Computationally efficient autoregressive method for generating phase screens with frozen flow and turbulence in optical simulations

Srinath, Srikar; Poyneer, Lisa; Rudy, Alexander R.; Ammons, S. Mark

doi:10.1364/oe.23.033335

Cited by 22 publications

(8 citation statements)

References 26 publications

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“…We do not consider the effects of residual uncorrected aberrations (i.e., the phase screen PSD amplitude and shape should be significantly larger, on the order of tens of microns rms, and closer to -11/3, respectively, beyond the spatial frequencies corresponding to the DM control radius) and therefore will not analyze performance beyond the 16 λ/D control radius. We use the framework from Srinath et al (2015), where the α parameter, a dimensionless number between 0 and 1, is used to simulate atmospheric "boiling," or deviating random effects from pure frozen flow; e.g., α = 0.95 means that 95% of the current phase screen (or 100 2 (0.95) ≈97 nm rms) will be translated to the next phase screen realization via a Fourier shift based on the time interval, telescope diameter, and wind speed and direction, whereas as the other 100 2 (1 − 0.95) ≈22 nm rms component of the next phase screen realization will be randomly generated, but with the same -2 power law. In this paper we use a windspeed of 10 m/s in the +x pupil direction, 1 ms time intervals, and α = 0.95 (i.e., 5% random turbulence is added every ms).…”

Section: A2 Post-processing Algorithmsmentioning

confidence: 99%

Fast Coherent Differential Imaging on Ground-based Telescopes Using the Self-coherent Camera

Gerard

Marois

Galicher

2018

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Direct imaging and spectral characterization of exoplanets using extreme adaptive optics (ExAO) is a key science goal of future extremely large telescopes and space observatories. However, quasi-static wavefront errors will limit the sensitivity of this endeavor. Additional limitations for ground-based telescopes arise from residual AOcorrected atmospheric wavefront errors, generating millisecond-lifetime speckles that average into a halo over a long exposure. A solution to both of these problems is to use the science camera of an ExAO system as a wavefront sensor to perform a fast measurement and correction method to minimize these aberrations as soon as they are detected. We develop the framework for one such method based on the self-coherent camera (SCC) to be applied to ground-based telescopes, called Fast Atmospheric SCC Technique (FAST). We show that with the use of a specially designed coronagraph and coherent differential imaging algorithm, recording images every few milliseconds allows for a subtraction of atmospheric and static speckles while maintaining a close to unity algorithmic exoplanet throughput. Detailed simulations reach a contrast close to the photon noise limit after 30 seconds for a 1% bandpass in H band on both 0 th and 5 th magnitude stars. For the 5th magnitude case, this is about 110 times better in raw contrast than what is currently achieved from ExAO instruments if we extrapolate for an hour of observing time, illustrating that sensitivity improvement from this method could play an essential role in the future detection and characterization of lower mass exoplanets.

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Section: A2 Post-processing Algorithmsmentioning

confidence: 99%

Fast Coherent Differential Imaging on Ground-based Telescopes Using the Self-coherent Camera

Gerard

Marois

Galicher

2018

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“…The atmospheric coherence length is a parameter of the simulation, which we use to adjust the average Strehl ratio of the PSF delivered by the AO correction. Our particular implementation of Kolmogorov turbulence employs the Fourier-based autoregressive algorithm of [26]; an example aberrated wavefront in the pupil plane generated with this method is shown in Fig. 3a.…”

Section: Wavefront Errormentioning

confidence: 99%

Design considerations of photonic lanterns for diffraction-limited spectrometry

2021

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The coupling of large telescopes to astronomical instruments has historically been challenging due to the tension between instrument throughput and stability. Light from the telescope can either be injected wholesale into the instrument, maintaining high throughput at the cost of point-spread function (PSF) stability, or the time-varying components of the light can be filtered out with single-mode fibers (SMFs), maintaining instrument stability at the cost of light loss. Today, the field of astrophotonics provides a potential resolution to the throughput-stability tension in the form of the photonic lantern (PL): a tapered waveguide which can couple a timevarying and aberrated PSF into multiple diffraction-limited beams at an efficiency that greatly surpasses direct SMF injection. As a result, lantern-fed instruments retain the stability of SMF-fed instruments while increasing their throughput. To this end, we present a series of numerical simulations characterizing PL performance as a function of lantern geometry, wavelength, and wavefront error (WFE), aimed at guiding the design of future diffraction-limited spectrometers. These characterizations include a first look at the interaction between PLs and phase-induced amplitude apodization (PIAA) optics. We find that Gaussian-mapping beam-shaping optics can enhance coupling into 3-port lanterns but offer diminishing gains with larger lanterns. In theand -band (0.97-1.35 μm) region, with moderately high WFE (∼10% Strehl ratio), a 3-port lantern in conjunction with beam-shaping optics strikes a good balance between pixel count and throughput gains. If pixels are not a constraint, and the flux in each port will be dominated by photon noise, then larger port count lanterns will provide further coupling gains due to a greater resilience to tip-tilt errors. Finally, we show that lanterns can maintain high operating efficiencies over large wavelength bands where the number of guided modes at the lantern entrance drops, if care is taken to minimize the attenuation of weakly radiative input modes.

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“…The most recent algorithms for generating atmospheric phase disturbance in simulation have been proposed to minimize computation time [21] as well as include the effects of boiling [22]. They also have flexible architectures that allow for the wind speed, outerscale and Fried parameter to vary at each time step.…”

Section: Simulating Atmospheric Phasementioning

confidence: 99%

Impact of time-variant turbulence behavior on prediction for adaptive optics systems

2019

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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.

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Computationally efficient autoregressive method for generating phase screens with frozen flow and turbulence in optical simulations

Cited by 22 publications

References 26 publications

Fast Coherent Differential Imaging on Ground-based Telescopes Using the Self-coherent Camera

Fast Coherent Differential Imaging on Ground-based Telescopes Using the Self-coherent Camera

Design considerations of photonic lanterns for diffraction-limited spectrometry

Impact of time-variant turbulence behavior on prediction for adaptive optics systems

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