A method of wavefront sensing (more precisely characterized as a method of determining the deviation of a wavefront from a nominal figure) has been invented as an improved means of assessing the performance of an optical system as affected by such imperfections as misalignments, design errors, and fabrication errors. Unlike some prior methods, this method does not require the use of an expensive, complex interferometric instrument for testing the optical system of interest: indeed, if the system under test includes an image sensor at its focal plane, then this method does not require any optical instrumentation other than the optical system under test. Unlike some other prior methods, this method does not involve processing of multiple defocused images by a nonlinear iterative phase-retrieval algorithm and interpretation of results by a human expert in phase retrieval. Instead, this method involves a single non-iterative algorithm that solves for the wavefront from a single in-focus image, without need for interpretation of results. Hence, the main advantages of this method over the prior methods are reduced computing time and reduced labor.

At the time of writing this article, only fragmentary information about the method is available. Beyond what has been stated above, what is known is the following:

  • The method is implemented by software running on a single-processor computer that is connected, via a suitable interface, to the image sensor (typically, a charge-coupled device) in the system under test.
  • The software collects a digitized single image from the image sensor.
  • The image is displayed on a computer monitor.
  • The software directly solves for the wavefront in a time interval of a fraction of a second.
  • A picture of the wavefront is displayed.
  • The solution process involves, among other things, fast Fourier transforms. It has been reported to the effect that some measure of the wavefront is decomposed into modes of the optical system under test, but it has not been reported whether this decomposition is postprocessing of the solution or part of the solution process.

This work was done by Richard G. Lyon of Goddard Space Flight Center. GSC-15208-1

NASA Tech Briefs Magazine

This article first appeared in the April, 2009 issue of NASA Tech Briefs Magazine.

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