Abstract
The availability and performance of laser-based adaptive optics (AO) systems are strongly dependent on the power and quality of the laser beam before being projected to the sky. Frequent and time-consuming alignment procedures are usually required in the laser systems with free-space optics to optimize the beam. Despite these procedures, significant distortions of the laser beam have been observed during the first two years of operation of the Gemini South multi-conjugate adaptive optics system (GeMS). A beam shaping concept with two deformable mirrors is investigated in order to provide automated optimization of the laser quality for astronomical AO. This study aims at demonstrating the correction of quasi-static aberrations of the laser, in both amplitude and phase, testing a prototype of this two-deformable mirror concept on GeMS. The paper presents the results of the preparatory study before the experimental phase. An algorithm to control amplitude and phase correction, based on phase retrieval techniques, is presented with a novel unwrapping method. Its performance is assessed via numerical simulations, using aberrations measured at GeMS as reference. The results predict effective amplitude and phase correction of the laser distortions with about 120 actuators per mirror and a separation of 1.4 m between the mirrors. The spot size is estimated to be reduced by up to 15% thanks to the correction. In terms of AO noise level, this has the same benefit as increasing the photon flux by 40%.
Highlights
This study aims at demonstrating the correction of quasi-static aberrations of the laser, in both amplitude and phase, testing a prototype of this two-deformable mirror concept on Gemini South multi-conjugate adaptive optics system (GeMS)
From Eq (1), if the image spot size θimage is reduced by 15%, it is equivalent for a given adaptive optics (AO) noise level to increase the number of photons by 40%
A two-deformable-mirror concept is developed to optimize the beam shape of the laser used as beacons for adaptive optics in astronomy
Summary
The performance of adaptive optics (AO) is strongly dependent on the quality of the wavefront sensing measurements from the guide stars because they directly affect the correction error [1]. A slow increase of the M2 values over the length of the runs has been noticed, suggesting that the system suffers from constant misalignment [4] The impact of this degraded shape of the beam on the laser intrinsic spot size has been previously quantified by including the measured irradiance of April 2013 (top of Fig. 1) in simulations of the uplink propagation of the laser from the launching telescope to the mesosphere [7]. The atmospheric wavefront distortion would be known thanks to the adaptive optics of the telescope (represented by AO sensing device in Fig. 2(b)), for which the receiving aperture is the primary mirror and does not coincide with the launching telescope Demonstration of such capability is yet unknown to the authors, so such dynamical extension of the correction is left for further research. Its weighting can be updated on the fly with every new field estimate and no precomputation of pseudo-inverse matrix is required
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
