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The adaptive optics (AO) system requires natural guide stars to differentiate the focus error generated by the vertical shift in the sodium centroid altitude together with atmospheric turbulence. This dependency on NGS restricts achieving usable sky coverage and AO operation during dawn. One of the proposed approaches to distinguishing these two focus errors is to continuously monitor the region of the sodium layer where the laser guide star (LGS) is generated. The classical approaches used for this task, direct imaging and LIDAR technology, have limitations on spatial resolution and equipment requirements. The technique of continuously amplitude modulating the guidestar laser (GSL) according to the pseudo-random binary sequence (PRBS) has the potential to overcome the limitations of classical approaches and reduce the dependency of the AO system on the NGS. However, for this technique to be implemented in AO systems, it must be validated at different modulation strengths and modulation frequencies that satisfy the system requirements. Therefore, I conducted a study to experimentally verify the PRBS modulation technique for LGS applications. The study began with numerical simulations considering the parameters of two potential test sites in Australia: the 1.8-m EOS telescope at Mount Stromlo in Canberra and the 2.3-m ANU telescope at Siding Spring Observatory in Coonabarabran. The numerical simulation study was extended to large and extremely large telescopes. Based on the system design and the on-sky requirement to validate the technique with two potential test sites in Australia, hardware components were chosen, procured, and characterized in the laboratory. An experiment was conducted to validate the technique in the laboratory with the chosen hardware. The study validated that the PRBS technique has the potential to overcome the monitoring of the sodium layer with classical approaches with high-power lasers. |
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