Phase sensor for solar adaptive-optics

Context. Wavefront sensing in solar adaptive-optics is currently done with correlating Shack-Hartmann sensors, although the spatialand temporal-resolutions of the phase measurements are then limited by the extremely fast computing required to correlate the sensor signals at the frequencies of daytime atmospheric-fluctuations. Aims. To avoid this limitation, a new wavefront-sensing technique is presented, that makes use of the solar brightness and is applicable to extended sources. Methods. The wavefront is sent through a modified Mach-Zehnder interferometer. A small, central part of the wavefront is used as reference and is made to interfere with the rest of the wavefront. Results. The contrast of two simultaneously measured interference-patterns provides a direct estimate of the wavefront phase, no additional computation being required. The proposed optical layout shows precise initial alignment to be the critical point in implementing the new wavefront-sensing scheme. Conclusions.

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Pupil inversion Mach-Zehnder interferometry for diffraction-limited optical astronomical imaging

Prieto-Blanco

Liñares

Montero-Orille

et al. 2020

Opt. Express

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We present theoretical and laboratory experimental results on a robust interferometric device based on pupil inversion, or 180° rotational shearing interferometry. The image of an astronomical object degraded by the atmosphere turbulence can be restored (ideally up to the diffraction limit) by a numerical post-processing of the interferogram. Unlike previous Michelson configurations that return half of the light to the sky, the Mach-Zehnder interferometer has no fundamental losses when both outputs are used. The interferogram is formed by two overlapped images of the telescope pupil, but one of them is spatially inverted, and out of phase by π/2 only in its half. This optical operation is achieved in a robust way by inserting a refractive optical image inverter and a binary phase plate in one of the arms of the interferometer. In this way, the system has no polarization dependence or moving parts since the plate allows the object to be retrieved numerically from just one interferogram (single exposition) or a few independent interferograms. For that, several algorithms are proposed. Likewise, we include a laboratory proof-of-concept in which a diffraction-limited image is obtained in spite of presence of aberrations and photon noise.

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Phase sensor for solar adaptive-optics

Cited by 3 publications

References 10 publications

Solar adaptive optics: specificities, lessons learned, and open alternatives

Solar adaptive optics: specificities, lessons learned, and open alternatives

Phase sensor for solar adaptive-optics

Pupil inversion Mach-Zehnder interferometry for diffraction-limited optical astronomical imaging

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