48 research outputs found
A Demonstration of Wavefront Sensing and Mirror Phasing from the Image Domain
In astronomy and microscopy, distortions in the wavefront affect the dynamic
range of a high contrast imaging system. These aberrations are either imposed
by a turbulent medium such as the atmosphere, by static or thermal aberrations
in the optical path, or by imperfectly phased subapertures in a segmented
mirror. Active and adaptive optics (AO), consisting of a wavefront sensor and a
deformable mirror, are employed to address this problem. Nevertheless, the
non-common-path between the wavefront sensor and the science camera leads to
persistent quasi-static speckles that are difficult to calibrate and which
impose a floor on the image contrast. In this paper we present the first
experimental demonstration of a novel wavefront sensor requiring only a minor
asymmetric obscuration of the pupil, using the science camera itself to detect
high order wavefront errors from the speckle pattern produced. We apply this to
correct errors imposed on a deformable microelectromechanical (MEMS) segmented
mirror in a closed loop, restoring a high quality point spread function (PSF)
and residual wavefront errors of order nm using 1600 nm light, from a
starting point of nm in piston and mrad in tip-tilt. We
recommend this as a method for measuring the non-common-path error in
AO-equipped ground based telescopes, as well as as an approach to phasing
difficult segmented mirrors such as on the \emph{James Webb Space Telescope}
primary and as a future direction for extreme adaptive optics.Comment: 9 pages, 6 figure
Fabrication tolerant chalcogenide mid-infrared multimode interference coupler design with application for Bracewell nulling interferometry
Understanding exoplanet formation and finding potentially habitable
exoplanets is vital to an enhanced understanding of the universe. The use of
nulling interferometry to strongly attenuate the central starlight provides the
opportunity to see objects closer to the star than ever before. Given that
exoplanets are usually warm, the 4 microns Mid-Infrared region is advantageous
for such observations. The key performance parameters for a nulling
interferometer are the extinction ratio it can attain and how well that is
maintained across the operational bandwidth. Both parameters depend on the
design and fabrication accuracy of the subcomponents and their wavelength
dependence. Via detailed simulation it is shown in this paper that a planar
chalcogenide photonic chip, consisting of three highly fabrication tolerant
multimode interference couplers, can exceed an extinction ratio of 60 dB in
double nulling operation and up to 40 dB for a single nulling operation across
a wavelength window of 3.9 to 4.2 microns. This provides a beam combiner with
sufficient performance, in theory, to image exoplanets.This research was supported by the Australian Research Council (ARC) Centre of Excellence
for Ultrahigh bandwidth Devices for Optic Systems (CUDOS) project CE110001018
Diffraction-limited polarimetric imaging of protoplanetary disks and mass-loss shells with VAMPIRES
Both the birth and death of a stellar system are areas of key scientific importance. Whether it's understanding the process of planetary formation in a star's early years, or uncovering the cause of the enormous mass-loss that takes place during a star's dying moments, a key to scientific understanding lies in the inner few AU of the circumstellar environment. Corresponding to scales of 10s of milli-arcseconds, these observations pose a huge technical challenge due to the high angular-resolutions and contrasts required. A major stumbling block is the problem of the Earth's own atmospheric turbulence. The other difficulty is that precise calibration is required to combat the extremely high contrast ratios and high resolutions faced. By taking advantage of the fact that starlight scattered by dust in the circumstellar region is polarized, differential polarimetry can help achieve this calibration. Spectral features can also be utilized
High-performance 3D waveguide architecture for astronomical pupil-remapping interferometry
The detection and characterisation of extra-solar planets is a major theme
driving modern astronomy, with the vast majority of such measurements being
achieved by Doppler radial-velocity and transit observations. Another technique
-- direct imaging -- can access a parameter space that complements these
methods, and paves the way for future technologies capable of detailed
characterization of exoplanetary atmospheres and surfaces. However achieving
the required levels of performance with direct imaging, particularly from
ground-based telescopes which must contend with the Earth's turbulent
atmosphere, requires considerable sophistication in the instrument and
detection strategy. Here we demonstrate a new generation of photonic
pupil-remapping devices which build upon the interferometric framework
developed for the {\it Dragonfly} instrument: a high contrast waveguide-based
device which recovers robust complex visibility observables. New generation
Dragonfly devices overcome problems caused by interference from unguided light
and low throughput, promising unprecedented on-sky performance. Closure phase
measurement scatter of only has been achieved, with waveguide
throughputs of . This translates to a maximum contrast-ratio
sensitivity (between the host star and its orbiting planet) at
(1 detection) of (when a conventional
adaptive-optics (AO) system is used) or (for typical
`extreme-AO' performance), improving even further when random error is
minimised by averaging over multiple exposures. This is an order of magnitude
beyond conventional pupil-segmenting interferometry techniques (such as
aperture masking), allowing a previously inaccessible part of the star to
planet contrast-separation parameter space to be explored
Diffraction-limited polarimetric imaging of protoplanetary disks and mass-loss shells with VAMPIRES
Both the birth and death of a stellar system are areas of key scientific importance. Whether it's understanding the process of planetary formation in a star's early years, or uncovering the cause of the enormous mass-loss that takes place during a star's dying moments, a key to scientific understanding lies in the inner few AU of the circumstellar environment. Corresponding to scales of 10s of milli-arcseconds, these observations pose a huge technical challenge due to the high angular-resolutions and contrasts required. A major stumbling block is the problem of the Earth's own atmospheric turbulence. The other difficulty is that precise calibration is required to combat the extremely high contrast ratios and high resolutions faced. By taking advantage of the fact that starlight scattered by dust in the circumstellar region is polarized, differential polarimetry can help achieve this calibration. Spectral features can also be utilized
High-contrast detection of exoplanets with a kernel-nuller at the VLTI
Context: The conventional approach to direct imaging has been the use of a
single aperture coronagraph with wavefront correction via extreme adaptive
optics. Such systems are limited to observing beyond an inner working (IWA) of
a few . Nulling interferometry with two or more apertures
will enable detections of companions at separations at and beyond the formal
diffraction limit.
Aims: This paper evaluates the astrophysical potential of a kernel-nuller as
the prime high-contrast imaging mode of the Very Large Telescope Interferometer
(VLTI).
Methods: By taking into account baseline projection effects which are induced
by Earth rotation, we introduce some diversity in the response of the nuller as
a function of time. This response is depicted by transmission maps. We also
determine whether we can extract the astrometric parameters of a companion from
the kernel outputs, which are the primary intended observable quantities of the
kernel-nuller. This then leads us to comment on the characteristics of a
possible observing program for the discovery of exoplanets.
Results: We present transmission maps for both the raw nuller outputs and
their subsequent kernel outputs. To further examine the properties of the
kernel-nuller, we introduce maps of the absolute value of the kernel output. We
also identify 38 targets for the direct detection of exoplanets with a
kernel-nuller at the focus of the VLTI.
Conclusions: With continued upgrades of the VLTI infrastructure that will
reduce fringe tracking residuals, a kernel-nuller would enable the detection of
young giant exoplanets at separations < 10 AU, where radial velocity and
transit methods are more sensitive.Comment: 13 pages, 12 figure
Developing arrayed waveguide grating spectrographs for multi-object astronomical spectroscopy
With the aim of utilizing arrayed waveguide gratings for multi-object
spectroscopy in the field of astronomy, we outline several ways in which
standard telecommunications grade chips should be modified. In particular, by
removing the parabolic-horn taper or multimode interference coupler, and
injecting with an optical fiber directly, the resolving power was increased
threefold from 2400 \pm 200 (spectral resolution of 0.63 \pm 0.2 nm) to 7000
\pm 700 (0.22 \pm 0.02 nm) while attaining a throughput of 77 \pm 5%. More
importantly, the removal of the taper enabled simultaneous off-axis injection
from multiple fibers, significantly increasing the number of spectra that can
be obtained at once (i.e. the observing efficiency). Here we report that ~ 12
fibers can be injected simultaneously within the free spectral range of our
device, with a 20% reduction in resolving power for fibers placed at 0.8 mm off
centre.Comment: 11 Pages, 5 Figure
Flattening laser frequency comb spectra with a high dynamic range, broadband spectral shaper on-a-chip
Spectral shaping is critical to many fields of science. In astronomy for
example, the detection of exoplanets via the Doppler effect hinges on the
ability to calibrate a high resolution spectrograph. Laser frequency combs can
be used for this, but the wildly varying intensity across the spectrum can make
it impossible to optimally utilize the entire comb, leading to a reduced
overall precision of calibration. To circumvent this, astronomical applications
of laser frequency combs rely on a bulk optic setup which can flatten the
output spectrum before sending it to the spectrograph. Such flatteners require
complex and expensive optical elements like spatial light modulators and have
non-negligible bench top footprints. Here we present an alternative in the form
of an all-photonic spectral shaper that can be used to flatten the spectrum of
a laser frequency comb. The device consists of a circuit etched into a silicon
nitride wafer that supports an arrayed-waveguide grating to disperse the light
over hundreds of nanometers in wavelength, followed by Mach-Zehnder
interferometers to control the amplitude of each channel, thermo-optic phase
modulators to phase the channels and a second arrayed-waveguide grating to
recombine the spectrum. The demonstrator device operates from 1400 to 1800 nm
(covering the astronomical H band), with twenty 20 nm wide channels. The device
allows for nearly 40 dBs of dynamic modulation of the spectrum via the
Mach-Zehnders , which is greater than that offered by most spatial light
modulators. With a superluminescent diode, we reduced the static spectral
variation to ~3 dB, limited by the properties of the components used in the
circuit and on a laser frequency comb we managed to reduce the modulation to 5
dBs, sufficient for astronomical applications.Comment: 15 pages, 10 figures. arXiv admin note: substantial text overlap with
arXiv:2209.0945