Scintillation Control for Adaptive Optical Sensors

Abstract

Public Reporting burden for this collection of information is estimated to average 1 hour per response, including the time and maintaining the data needed, and completing and reviewing the collection of information. Send comment regarding information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for infom 1204, Arlington, VA 22202-4302, and Michigan Technological University (MTU) has been investigating strategies for overcoming the effects of scintillation on adaptive optical imaging and laser beam projection systems which must operate in the presence of extended path turbulence. The approach originally proposed under this contract involved using two deformable mirrors to fully conjugate the received or transmitted beam. Our investigations into this concept have shown that implementation details associated with the use of real adaptive optical hardware will likely limit the effectiveness of the two deformable mirror technique. As a consequence, an alternative approach using one deformable mirror was developed, and its performance was investigated. This technique exploits the fact that, under strong scintillation conditions, information about the phase of the beacon field is incorporated in the intensity of the beacon field. Hence, deformable mirror commands which are consistent with all of the intensity measurements available to an adaptive optical system are processed using a new nonlinear optimization-based algorithm. Our studies of the performance of this technique have shown that under conditions of saturated scintillation this new approach significantly outperforms the standard centroid-based processing of the Hartmann sensor measurements. An experiment conducted at MTU has demonstrated the ability to predict a laser intensity pattern in a distant target plane using Hartmann sensor measurements of the field reflected from a deformable mirror. One accepted journal article, and one submitted journal article have resulted from this work, along with three conference papers. In addition, this work forms the basis of a program which is now being conducted with the Airborne Laser Technology Division. that implementation details associated with the use of real adaptive optical hardware will likely limit the effectiveness of the two deformable mirror technique. As a consequence, an alternative approach using one deformable mirror was developed, and its performance was investigated. This technique exploits the fact that, under strong scintillation conditions, information about the phase of the beacon field is incorporated in the intensity of the beacon field. Hence, deformable mirror commands which are consistent with all of the intensity measurements available to an adaptive optical system are processed using a new nonlinear optimization-based algorithm. Our studies of the performance of this technique have shown that under conditions of saturated scintillation this new approach significantly outperforms the standard centroid-based processing of the Hartmann sen...