Benchtop implementation of branch-point-tolerant adaptive optics

We use a benchtop atmospheric turbulence simulator (ATS) and adaptive-optics (AO) system to experimentally evaluate AO performance using a Shack--Hartmann wavefront sensor (SHWFS) and digital-holographic wavefront sensor (DHWFS). Consistent with past results, we show that while the SHWFS yields performance improvement relative to no AO compensation, the SHWFS struggles in strong scintillation conditions. However, when we control our AO system using the least-squares component of our DHWFS measurements, we notice a substantial improvement in performance relative to the results we obtain with the SHWFS. We also leverage our DHWFS measurements to implement a post-processing congruence operation algorithm, referred to as the least-squares principal value (LSPV). We show that the LSPV-based results yield substantial AO performance improvements in strong scintillation conditions compared to only using the least-squares component of our DHWFS measurements. LSPV enables partial compensation of the hidden-phase component---a requirement to achieve better AO performance when scintillation is strong. These findings will be of interest to researchers exploring AO performance in deep turbulence and those who are interested in branch-point-tolerant AO approaches.