AO4ELT5 Proceedings

Real-time Shack-Hartmann wavefront sensor reference scaling compensates for beacon size

Oliker, Michael D. (Leidos), Steinbock, Michael J. (Air Force Research Laboratory), Roskey, Daniel E. (Leidos), Reynolds, Odell R. (Air Force Research Laboratory), Buckman, Miles D. (Air Force Research Laboratory)

Past research in adaptive optics (AO) has demonstrated the link between apparent beacon extent and wavefront gradient estimation sensitivity of a classical Shack-Hartmann (SH) subaperture, particularly when using quad-cell detector regions. In most practical SH AO systems that utilize sodium beacon laser guide stars, the subaperture diameters are large enough to resolve beacon features. This is particularly relevant on larger telescope apertures where beacon elongation is present. Additionally, residual wavefront error can further broaden the subaperture point spread functions as the atmospheric seeing varies in time. This paper presents research conducted at the Starfi re Optical Range over the past 8 years in implementing a robust solution on the site's 3.5m telescope and AO system. Emphasis is given towards the practical aspects that must be considered beyond the pure theory, which has been presented in several prior works. A high signal-to-noise strategy has been implemented that estimates the aperture-averaged subaperture sensitivity (related to beacon size) in real-time by exploiting the null-space of the least-squares wavefront reconstructor. Careful consideration has gone into the implementation of this estimation method to avoid unintended effects, particularly at low light levels. Moreover, consideration of how to best utilize the estimated subaperture sensitivity within the AO pipeline will be presented.

DOI: 10.26698/AO4ELT5.0174- Proceeding PDF

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