16 research outputs found
Impact of time-variant turbulence behavior on prediction for adaptive optics systems
For high contrast imaging systems, the time delay is one of the major
limiting factors for the performance of the extreme adaptive optics (AO)
sub-system and, in turn, the final contrast. The time delay is due to the
finite time needed to measure the incoming disturbance and then apply the
correction. By predicting the behavior of the atmospheric disturbance over the
time delay we can in principle achieve a better AO performance. Atmospheric
turbulence parameters which determine the wavefront phase fluctuations have
time-varying behavior. We present a stochastic model for wind speed and model
time-variant atmospheric turbulence effects using varying wind speed. We test a
low-order, data-driven predictor, the linear minimum mean square error
predictor, for a near-infrared AO system under varying conditions. Our results
show varying wind can have a significant impact on the performance of wavefront
prediction, preventing it from reaching optimal performance. The impact depends
on the strength of the wind fluctuations with the greatest loss in expected
performance being for high wind speeds.Comment: 10 pages, 8 figures; Accepted to JOSA A March 201
Battle of the Predictive Wavefront Controls: Comparing Data and Model-Driven Predictive Control for High Contrast Imaging
Ground-based high contrast exoplanet imaging requires state-of-the-art
adaptive optics (AO) systems in order to detect extremely faint planets next to
their brighter host stars. For such extreme AO systems (with high actuator
count deformable mirrors over a small field of view), the lag time of the
correction (which can impact our system by the amount the wavefront has changed
by the time the system is able to apply the correction) which can be anywhere
from ~1-5 milliseconds, can cause wavefront errors on spatial scales that lead
to speckles at small angular separations from the central star in the final
science image. One avenue for correcting these aberrations is predictive
control, wherein previous wavefront information is used to predict the future
state of the wavefront in one-system-lag's time, and this predicted state is
applied as a correction with a deformable mirror. Here, we consider two methods
for predictive control: data-driven prediction using empirical orthogonal
functions and the physically-motivated predictive Fourier control. The
performance and robustness of these methods have not previously been compared
side-by-side. In this paper, we compare these predictors by applying them as
post-facto methods to simulated atmospheres and on-sky telemetry, to
investigate the circumstances in which their performance differs, including
testing them under different wind speeds, C_n^2 profiles, and time lags. We
also discuss future plans for testing both algorithms on the Santa Cruz Extreme
AO Laboratory (SEAL) testbed
SHIMM as an atmospheric profiler on the Nickel Telescope
Optimal atmospheric conditions are beneficial for detecting exoplanets via
high contrast imaging (HCI), as speckles from adaptive optics' (AO's) residuals
can make it difficult to identify exoplanets. While AO systems greatly improve
our image quality, having access to real-time estimates of atmospheric
conditions could also help astronomers use their telescope time more
efficiently in the search for exoplanets as well as aid in the data reduction
process. The Shack-Hartmann Imaging Motion Monitor (SHIMM) is an atmospheric
profiler that utilizes a Shack-Hartmann wavefront sensor to create spot images
of a single star in order to reconstruct important atmospheric parameters such
as the Fried parameter (), profile and coherence time. Due to its
simplicity, the SHIMM can be directly used on a telescope to get in situ
measurements while observing. We present our implementation of the Nickel-SHIMM
design for the one meter Nickel Telescope at Lick Observatory. We utilize an
HCIPy simulation of turbulence propagating across a telescope aperture to
verify the SHIMM data reduction pipeline as we begin on-sky testing. We also
used on-sky data from the AO system on the Shane Telescope to further validate
our analysis, finding that both our simulation and data reduction pipeline are
consistent with previously determined results for the Fried parameter at the
Lick Observatory. Finally, we present first light results from commissioning of
the Nickel-SHIMM.Comment: Conference Proceedings for 2023 SPIE Optics and Photonics, Techniques
and Instrumentation for Detection of Exoplanets X
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
Integrated photonic-based coronagraphic systems for future space telescopes
The detection and characterization of Earth-like exoplanets around Sun-like
stars is a primary science motivation for the Habitable Worlds Observatory.
However, the current best technology is not yet advanced enough to reach the
10^-10 contrasts at close angular separations and at the same time remain
insensitive to low-order aberrations, as would be required to achieve
high-contrast imaging of exo-Earths. Photonic technologies could fill this gap,
potentially doubling exo-Earth yield. We review current work on photonic
coronagraphs and investigate the potential of hybridized designs which combine
both classical coronagraph designs and photonic technologies into a single
optical system. We present two possible systems. First, a hybrid solution which
splits the field of view spatially such that the photonics handle light within
the inner working angle and a conventional coronagraph that suppresses
starlight outside it. Second, a hybrid solution where the conventional
coronagraph and photonics operate in series, complementing each other and
thereby loosening requirements on each subsystem. As photonic technologies
continue to advance, a hybrid or fully photonic coronagraph holds great
potential for future exoplanet imaging from space.Comment: Conference Proceedings of SPIE: Techniques and Instrumentation for
Detection of Exoplanets XI, vol. 12680 (2023
Visible extreme adaptive optics on extremely large telescopes: Towards detecting oxygen in Proxima Centauri b and analogs
Looking to the future of exo-Earth imaging from the ground, core technology
developments are required in visible extreme adaptive optics (ExAO) to enable
the observation of atmospheric features such as oxygen on rocky planets in
visible light. UNDERGROUND (Ultra-fast AO techNology Determination for
Exoplanet imageRs from the GROUND), a collaboration built in Feb. 2023 at the
Optimal Exoplanet Imagers Lorentz Workshop, aims to (1) motivate oxygen
detection in Proxima Centauri b and analogs as an informative science case for
high-contrast imaging and direct spectroscopy, (2) overview the state of the
field with respect to visible exoplanet imagers, and (3) set the instrumental
requirements to achieve this goal and identify what key technologies require
further development.Comment: SPIE Proceeding: 2023 / 12680-6
Recommended from our members
Laboratory demonstration of optimal identification and control of tip-tilt systems
Predictive wavefront control on Keck II adaptive optics bench: on-sky coronagraphic results
The behavior of an adaptive optics (AO) system for ground-based high contrast
imaging (HCI) dictates the achievable contrast of the instrument. In conditions
where the coherence time of the atmosphere is short compared to the speed of
the AO system, the servo-lag error can become the dominant error term of the AO
system. While the AO system measures the wavefront error and subsequently
applies a correction (typically taking a total of one or a few milliseconds),
the atmospheric turbulence above the telescope has changed resulting in the
servo-lag error. In addition to reducing the Strehl ratio, the servo-lag error
causes a build-up of speckles along the direction of the dominant wind vector
in the coronagraphic image, severely limiting the contrast at small angular
separations. One strategy to mitigate this problem is to predict the evolution
of the turbulence over the delay time. Our predictive wavefront control
algorithm minimizes, in a mean square sense, the wavefront error over the delay
and has been implemented on the Keck II AO bench. In this paper, we report on
the latest results of our algorithm and discuss updates to the algorithm
itself. We explore how to tune various filter parameters based on both daytime
laboratory tests and on-sky tests. We show a reduction in the
residual-mean-square wavefront error for the predictor compared to the leaky
integrator (the standard controller for Keck) implemented on Keck for three
separate nights. Finally, we present contrast improvements for daytime and
on-sky tests for the first time. Using the L-band vortex coronagraph for Keck's
NIRC2 instrument, we find a contrast gain of up to 2 at a separation of 3
lambda/D and up to 3 for larger separations (3-7 lambda/D).Comment: Accepted to JATIS May 20 2022. 34 pages, 15 Figures. arXiv admin
note: substantial text overlap with arXiv:2108.0893
Patient and Staff Experience of Remote Patient Monitoring—What to Measure and How: Systematic Review
BackgroundPatient and staff experience is a vital factor to consider in the evaluation of remote patient monitoring (RPM) interventions. However, no comprehensive overview of available RPM patient and staff experience–measuring methods and tools exists.
ObjectiveThis review aimed at obtaining a comprehensive set of experience constructs and corresponding measuring instruments used in contemporary RPM research and at proposing an initial set of guidelines for improving methodological standardization in this domain.
MethodsFull-text papers reporting on instances of patient or staff experience measuring in RPM interventions, written in English, and published after January 1, 2011, were considered for eligibility. By “RPM interventions,” we referred to interventions including sensor-based patient monitoring used for clinical decision-making; papers reporting on other kinds of interventions were therefore excluded. Papers describing primary care interventions, involving participants under 18 years of age, or focusing on attitudes or technologies rather than specific interventions were also excluded. We searched 2 electronic databases, Medline (PubMed) and EMBASE, on February 12, 2021.We explored and structured the obtained corpus of data through correspondence analysis, a multivariate statistical technique.
ResultsIn total, 158 papers were included, covering RPM interventions in a variety of domains. From these studies, we reported 546 experience-measuring instances in RPM, covering the use of 160 unique experience-measuring instruments to measure 120 unique experience constructs. We found that the research landscape has seen a sizeable growth in the past decade, that it is affected by a relative lack of focus on the experience of staff, and that the overall corpus of collected experience measures can be organized in 4 main categories (service system related, care related, usage and adherence related, and health outcome related). In the light of the collected findings, we provided a set of 6 actionable recommendations to RPM patient and staff experience evaluators, in terms of both what to measure and how to measure it. Overall, we suggested that RPM researchers and practitioners include experience measuring as part of integrated, interdisciplinary data strategies for continuous RPM evaluation.
ConclusionsAt present, there is a lack of consensus and standardization in the methods used to measure patient and staff experience in RPM, leading to a critical knowledge gap in our understanding of the impact of RPM interventions. This review offers targeted support for RPM experience evaluators by providing a structured, comprehensive overview of contemporary patient and staff experience measures and a set of practical guidelines for improving research quality and standardization in this domain
Functional assessment of mouse complement pathway activities. and quantification of C3b/C3c/iC3b in an experimental model of mouse renal ischaemia/reperfusion injury
The complement system is an essential component of our innate immunity, both for the protection against infections and for proper handling of dying cells. However, the complement system can also contribute to tissue injury and inflammatory responses. In view of novel therapeutic possibilities, there is an increasing interest in measurement of the complement system activation in the systemic compartment, both in the clinical setting as well as in experimental models. Here we describe in parallel a sensitive and specific sandwich ELISA detecting mouse C3 activation fragments C3b/C3c/iC3b, as well as functional complement ELISAs detecting specific activities of the three complement pathways at the level of C3 and at the level of C9 activation. In a murine model of renal ischaemia/reperfusion injury (IRI) we found transient complement activation as shown by generation of C3b/C3c/iC3b fragments at 24 h following reperfusion, which returned to base-line at 3 and 7 days post reperfusion. When the pathway specific complement activities were measured at the level of C3 activation, we found no significant reduction in any of the pathways. However, the functional complement activity of all three pathways was significantly reduced when measured at the level of C9, with the strongest reduction being observed in the alternative pathway. For all three pathways there was a strong correlation between the amount of C3 fragments and the reduction in functional complement activity. Moreover, at 24 h both C3 fragments and the functional complement activities showed a correlation with the rise in serum creatinine. Together our results show that determination of the systemic pathway specific complement activity is feasible in experimental mouse models and that they are useful in Understanding complement activation and inhibition in vivo. (C) 2015 Elsevier B.V. All rights reserved