We report on a method that can be used to improve the result of multiwavelength contouring in the case of objects with rough surface. It is based on the combined evaluation of multiple measurements with varying direction of illumination. While the individual measurements share the same systematics with respect to the shape of the investigated object, the noise arising from speckle decorrelation fluctuates statistically and hence can be reduced by means of averaging. For the case of three illumination directions we show that weighted averaging of the measured phase distributions enhances the signal-to-noise ratio by approximately 3 dB.
Fringe-resolved noncollinear autocorrelation extracts information about the pulse duration of ultrashort optical signals from analyzing the intensity envelope of fringes. By detecting nonlinear autocorrelation functions after frequency conversion, even an evaluation of temporal asymmetry and frequency chirp are enabled. Here we report on a modified approach based on replacing crossed plane waves by Bessel-like beams. In comparison to the conventional method, appropriate mathematical transforms have to be applied. The method is simple and single-shot capable and takes advantage of specific advantages of pseudo-nondiffracting beams. First proof-of-principle experiments with fewfemtosecond pulse durations were performed and compared to simulations. In multishot operation regime, the implementation of phase-shifting procedures by spatial light modulators promises considerable improvements of the time resolution analogous to the known principle of phase-shift interferometry.
We propose a new application of broad band lasers for digital holography. The aim is to capture the shape of objects by a single hologram using multiple wavelengths. Our approach is to separate the reference wave spectrally by a grating while the object wave remains unaffected. This leads to many lamellar holograms in one hologram. As consequence different restrictions like aperture and wavelength dependency of the reconstruction algorithm have to be taken into account. In experiments we have successfully demonstrate that lamellar holograms can be generated, reconstructed and that all necessary steps for shape measurement are accomplishable.
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