites
KalAO the swift adaptive optics imager on the 1.2m Euler Swiss telescope in La Silla, Chile
KalAO is a natural guide star adaptive optics (AO) imager to be installed on the second Nasmyth focus of the 1.2m Euler Swiss telescope in La Silla, Chile. The initial design of the system is inspired on RoboAO with modifications in order to operate in natural guide star (NGS) mode. KalAO was built to search for binarity in planet hosting stars by following-up candidates primarily from the TESS satellite survey. The optical design is optimised for the 450-900 nm wavelength range and is fitted with SDSS g,r,i,z filters. The system is designed for wavefront control down to I-magnitude 11 stars in order to probe the same parameter space as radial velocity instruments such as HARPS and NIRPS. The principal components of the system are an 11x11 10.9 cm sub-apertures Electron Multiplying CCD (EMCCD) Shack-Hartmann wavefront sensor, a 140 actuators Microelectromechanical systems (MEMS) deformable mirror, a fast tip/tilt mirror, and a graphics processing unit (GPU) powered glycol cooled real-time computer. It is designed to run at up to 1.8kHz in order to detect companions as close as the 150mas visible-light diffraction limit. The real-time adaptive optics control is using the CACAO software running on GPUs. The instrument is planned for commissioning early 2021 in Chile if the covid restrictions are lifted
Tests of achromatic phase shifters performed on the SYNAPSE test bench: a progress report
The achromatic phase shifter (APS) is a component of the Bracewell nulling
interferometer studied in preparation for future space missions (viz.
Darwin/TPF-I) focusing on spectroscopic study of Earth-like exo-planets.
Several possible designs of such an optical subsystem exist. Four approaches
were selected for further study. Thales Alenia Space developed a dielectric
prism APS. A focus crossing APS prototype was developed by the OCA, Nice,
France. A field reversal APS prototype was prepared by the MPIA in Heidelberg,
Germany. Centre Spatial de Li\`ege develops a concept based on Fresnel's
rhombs. This paper presents a progress report on the current work aiming at
evaluating these prototypes on the SYNAPSE test bench at the Institut
d'Astrophysique Spatiale in Orsay, France
RISTRETTO: a pathfinder instrument for exoplanet atmosphere characterization
We introduce the RISTRETTO instrument for ESO VLT, an evolution from the
original idea of connecting the SPHERE high-contrast facility to the ESPRESSO
spectrograph (Lovis et al 2017). RISTRETTO is an independent, AO-fed
spectrograph proposed as a visitor instrument, with the goal of detecting
nearby exoplanets in reflected light for the first time. RISTRETTO aims at
characterizing the atmospheres of Proxima b and several other exoplanets using
the technique of high-contrast, high-resolution spectroscopy. The instrument is
composed of two parts: a front-end to be installed on VLT UT4 providing a
two-stage adaptive optics system using the AOF facility with coronagraphic
capability and a 7-fiber IFU, and a diffraction-limited R=135,000 spectrograph
in the 620-840 nm range. We present the requirements and the preliminary design
of the instrument
ELT -HIRES the High Resolution Spectrograph for the ELT:Fabry-Pérots for use as calibration sources
Opto-thermo-mechanical numerical simulations of 3 different concepts of infrared achromatic phase shifters
The Darwin/TPF mission aims at detecting directly extra solar planets. It is based on the nulling interferometry, concept proposed by Bracewell in 1978, and developed since 1995 in several European and American laboratories. One of the key optical devices for this technique is the achromatic phase shifter (APS). This optical component is designed to produce a π phase shift over the whole Darwin spectral range (i.e. 6-18 μm), and will be experimentally tested on the NULLTIMATE consortium nulling test bench (Labèque et al). Three different concepts of APS are being simulated: dispersive plates focus crossing and field reversal. In this paper, we show how thermal, mechanical and optical models are merged into a single robust model, allowing a global numerical simulation of the optical component performances. We show how these simulations help us to optimizing the design and present results of the numerical model
Darwin -— an experimental astronomy mission to search for extrasolar planets
As a response to ESA call for mission concepts for its Cosmic Vision 2015–2025 plan, we propose a mission called Darwin. Its primary goal is the study of terrestrial extrasolar planets and the search for life on them. In this paper, we describe different characteristics of the instrument
Ultraviolet astronomical spectrograph calibration with laser frequency combs from nanophotonic waveguides
Astronomical precision spectroscopy underpins searches for life beyond Earth,
direct observation of the expanding Universe and constraining the potential
variability of physical constants across cosmological scales. Laser frequency
combs can provide the critically required accurate and precise calibration to
the astronomical spectrographs. For cosmological studies, extending the
calibration with such astrocombs to the ultraviolet spectral range is highly
desirable, however, strong material dispersion and large spectral separation
from the established infrared laser oscillators have made this exceedingly
challenging. Here, we demonstrate for the first time astronomical spectrograph
calibrations with an astrocomb in the ultraviolet spectral range below 400 nm.
This is accomplished via chip-integrated highly nonlinear photonics in
periodically-poled, nano-fabricated lithium niobate waveguides in conjunction
with a robust infrared electro-optic comb generator, as well as a
chip-integrated microresonator comb. These results demonstrate a viable route
towards astronomical precision spectroscopy in the ultraviolet and may
contribute to unlocking the full potential of next generation ground- and
future space-based astronomical instruments