Closed-loop field conjugation using decentralized multi-conjugate adaptive optics

Imaging through turbulence using adaptive optics is limited by scintillation, even with perfect wavefront sensing and reconstruction. Such errors can be mitigated in closed loop by multi-conjugate adaptive optics systems consisting of two phase correctors, each of which is driven by a pair of wavefront sensor phase measurements, along with an internal probe beam that samples the beam train along a common path while propagating in the opposite direction as the external signal beam or beacon wavefront that samples the turbulence. With this arrangement, not only direct measurement and feedback of irradiance but also intensive and/or highly coupled nonlinear control algorithms can be avoided in favor of more conventional, simple, decentralized linear control laws. Linear stability analysis of such systems is feasible in spatial frequency domain, and nonlinear wave-optic simulations in time domain suggest that, given sufficient temporal bandwidth, rejection of combined phase and amplitude disturbances can be enhanced by a factor of two or more (as quantified by error variances or Strehl ratio logarithms). Previous studies by other authors are extended using simplified regularization methods.