12 August 2010 Impact of spatial resolution on thermal blooming phase compensation instability
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Phase compensation instability (PCI) is the time-dependent development of spatial perturbations that occur within thermally bloomed high-energy laser (HEL) beams. These types of spatial perturbations act as local hot spots that create small negative lenses within the HEL beam. Closed-loop adaptive optics (AO) corrects for these spatial perturbations by applying small positive-lens phase compensations, which only increases the strength of the local hot spots and leads to runaway in the adaptive-optics servo. This study uses a straightforward wave-optics code to model horizontal propagation with the effects of thermal blooming for a focused Gaussian beam. The strength of the thermal blooming effects is characterized using the classic dimensionless distortion number. A nominal AO system is used to mitigate phase distortions accumulated from thermal blooming. Parameters within the AO system, such as the number of actuators on the deformable mirror and the resolution of the wavefront sensor, are varied to determine the impact of spatial resolution in the development of the PCI. A discussion is given on the potential use of control theory to diminish the effects of the PCI.
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Mark F. Spencer, Mark F. Spencer, Salvatore J. Cusumano, Salvatore J. Cusumano, Jason D. Schmidt, Jason D. Schmidt, Steven T. Fiorino, Steven T. Fiorino, "Impact of spatial resolution on thermal blooming phase compensation instability", Proc. SPIE 7816, Advanced Wavefront Control: Methods, Devices, and Applications VIII, 781609 (12 August 2010); doi: 10.1117/12.859936; https://doi.org/10.1117/12.859936

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