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

Abstract

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.

Temporal spectrum of multiconjugate adaptive optics residuals and impact of tip-tilt anisoplanatism on astrometric observations

“…𝑡𝑢𝑟 𝑏 is the CPSD of turbulence between the two directions and where we considered 𝑆 𝑡𝑢𝑟 𝑏 = 𝑆 𝛼 𝑡𝑢𝑟 𝑏 = 𝑆 𝛽 𝑡𝑢𝑟 𝑏 , having assumed a homogeneous and isotropic turbulence. The expression (integrated over the temporal frequencies) is in agreement with the results that are present in the literature (Sandler et al 1994;Clénet et al 2015).…”

The impact of ELT distortions and instabilities on future astrometric observations

“…1). In single-conjugate AO mode however, the Strehl and astrometric performance at the edge of an arcmin sized field would be seriously compromised by the telescope-induced platescale jitter, which would probably prevent from taking advantage of having an M1 aperture comparable to the outer scale of the atmosphere (Clénet (2015) estimated that even in SCAO the ELT NIR SCAO corrected PSF could have non-negligible Strehl).…”

Empirical Green's function approach for utilizing millisecond focal and pupil plane telemetry in exoplanet imaging

“…( 27) assumes that the effects of anisoplanatism are negligible, which should be valid for exoplanet imaging. 4,17 The quantity in braces in Eq. ( 27) the "planetary intensity kernel."…”