Accession Number:

ADA030055

Title:

COAT/Target-Signature Interactions

Descriptive Note:

Final technical rept. 1 Aug 1975-1 Feb 1976

Corporate Author:

HUGHES RESEARCH LABS MALIBU CA

Report Date:

1976-07-01

Pagination or Media Count:

92.0

Abstract:

Amplitude modulation effects which can occur when target return speckle patterns move by a receiver aperture, have been studied in adaptive optical systems that use multidither coherent optical adaptive techniques COAT . Good agreement is found between experiemental, analytical, and computer simulation studies made to characterize the degree to which COAT systems can be affected by speckle. Both experimental and computer simulation results show that in the worst-case, the convergence-level Strehl ratio of an 18-element COAT system is reduced to 30 of that obtained with no spurious speckle modulations. Calculations using an analysis developed here, predict an average covergence level of 0.18, in reasonable agreement with experiment, but somewhat pessimistic. In the presence of speckle noise, the COAT system convergence rate is unaffected as is the convergence level until it reaches the average level that is set by the speckle noise. The convergence level then oscillates in a random fashion between well-defined maximum and minimum vaules. For any given multidither COAT system, we have developed analytical and computer simulation tools that can accurately predict the average convergence level and oscillation extremes once the power spectrum of speckle-induced modulations is known. We have observed that reducing the servo gain bandwidth reduces the effect of speckle modulations nearly to zero, but at the cost of increased convergence time.

Subject Categories:

  • Lasers and Masers
  • Optics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE