  Advances in micro deformable mirror (DM) technologies such as MEMs, have
stimulated interest in the characteristics of systems that include a high
stroke mirror in series with a high actuator count mirror. This arrangement is
referred to as a woofer-tweeter system. In certain situations it may be
desirable or necessary to operate the woofer DM in open-loop. We present a
simple method for controlling a woofer DM in open loop provided the device
behaves in an approximately linear fashion. We have tested a mirror that we
believe meets our criterion, the ALPAO DM52 mirror. Using our open-loop method
we fit several test Kolmogorov wavefronts with the mirror and have achieved an
accuracy of approximately 25 nm rms surface deviation over the whole clear
aperture, and 20 nm rms over 90% of the aperture. We have also flattened the
mirror in open loop to approximately 11 nm rms residual.
