Anisoplanatism in adaptive optics

Fried, David L.

doi:10.1364/josa.72.000052

Cited by 396 publications

(206 citation statements)

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“…Therefore, the adaptive optics (AO) system of the NSO/DST (Rimmele et al 2004) achieved a good performance in terms of stability and resolution in the centre of the field of view (FOV). In this work, we use only of the central part of the IBIS FOV, since the spatial resolution and the image contrast degrade towards the edge of the FOV owing to the strong anisoplanatism (Fried 1982).…”

Section: Observations and Data Processingmentioning

confidence: 99%

Magnetic and velocity fields of a solar pore

Sobotka

Moro

Jurčák

et al. 2012

A&A

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Context. Solar pores are intermediate-size magnetic flux features that emerge at the surface of the Sun. The absence of a filamentary penumbra indicates that there is a relatively simple magnetic structure with a prevailing vertical magnetic field. Aims. Relations between the magnetic field components, line-of-sight velocities, and horizontal motions in and around a large pore (D eff = 8. 5) are analysed to provide observational constraints on theoretical models and numerical simulations. Methods. Spectropolarimetric observations in Fe I 617.3 nm of the pore NOAA 11005 with the IBIS spectrometer attached to the Dunn Solar Telescope are inverted into series of maps of thermal, magnetic, and velocity parameters using the SIR code. Horizontal velocities are obtained from series of white-light images by means of local correlation tracking. Results. The magnetic field B extends from the visible pore border of more than 3. 5 and has a radial structure in a form of spines that are co-spatial with dark intergranular lanes. The horizontal component B hor is more extended than the vertical component B z . The temperature linearly decreases with increasing B z , by about −300 K kG −1 in the photosphere and −800 K kG −1 in the umbra. The temperature contrast of granulation increases with increasing magnetic field strength and is then suppressed for B z > 1200 G. Granular upflows dominate in regions with B z < 600-700 G. Line-of-sight velocities are lower in stronger fields, except for fast isolated downflows at the pore's border. The velocity signature of granulation is suppressed completely for B hor > 1000 G. Horizontal motions of granules start to be damped for B z > 500 G and recurrently exploding granules appear only in magnetic fields comparable to or weaker than the equipartition field strength 400 G.

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Section: Observations and Data Processingmentioning

confidence: 99%

Magnetic and velocity fields of a solar pore

Sobotka

Moro

Jurčák

et al. 2012

A&A

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“…Resulting from the different turbulence encountered by the light propagation from the AO reference source and the scientific target, anisoplanatism is known to limit the correction quality of SCAO beyond the isoplanatic patch (Fried 1982). Several studies have been published about the effect of anisoplanatism on the AO performance in terms of the PSF Strehl ratio (SR) and include the influence of different turbulence characteristics: turbulence profile, outer scale, etc.…”

Section: Introductionmentioning

confidence: 99%

Anisoplanatism effect on the E-ELT SCAO point spread function. A preserved coherent core across the field

Clénet

Gendron

Gratadour

et al. 2015

A&A

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Context. The science case studies and the optimized designing of the future adaptive optics-fed extremely large telescope instruments require the precise simulation of their adaptive optics system, potentially over their whole field of view, whatever the adaptive optics flavor the instruments will be equipped with. Aims. We simulate the anisoplanatism effect on the extremely large telescope single conjugate adaptive optics point spread function. Our interest in this expected degradation of the correction performance with respect to the off-axis distance is in terms of the point spread function Strehl ratio and profile. Methods. Adaptive optics simulations at the scale of extremely large telescopes are challenging given the large parameter space to explore for the adaptive optics dimensioning and the large number of degrees of freedom at play for a given set of simulation parameters. To address this problem, we have used three different simulation tools with increasing degree of fidelity compared to a real adaptive optics system. The first is based on analytical formulae and allowed us to derive the Strehl ratio degradation with the off-axis distance. The second is a Fourier-based code and provided us with both the Strehl ratio and the point spread function profile in the field. The last is an end-to-end code based on the graphical processing unit technology and also provided us with the Strehl ratio and the point spread function profile in the field. Results. The three tools we used demonstrated a fast execution time even at the extremely large telescope scale. Cross-checks between the different codes were performed and demonstrated the coherency of the results. In addition to the expected degradation of the adaptive optics performance with the field angle, we demonstrated that in the simulation conditions applicable to the E-ELT, the single conjugate adaptive optics point spread function remains topped with a coherent core even at off-axis distances as large as 60 arcsec and consequently very low Strehl ratios. We also studied the impact of the outer scale on the point spread function profile, demonstrating that the aforementioned Airy-like pattern is observable even when the outer scale is larger than the telescope diameter. Conclusions. These results could push for the preservation over a large field of the optical quality of any common path optics between the telescope and the instruments in single conjugate adaptive optics mode. This could offer some astrometric capabilities to these instruments operating in this adaptive optics mode.

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“…Outer scale L 0 is a C 2 n -weighted average of the local turbulence outer scale L 0 (h), as defined by Borgnino (1990). The isoplanatic angle θ 0 is relevant for adaptive optics (Fried 1982).…”

Section: Introductionmentioning

confidence: 99%

Optical parameters relevant for High Angular Resolution at Paranal from GSM instrument and surface layer contribution

Martin

Conan

Tokovinin³

et al. 2000

Astron. Astrophys. Suppl. Ser.

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Abstract. Main atmospheric parameters characterizing the turbulence were measured at the Paranal ESO Observatory (Chile) with the Generalized Seeing Monitor (GSM) during 19 nights in November-December 1998. The median seeing for this period was 0.88 , a little worse than average, the spatial coherence outer scale of the wavefront L 0 = 22.0 m and the median isoplanatic angle θ 0 = 1.90 . A very good agreement with seeing values given by ESO DIMM was found. Effects of ground layer turbulence were estimated from measurements of temperature micro-fluctuations at several altitudes. These measurements revealed that the first 21 m above ground account for 12.5% of the total turbulent energy. Comparison between GSM and ESO DIMM values have permitted to highlight a local phenomenon which occurs sometimes at the site in the middle of the night. Statistics of the refractive index structure constant C 2 n in the surface layer is also studied.

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Anisoplanatism in adaptive optics

Cited by 396 publications

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Magnetic and velocity fields of a solar pore

Magnetic and velocity fields of a solar pore

Anisoplanatism effect on the E-ELT SCAO point spread function. A preserved coherent core across the field

Optical parameters relevant for High Angular Resolution at Paranal from GSM instrument and surface layer contribution

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