Spectral and temporal phase evaluation for interferometry and speckle applications

Interferometry using a single wavelength delivers the surface topography and surface heights of optically polished surfaces. However, discrete steps and holes cannot be determined, the sensitivity is fixed, and the analysis of optically rough surfaces is not possible. Some of these limitations can be overcome by using two or more wavelengths. In wavelength scanning interferometry, the frequency of the modulation induced by the wavelength change is determined independently for each image pixel. The tuning range determines the resolution of measurements, while the tuning step limits the range of the measurements. Laser diodes can be tuned, but an external cavity is needed for a larger mode hop free wavelength variation. Polished and optically rough surfaces can be analyzed in the same manner. In a new development, the application of temporal evaluation of speckles for deformation and shape measurement will be discussed. It turns out that spectral and temporal phase analysis can be very useful for many applications in optical metrology. Experimental results will support the methods discussed.

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