Novel wavefront sensing strategies for strong atmospheric turbulence

Atmospheric effects limit the performance of any electro-optical (EO) system. Tasks such as laser communication and delivery of directed energy are significantly affected by turbulence and refraction. A correction of atmospheric effects on the propagation of light can be done by adaptive optics (AO). Especially for astronomical applications, AO technology shows great promise for improving the performance of EO-systems. Nevertheless, challenging scenarios like a long horizontal path or strong scintillation lead to high failure rates of the EO systems. Adaptive optics methods and components developed for astronomical applications cannot fulfil these higher requirements. Unconventional wavefront sensors and sensing strategies are developed at Fraunhofer IOSB to provide alternatives for measuring the wavefront deformation of a laser beam and to improve the performance of laser communications and directed-energy weapons even in strong turbulence and/or horizontal-path propagation. In this paper we show the realization of the holographic wavefront sensor (HWFS) and we present results from two ""wavefront-sensorless"" approaches: stochastic parallel gradient descent (SPGD) and its modal version (M-SPGD).