18 June 2007 Effect of broadband illumination on reconstruction error of phase retrieval in optical metrology
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Phase retrieval is a promising method for optical system and surface metrology that makes use of intensity measurements of diffraction patterns. An iterative algorithm is used to solve the inverse problem to find the phase of the field producing the measured intensity distributions. For practical reasons, such as the reduction of coherent artifacts or to improve the signal-to-noise ratio of the measured data, it is often desirable to measure intensity distributions using broadband illumination. It is possible to perform phase retrieval with broadband data by incorporating a broadband model of the system into the phase retrieval algorithm. To do this, the system is modeled at several discrete wavelengths and the results from each are summed incoherently to produce a broadband result. This significantly increases the computational load. We show here that when aberrations are small, accurate estimates of the OPD distribution, on the level of &lgr;/1000 RMS error, can be achieved using data with bandwidth up to about 10% as the input to a phase retrieval algorithm that assumes monochromatic data.
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Gregory R. Brady, Gregory R. Brady, James R. Fienup, James R. Fienup, "Effect of broadband illumination on reconstruction error of phase retrieval in optical metrology", Proc. SPIE 6617, Modeling Aspects in Optical Metrology, 66170I (18 June 2007); doi: 10.1117/12.726184; https://doi.org/10.1117/12.726184

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