Characterization of the holographic wavefront sensor for free-space optical communications

We are studying the effectiveness of HWFS for measuring the first few low-order aberrations. In literature a value of 10%Strehl ratio has been assumed as a threshold of usefulness of adaptive-optics correction for laser communications. We want to check whether such a value can be achieved through the use of HWFS for compensation of laser beams over long horizontal paths. We realized HWFS by recording an analog multiplex hologram. We analyzed the sensor's response to incoming laser beams with defined wavefront aberrations. The test wavefronts were aberrated with the deformable mirror DM-52-15 by ALPAO. We studied the influence of tip/tilt on the senor's accuracy. The effect of a tilted laser beam on HWFS is an unsymmetrical misalignment of the reconstructed spots. In this case the use of small photodiodes for intensity measurement- a configuration recommended for tip/tilt-free beam - can lead to error-prone measurements.