Phase Diversity Wavefront Sensing for Control of Space Based Adaptive Optics Systems

Phase Diversity Wavefront Sensing (PD WFS) is a wavefront reconstruction technique used in adaptive optics, which takes advantage of the curvature conjugating analog physical properties of a deformable mirror (MMDM or Bi-morph) such that the computational intensity required for correcting an aberrated wavefront, becomes simplified over traditional Shack-Hartmann WFS techniques. By looking at an image reflected off a deformable mirror by two cameras placed on either side of focus of a lens, intensity differences, indicating wavefront aberration in the beam, can be detected by the cameras acting together as a WFS and analyzed by a computer providing control to the actuators of a deformable mirror such that any detected difference in intensities between the two cameras can be minimized. This process of mirror surface conjugation serves to correct for the aberrated or curved wavefront by reflecting a new wavefront, compensated for curvature, such that its reflection is approximately planar. The theory of PD WFS is well documented however, there is very little quantifiable information regarding the specific challenges in designing a functioning PD WFS. In this research a PD WFS was designed and the concept proven such that a wavefront could be corrected through a computer controlled closed loop conjugation of a deformable mirror. The results were analyzed using a traditional Shack-Hartmann WFS and off-the-shelf Front Surfer wavefront analysis software to verify the validity of the experimental data. PD WFS has become critical in the development of segmented mirror adaptive optical systems where traditional wavefront reconstruction using Shack-Hartmann wavefront sensing tends to break down at the mirror segment edges. The Naval Postgraduate School, Spacecraft Research and Design Center (SRDC) intends to explore the use of a segmented mirror adaptive optical systems for space based applications.