The random phase screen transfer function is a useful tool to control the surface figure of optical components. Theory
and proposed algorithms, tie in to lens design codes, and example specifications are reviewed.
The Phased Array Mirror, Extendible Large Aperture telescope has been fully assembled and testing has started. The telescope is the first to have a fully adaptive primary mirror, which consists of 36 hexagonal injection-molded Pyrex segments that are seven centimeters flat-to- flat. The segments are mounted on three long-throw voice-coil actuators for tip, tilt, and piston motion. The segment tiles are measured with a Hartmann-Shack wavefront sensor and the piston errors between adjacent segments are measured via inductive edge-sensors. The personnel at NASA MSFC are performing a significant amount of testing in the area of controls/structure interactions; therefore, in addition to a description of the optical performance and aberration correction capability of the telescope, a description of the plan to model the mechanical structure with emphasis on how this will interact with the adaptive optics system is presented.
A hardware demonstration of segmented mirror systems for adaptive optics is described. The basis of the phased array mirror extendible large aperture (PAMELATM) concept is that large adaptive mirrors can be fabricated from many small segments by utilizing edge-sensors, which measure the piston error between segments. We have investigated the interaction between the piston and tilt control loops which direct the motion of individual segments. The segment tilt, which is set by a wavefront-sensor-based control loop, directly affects the piston error between segments; therefore, the segment piston control loop must be able to perform corrections much faster than the rate at which the tilt corrections are being performed. In this experiment, we have one fully actuated segment with a wavefront sensor measuring the error in the wavefront gradient. An adjacent segment is driven in piston to produce the piston error signal. We measure and present the bandwidth trade-offs between the two control loops and predict how this will affect the performance of larger systems. This interactive control loop methodology has an advantage over normal adaptive optics systems in that the computationally intensive wavefront reconstruction process can be removed due to the direct measurement of both the tilt and the piston errors.