Non-linear Curvature Wavefront SensorA high sensitivity wavefront sensor for adaptive optics |
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Show content only (no menu, header)Non-linear Curvature Wavefront sensing1. PrincipleThe non-linear Curvature wavefront sensor (nlCWFS) uses 4 defocused pupil images to measure with great sensitivity wavefront aberrations. It is derived from phase diversity wavefront sensing. Thanks to the presence of diffraction-limited speckles in the defocused pupil images, the sensor measures wavefront errors with the sensitivity given by the diffraction limit of the telescope, instead of the sensitivity given by the seeing limit for most common wavefront sensors. A detailed description of the wavefront sensor and its performance can be found in this paper: "High Sensitivity Wavefront Sensing with a non-linear Curvature Wavefront Sensor" [pdf][astro-ph], Guyon, O. PASP, 122, pp.49-62 (2010).
2. Optical configuration2.1. Example of a possible optical layoutThe nlCWFS needs to produce 4 defocused images of the pupil. each conjugated to a different plane (2 images are conjugated ahead of the pupil, 2 images are conjugated after the pupil).
2.2. ChromaticityFor each of the 4 images, the distance between the plane to which the image is conjugated to be pupil plane needs to be inversely proportional to the wavelength. This is necessary to maintain sharp diffraction-limited speckles in broadband light.
3. Reconstruction algorithm3.1. Iterative GS-type reconstructionThe nlCWFS wavefront reconstruction requires a non-linear wavefront reconstruction algorithm. The iterative reconstruction algorithm used so far for nlCWFS research can be found on this webpage.3.2. Required computing powerThe reconstruction algorithm is performing iterative GS loops. In closed loop, approximately 10 loops are required per AO loop iteration. Assuming pupil is 32 pixels across, the required number of operations per GS iterations are:
This work is supported by the National Science Fundation (NSF) and the National Astronomical Observatory of Japan (NAOJ), and NASA. Page content last updated: 27/06/2023 06:35:52 HST html file generated 27/06/2023 06:34:36 HST |