29 research outputs found
Using the generalised-optical differentiation wavefront sensor for laser guide star wavefront sensing
Laser guide stars (LGS) are used in many adaptive optics systems to extend sky coverage. The most common wavefront sensor used in combination with a LGS is a Shack-Hartmann wavefront sensor (SHWFS). The ShackHartmann has a major disadvantage for extended source wavefront sensing because it directly samples the image. In this proceeding we propose to use the generalized-Optical Differentation Wavefront Sensor (g-ODWFS) a wavefront sensor for wavefront sensing of LGS. The g-ODWFS uses only 4 pixels per sub-aperture, has little to no aliasing noise and therefore no spurious low-order errors and has no need for centroid gain calibrations. In this proceeding we show the results of simulations that compare the g-ODWFS with the SHWFS
Laboratory demonstration of the triple-grating vector vortex coronagraph
The future Habitable Worlds Observatory aims to characterize the atmospheres
of rocky exoplanets around solar-type stars. The vector vortex coronagraph
(VVC) is a main candidate to reach the required contrast of .
However, the VVC requires polarization filtering and every observing band
requires a different VVC. The triple-grating vector vortex coronagraph (tgVVC)
aims to mitigate these limitations by combining multiple gratings that minimize
the polarization leakage over a large spectral bandwidth. In this paper, we
present laboratory results of a tgVVC prototype using the In-Air Coronagraphic
Testbed (IACT) facility at NASA's Jet Propulsion Laboratory and the Space
Coronagraph Optical Bench (SCoOB) at the University of Arizona Space
Astrophysics Lab (UASAL). We study the coronagraphic performance with
polarization filtering at 633 nm and reach a similar average contrast of between 3-18 at the IACT, and
between 3-14 at SCoOB. We explore the limitations of the tgVVC by
comparing the testbed results. We report on other manufacturing errors and ways
to mitigate their impact.Comment: 9 pages, 5 figures, SPIE Optics + Photonics - Techniques and
Instrumentation for Detection of Exoplanets X
Search for Rayleigh scattering in the atmosphere of GJ1214b
We investigate the atmosphere of GJ1214b, a transiting super-Earth planet
with a low mean density, by measuring its transit depth as a function of
wavelength in the blue optical portion of the spectrum. It is thought that this
planet is either a mini-Neptune, consisting of a rocky core with a thick,
hydrogen-rich atmosphere, or a planet with a composition dominated by water.
Most observations favor a water-dominated atmosphere with a small scale-height,
however, some observations indicate that GJ1214b could have an extended
atmosphere with a cloud layer muting the molecular features. In an atmosphere
with a large scale-height, Rayleigh scattering at blue wavelengths is likely to
cause a measurable increase in the apparent size of the planet towards the
blue. We observed the transit of GJ1214b in the B-band with the FOcal Reducing
Spectrograph (FORS) at the Very Large Telescope (VLT) and in the g-band with
both ACAM on the William Hershel Telescope (WHT) and the Wide Field Camera
(WFC) at the Isaac Newton Telescope (INT). We find a planet-to-star radius
ratio in the B-band of 0.1162+/-0.0017, and in the g-band 0.1180+/-0.0009 and
0.1174+/-0.0017 for the WHT & INT observations respectively. These optical data
do not show significant deviations from previous measurements at longer
wavelengths. In fact, a flat transmission spectrum across all wavelengths best
describes the combined observations. When atmospheric models are considered a
small scale-height water-dominated model fits the data best.Comment: Accepted for publication in Ap
Estimation of polarization aberrations and their effect on the coronagraphic performance for future space telescopes
A major goal of proposed future space observatories, such as the Habitable
World Observatory, is to directly image and characterize Earth-like planets
around Sun-like stars to search for habitability signatures requiring the
starlight suppression (contrast) of 1e-10. One of the significant aspects
affecting this contrast is the polarization aberrations generated from the
reflection from mirror surfaces. The polarization aberrations are the
phase-dependent amplitude and phase patterns originating from the Fresnel
reflections of the mirror surfaces. These aberrations depend on the angle of
incidence and coating parameters of the surface. This paper simulates the
polarization aberrations for an on-axis and off-axis TMA telescope of a 6.5 m
monolithic primary mirror. We analyze the polarization aberrations and their
effect on the coronagraphic performance for eight different recipes of mirror
coatings for Astronomical filter bands g-I: three single-layer metal coatings
and five recipes of protective coatings. First, the Jones pupils are estimated
for each coating and filter band using the polarization ray tracing in Zemax.
Then, we propagate these Jones pupils through a Vector Vortex Coronagraph and
Perfect Coronagraphs using hcipy, a physical optics-based simulation framework.
The analysis shows that the two main polarization aberrations generated from
the four mirrors are the retardance-defocus and retardance-tilt. The
simulations also show that the coating plays a significant role in determining
the strength of the aberrations. The bare/oxi-aluminum and Al+18nm LiF coating
outperforms all the other coatings by one order of magnitude.Comment: 13 pages, 11 figures, SPIE Optics+Photonics 2023 proceeding, Paper
no: 12680-2
Using the Gerchberg-Saxton algorithm to reconstruct non-modulated pyramid wavefront sensor measurements
Adaptive optics (AO) is a technique to improve the resolution of ground-based
telescopes by correcting, in real-time, optical aberrations due to atmospheric
turbulence and the telescope itself. With the rise of Giant Segmented Mirror
Telescopes (GSMT), AO is needed more than ever to reach the full potential of
these future observatories. One of the main performance drivers of an AO system
is the wavefront sensing operation, consisting of measuring the shape of the
above mentioned optical aberrations. Aims. The non-modulated pyramid wavefront
sensor (nPWFS) is a wavefront sensor with high sensitivity, allowing the limits
of AO systems to be pushed. The high sensitivity comes at the expense of its
dynamic range, which makes it a highly non-linear sensor. We propose here a
novel way to invert nPWFS signals by using the principle of reciprocity of
light propagation and the Gerchberg-Saxton (GS) algorithm. We test the
performance of this reconstructor in two steps: the technique is first
implemented in simulations, where some of its basic properties are studied.
Then, the GS reconstructor is tested on the Santa Cruz Extreme Adaptive optics
Laboratory (SEAL) testbed located at the University of California Santa Cruz.
This new way to invert the nPWFS measurements allows us to drastically increase
the dynamic range of the reconstruction for the nPWFS, pushing the dynamics
close to a modulated PWFS. The reconstructor is an iterative algorithm
requiring heavy computational burden, which could be an issue for real-time
purposes in its current implementation. However, this new reconstructor could
still be helpful in the case of many wavefront control operations. This
reconstruction technique has also been successfully tested on the Santa Cruz
Extreme AO Laboratory (SEAL) bench where it is now used as the standard way to
invert nPWFS signal
Polarization aberrations in next-generation giant segmented mirror telescopes (GSMTs) I. Effect on the coronagraphic performance
Next-generation large segmented mirror telescopes are expected to perform
direct imaging and characterization of Earth-like rocky planets, which requires
contrast limits of to at wavelengths from I to J band. One
critical aspect affecting the raw on-sky contrast are polarization aberrations
arising from the reflection from the telescope's mirror surfaces and instrument
optics. We simulate the polarization aberrations and estimate their effect on
the achievable contrast for three next-generation ground-based large segmented
mirror telescopes. We performed ray-tracing in Zemax and computed the
polarization aberrations and Jones pupil maps using the polarization
ray-tracing algorithm. The impact of these aberrations on the contrast is
estimated by propagating the Jones pupil maps through a set of idealized
coronagraphs using hcipy, a physical optics-based simulation framework. The
optical modeling of the giant segmented mirror telescopes (GSMTs) shows that
polarization aberrations create significant leakage through a coronagraphic
system. The dominant aberration is retardance defocus, which originates from
the steep angles on the primary and secondary mirrors. The retardance defocus
limits the contrast to to at 1 at visible
wavelengths, and to at infrared wavelengths. The
simulations also show that the coating plays a major role in determining the
strength of the aberrations. Polarization aberrations will need to be
considered during the design of high-contrast imaging instruments for the next
generation of extremely large telescopes. This can be achieved either through
compensation optics, robust coronagraphs, specialized coatings, calibration,
and data analysis approaches or by incorporating polarimetry with high-contrast
imaging to measure these effects.Comment: 18 pages, 12 figures, Accepted in Astronomy & Astrophysics manuscript
no. aa45651-2
Multi-core fibre-fed integral field spectrograph (MCIFU) IV:The fiber link
The Multi-Core Integral-Field Unit (MCIFU) is a diffraction-limited near-infrared integral-field spectrograph designed to detect and characterise exoplanets and disks in combination with extreme adaptive optics (xAO) instruments. It has been developed by an extended consortium as an experimental path finder for medium resolution spectroscopic upgrades for xAO systems. To allow it to achieve its goals we manufactured a fibre link system composed of a custom integrated fiber, with 3D printed microlenses and an ultrafast laser inscribed reformatter. Here we detail the specific requirements of the fibre link, from its design parameters, through its manufacture the laboratory performance and discuss upgrades for the future. © 2020 SPIE.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
L-band Integral Field Spectroscopy of the HR 8799 Planetary System
Understanding the physical processes sculpting the appearance of young
gas-giant planets is complicated by degeneracies confounding effective
temperature, surface gravity, cloudiness, and chemistry. To enable more
detailed studies, spectroscopic observations covering a wide range of
wavelengths is required. Here we present the first L-band spectroscopic
observations of HR 8799 d and e and the first low-resolution wide bandwidth
L-band spectroscopic measurements of HR 8799 c. These measurements were
facilitated by an upgraded LMIRCam/ALES instrument at the LBT, together with a
new apodizing phase plate coronagraph. Our data are generally consistent with
previous photometric observations covering similar wavelengths, yet there
exists some tension with narrowband photometry for HR 8799 c. With the addition
of our spectra, each of the three innermost observed planets in the HR 8799
system have had their spectral energy distributions measured with integral
field spectroscopy covering to . We combine these
spectra with measurements from the literature and fit synthetic model
atmospheres. We demonstrate that the bolometric luminosity of the planets is
not sensitive to the choice of model atmosphere used to interpolate between
measurements and extrapolate beyond them. Combining luminosity with age and
mass constraints, we show that the predictions of evolutionary models are
narrowly peaked for effective temperature, surface gravity, and planetary
radius. By holding these parameters at their predicted values, we show that
more flexible cloud models can provide good fits to the data while being
consistent with the expectations of evolutionary models.Comment: 19 pages, 11 figures, accepted for publication in The Astronomical
Journal; added reference, updated figure 6 and table
Improved companion mass limits for Sirius A with thermal infrared coronagraphy using a vector-apodizing phase plate and time-domain starlight-subtraction techniques
We use observations with the infrared-optimized MagAO system and Clio camera
in 3.9 m light to place stringent mass constraints on possible undetected
companions to Sirius A. We suppress the light from Sirius A by imaging it
through a grating vector-apodizing phase plate coronagraph with 180-degree dark
region (gvAPP-180). To remove residual starlight in post-processing, we apply a
time-domain principal-components-analysis-based algorithm we call PCA-Temporal
(PCAT), which uses eigen-time-series rather than eigen-images to subtract
starlight. By casting the problem in terms of eigen-time-series, we reduce the
computational cost of post-processing the data, enabling the use of the fully
sampled dataset for improved contrast at small separations. We also discuss the
impact of retaining fine temporal sampling of the data on final contrast
limits. We achieve post-processed contrast limits of to
outside of 0.75 arcsec which correspond to planet masses
of 2.6 to 8.0 . These are combined with values from the recent literature
of high-contrast imaging observations of Sirius to synthesize an overall
completeness fraction as a function of mass and separation. After synthesizing
these recent studies and our results, the final completeness analysis rules out
99% of planets from 2.5-7 AU.Comment: 19 pages, 22 figures, accepted to A