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Digital speckle pattern interferometry (DSPI) has been widely used for surface metrology of optically rough surfaces. Single visible wavelength can provide high measurement accuracy, but it limits the deformation measurement range of the interferometer. Also, it is difficult to reveal the shape of a rough surface with one wavelength in normal illumination and observation geometry. Using more than one visible wavelength in DSPI, one can measure large deformations as well as shape using synthetic wavelength approach. In this work, we will discuss multi-wavelength speckle pattern interferometry using a Bayer RGB sensor. The colour sensor allows simultaneous acquisition of speckle patterns at different wavelengths. The colour images acquired using RGB sensor is split in to its individual components and corresponding interference phase map is recovered using error compensating phase shifting algorithm. The wrapped phase is unwrapped to quantify the deformation or shape information of the sample under inspection. Theoretical background of RGB interferometry for deformation and shape measurements, and experimental results will be presented. Ministry of Education (MOE) National Medical Research Council (NMRC) Accepted version The authors would like to acknowledge the financial support from the Singapore Ministry of Health’s National Medical Research Council (NMRC/OFIRG/0005/2016: M4062012) and Tier 1 grant funded by Ministry of Education Singapore (RG144/18: M4012098).

If the appropriate phase and/or amplitude profile is placed on a Diffractive Optical Element (DOE) it can practically generate an image of an object (hologram) by diffraction of the light. The problem of generating computer holograms consists of calculating numerically the profile of phase and/or amplitude with which the DOE should be built. Computer Generated Holograms (CGH) can be used to construct general-purpose optical elements in the sense that they serve to transform a spatial distribution of light into any other. In this way, they are used in optical communication systems, laser machining, laser welding, optical readers, human vision, data storage and visualization, image processing, among others. Unlike the optical techniques for generating holograms, in the CGH both the desired image and the phase and/or amplitude distribution are calculated numerically. In this work, a web environment application has been developed to calculate the phase changes that a coherent beam of light must undergo when incident on a DOE, so that it is transformed by Fraunhofer diffraction, in the hologram of an object. We use an algorithm with iterative Fourier transformations (IFTA) that uses regulation and stabilization parameters can be chosen by the user. In addition, the user has the freedom to choose holograms for optical applications (free of speckles) generating initial diffusers of a limited band and without phase singularities. © Springer Nature Switzerland AG 2018.

We propose a method for calculating appropriate α-band limited diffusers using the fractional Fourier transform. In order to do this, we implement a method for performing a numerical interpolation in the fractional Fourier domain. Such diffusers with compact support in the Fresnel regime may be used in fractional Fourier optical systems where the use of diffusers produce speckles, e.g. digital holography or optical encryption. Numerical simulations are presented. © 2016 SPIE. Brussels Photonics Team (B-PHOT);Research Foundation Flanders;The Society of Photo-Optical Instrumentation Engineers (SPIE);Visit Brussels

This article will give an overview of all effects that determine the spectral features amplitude (SFA). The origin of spectral features is explained and methods are indicated that can be used to minimize the SFA. Spectral features are observed in the ratio between two spectra of sun calibration measurements. Mechanisms helping to reduce spectral features are spectral averaging, angular averaging, and temporal averaging. It will be shown what optical design choices can be made in order to benefit from these SFA reducing mechanisms. In the final chapter some insight in the modeling is given where four types of diffusers are compared. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

The possibility of using temporal analysis to find the relation between chromatic properties of probe radiation and coherent properties of the optical images of rough non-planar objects is substantiated. The analysis is based on the use of the time correlation function and on the study of the speckle pattern contrast in the optical images. The conditions are determined under which the different parts of the optical image of an object are coherent, partially coherent and incoherent, while probe radiation is manifested as monochromatic, quasi-monochromatic, and polychromatic. It is shown that these conditions depend considerably on the object surface shape. The use of the temporal analysis for three-dimensional imaging of an object by its planar images and improving the optical image quality by removing its speckle pattern is illustrated by examples.

Spectral features are introduced by the diffuser that is used during on-board sun calibration. New findings are presented on how to reduce the size of these spectral features. Reduction can be obtained via optical design of the calibration unit, but also in creating a better diffuser. A novel diffuser design will be presented and its performance will be compared to standard diffusers like an Aluminum diffuser, a Spectralon diffuser, and the QVD (Quasi Volume Diffuser). For the in-house spectral features testing setup an improvement of about a factor of eight was obtained for the new diffuser type when compared to QVD. QVD in its turn is already better than an Aluminum diffuser by a factor of ten. Spectralon and QVD are found to be about equally good when measured in terms of spectral features reduction. The novel diffuser is referred to as SanDiff since it is a sandwich of QVD and PTFE material. For the SanDiff also the BSDF was measured and will be presented here. © 2009 SPIE.

We report on a theoretical/experimental model to predict the depth sensitivity of laser Doppler perfusion imager. Further more we show the quantitative influence of speckles on laser Doppler perfusion imager response to scattering at different depths. The model is based on Monte Carlo simulations and experiments on static and dynamic scattering phantoms made of polystyrene microspehers. The experimental results are in good agreement with our theoretical predictions. The results show that the depth sensitivity of the laser Doppler perfusion imager is influenced by the speckles. The effects are big, especially when a narrow beam is used for measurement. We propose that a correction method should be developed based on speckle size in order to have a reliable blood perfusion information independent of tissue optical properties.

The methodology of objective assessment, which defines image quality in terms of the performance of specific observers on specific tasks of interest, is extended to temporal sequences of images with random point spread functions and applied to adaptive imaging in astronomy. The tasks considered include both detection and estimation, and the observers are the optimal linear discriminant (Hotelling observer) and the optimal linear estimator (Wiener). A general theory of first- and second-order spatiotemporal statistics in adaptive optics is developed. It is shown that the covariance matrix can be rigorously decomposed into three terms representing the effect of measurement noise, random point spread function, and random nature of the astronomical scene. Figures of merit are developed, and computational methods are discussed.

We show that speckles play an important role in laser Doppler perfusion imaging. The influence of speckles on the signal amplitude and the Doppler spectrum is demonstrated experimentally on particle suspensions with different scattering levels and varying beam width. Polystyrene microsphere suspensions with known optical properties are used to make scattering samples. A theoretical model is explained to calculate the speckle size from the back scattered intensity distributions. The coherence area is calculated with Monte Carlo simulations on different scattering samples and experiments are performed to validate our theoretical model. The experimental results are in good agreement with our theoretical predictions.

We show that the time evolution of near-field scattering speckles, originated by a fluid suspension of particles, provides information about the velocity field in the fluid. This information can be extracted from a statistical analysis of speckle fields taken at different times, either by measuring their cross-correlation function or by recovering the power spectrum corresponding to the difference between the two speckle fields. Experimental data are in accordance to the expected behaviors. The results are independent of the scatterer's size, allowing one to exploit the technique also with sub-wavelength tracking particles.

We propose a simple measurement setup in reflection and a movement evaluation procedure based on a two dimensional recording of subjective speckle images. Averaging of cross correlation functions is used to determine translations. We show experimentally a 10 nm precision on a 50 µm measurement range with respect to systematical errors. An image library is shown to extend the range of measurements. Limitations are given and documented improvements are predicted to result in accuracy better than 5 nm over a range of 150 µm.