10 July 2008 LGS wavefront sensing using adaptive beam projectors
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The paper presents a new technique to improve the wavefront sensing process when LGSs are used. The technique starting point is to shrink to LGS projected spot by using a low order AO system located at the laser projector. This AO system is used to pre-correct the beam so that LGS spot on the sodium layer can have a diffraction limited FWHM. In this case the reconstruction error due to photon noise and so the laser power is reduced by the square of the ratio between the uncorrected and corrected projected spot FWHMs. The paper analyzes the LGS spot dimension as seen from the main telescope to quantify the final gain in the wavefront sensing process of the main AO system. The following analysis is done for a Shack Hartmann sensor with 16x16 subapertures and correcting for 210 modes and for a Pyramid Sensor (PS) having 32x32 subapertures and correcting for 666 modes. The achieved results in term of laser power gain ranges between 1.5-3 and between 3-6 for the SH and PS respectively. These gains are achieved at the expenses of making the laser projector adaptive. Finally some discussion of the impact achieved using the considered technique and gains is presented at the end of the paper.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
S. Esposito and L. Busoni "LGS wavefront sensing using adaptive beam projectors", Proc. SPIE 7015, Adaptive Optics Systems, 70151P (10 July 2008); doi: 10.1117/12.790644; https://doi.org/10.1117/12.790644

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