LGS alternative wave-front sensing: Projected Pupil Plane Pattern (PPPP)

Yang, Huizhe; Basden, Alastair; Buscher, David F.; Juez, Francisco Javier de Cos; Kellerer, Aglae; Morris, Tim; Myers, R; Younger, Eddy; Bharmal, Nazim Ali

doi:10.1117/12.2311991

Cited by 3 publications

(2 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…2 Therefore, CfAI has been funded to test in situ at two non-LGS concepts: correlating Shack Hartmann on back-scattered laser speckle, via Rayleigh scattering, to approximate a continuum of randomly placed guide stars, and the PPPP concept. 3 The fundamental idea behind the speckle concept is power density is diluted which permits powerful lasers without safety risks together with wavelength which is not restricted by the scattering mechanism unlike Na resonance. Meanwhile the PPPP concept has been extensively tested in simulation 3 and in the laboratory 4 * and application of machine learning leads to much improvement in SNR-lower laser power-and potentially considerably simplified implementation (single plane rather than dual plane).…”

Section: Introductionmentioning

confidence: 99%

WIVERN: a laboratory experiment for testing novel laser-based wavefront sensing techniques

Bharmal

Bramall

Rosario³

et al. 2022

Adaptive Optics Systems VIII

View full text Add to dashboard Cite

WIVERN is a testbed for laboratory experiments in laser-based wavefront sensing. It emulates laser uplink from a 4 m telescope with 1.6 arcsec seeing and laser back-scattering from up to 20 km. Currently there are three current wavefront sensing capabilities. The first two are from a wide-field of view (1.0 arcmin) Shack Hartmann wavefront sensor observing a constellation of point sources at infinity (reference targets, star-oriented wavefront sensing), or an image from emulated back-scattering (wide-field correlation wavefront sensing). The third is based on the PPPP concept. Other sub-systems are laser projection replicating a pupil launch, a 7x7 pupil-conjugate deformable mirror (DM), and a wide-field camera for PSF analysis. A 500 Hz rate accumulates sufficient data for statistical and machine-learning analysis over hour timescales. It is a compact design (2.1 m 2 ) with mostly commercial dioptric components. The sub-system optical interfaces are identical: a flat focal plane for easy bench reconfiguration. The end-to-end design is diffraction-limited with ≤ 1% pupil distortion for wavelengths λ=633-750 nm.

show abstract

Section: Introductionmentioning

confidence: 99%

WIVERN: a laboratory experiment for testing novel laser-based wavefront sensing techniques

Bharmal

Bramall

Rosario³

et al. 2022

Adaptive Optics Systems VIII

View full text Add to dashboard Cite

show abstract

“…Third, the wavefront reconstruction does not employ tomography nor require a priori knowledge of the turbulence profile. PPPP has been demonstrated as an effective solution to focus anisoplanatism using simulation and laboratory experiments, Yang et al (2018a) and Yang et al (2018b) respectively, and can achieve equivalent performance to a Shack-Hartmann (SH) WFS using a natural guide star. However, the linear reconstruction method used so far performs poorly when including photon noise (dependent on laser power) and detector read noise.…”

Section: Introductionmentioning

confidence: 99%

Projected Pupil Plane Pattern (PPPP) with artificial Neural Networks

Yang

González-Gutiérrez

Bharmal

et al. 2019

Monthly Notices of the Royal Astronomical Society

Self Cite

View full text Add to dashboard Cite

Focus anisoplanatism is a significant measurement error when using one single laser guide star (LGS) in an Adaptive Optics (AO) system, especially for the next generation of extremely large telescopes. An alternative LGS configuration, called Projected Pupil Plane Pattern (PPPP) solves this problem by launching a collimated laser beam across the full pupil of the telescope. If using a linear, modal reconstructor, the high laser power requirement (∼ 1000 W) renders PPPP uncompetitive with Laser Tomography AO. This work discusses easing the laser power requirements by using an artificial Neural Network (NN) as a non-linear reconstructor. We find that the non-linear NN reduces the required measurement signal-to-noise ratio (SNR) significantly to reduce PPPP laser power requirements to ∼ 200 W for useful residual wavefront error (WFE). At this power level, the WFE becomes 160 nm root mean square (RMS) and 125 nm RMS when r 0 = 0.098 m and 0.171 m respectively for turbulence profiles which are representative of conditions at the ESO Paranal observatory. In addition, it is shown that as a non-linear reconstructor, a NN can perform useful wavefront sensing using a beam-profile from one height as the input instead of the two profiles required as a minimum by the linear reconstructor.

show abstract