Often measurement tasks occur, where specimens consist of multiple layers or topography shall be examined through contaminations. Especially for unknown layer materials, it is important to measure ...the layer's refractive index to compensate for the errors induced on the measurement of underlying surfaces. Chromatic Confocal Coherence Tomography is proposed as a new hybrid single-shot scheme for a simultaneous measurement of thickness and refractive index of semitransparent layers, combining chromatic confocal and interferometric information. As a proof of concept, first measurements are presented along with a short discussion about their uncertainties, where minimal layer thickness and resolution are dominated by the confocal part of the signal, that is mainly influenced by the chosen microscope objective.
One common way to measure asphere and freeform surfaces is the interferometric Null test, where a computer generated hologram (CGH) is placed in the object path of the interferometer. If undetected ...phase errors are present in the CGH, the measurement will show systematic errors. Therefore the absolute phase of this element has to be known. This phase is often calculated using scalar diffraction theory. In this paper we discuss the limitations of this theory for the prediction of the absolute phase generated by different implementations of CGH. Furthermore, for regions where scalar approximation is no longer valid, rigorous simulations are performed to identify phase sensitive structure parameters and evaluate fabrication tolerances for typical gratings.
Residual stress levels induced during the process are one of the more relevant characteristics of thermal spray coatings. Therefore, there are different techniques, such as the x-ray diffractometry ...or the classical micro hole drilling and milling method, to analyse and optimize the thermal spray coating process in order to obtain a desired level of residual stresses on coatings. The state of the art of the new developed non-contact, quasi non-destructive residual stress analysis method is presented. The material removal is based on laser ablation and complex ablation geometries are possible by using a spatial light modulator (SLM) for beam conditioning. 3D deformations on the specimen surface are measured in the nanoscale range by high-resolution digital holographic interferometry. Numerical procedures using the finite differences method are performed in order to calculate the shape geometry and the calibration curves required for the residual stress calculation from the measured 3D displacements, coating-substrate material combination and the ablation geometry. Experimental results on thermal spray coatings are presented and discussed with comparative measurements by the hole-drilling method. The potentials and difficulties of the method are discussed.
•Residual stress levels induced during the process are one of the more relevant characteristics of thermal spray coatings.•A very interesting and recently developed non-contact, quasi non-destructive residual stress analysis characterization technique for the analysis of residual stresses on coatings is presented.•The greatest attraction of this technique is the smart combination of the machining of complex geometries by a laser ablation process and the optical determination of superficial 3D deformations in the nanoscale range by high-resolution digital holographic interferometry.•Numerical procedures using the finite element method are performed in order to calculate the shape geometry and the calibration curves required for the residual stress calculation from the measured 3D displacements, coating-substrate material combination and the ablation geometry.
Digital shearography is an interferometric technique, which is often used for defect detection on composite structures. The measurement is fast and non‐destructive and thus suitable for the ...application to cultural heritage. However, a major drawback of the technique is the indirect measurement, because surface strain is used to detect subsurface defects. So the determination of depth, size, and type of the defects is rather difficult. To overcome this issue, we use a combination of finite element method simulation and shearographic measurement. Due to the comparison of both data sets, the inverse problem can be solved in a more reliable way. In this paper, we investigate the application of finite element method simulation for an improved defect detection on anisotropic material. We validate the technique on a wooden sample with notches on the backside.
An uncomplicated appendectomy in children is common. Safely minimizing the post-operative length of stay is desirable from hospital, patient, and parent perspectives. In response to an overly long ...mean length of stay following uncomplicated appendectomies in children of 2.5 days, we developed clinical pathways with the goal of safely reducing this time to 2.0 or fewer days. The project was conducted in an urban, academic children's hospital. The pathways emphasized the use of oral, non-narcotic pain medications; the education of parents and caregivers about expectations regarding pain control, oral food intake, and mobility; and the avoidance of routine post-operative antibiotic use. A convenience sample of 46 patients aged 3-16 years old was included to evaluate the safety and efficacy of the intervention. The mean post-operative length of stay was successfully reduced by 80% to 0.5 days without appreciable complications associated with earlier discharge. The hospital length of stay following an uncomplicated appendectomy in children may be successfully and safely reduced through the use of carefully devised, well-defined, well-disseminated clinical pathways.
High-performance objectives pose strict limitations on residual errors present in the system. External mechanical influences can induce structural vibrations in the optical system which causes a ...displacement of the lenses present in the system. This will influence the imaging performance, causing degraded images or broadened structures in a lithographic processes. In this paper an adaptive state observer for the detection of structural vibrations of the optical elements of an imaging system based on a series of wavefront tilt measurements is introduced. The observer output is used as an input for a closed-loop PD control to mitigate the lens displacements directly.
In this paper, we demonstrate how short temporal coherence digital holography with a femtosecond frequency comb laser source may be used for multi-level optical sectioning. The object shape is ...obtained by digitally reconstructing and processing a sequence of holograms recorded during stepwise shifting of a mirror in the reference arm. Experimental results are presented.
In this paper, a method for residual stress analysis of ceramic coatings by applying a laser for quasi non-destructive material removal and measuring the 3D displacement around the machined area by ...means of high-resolution digital holography is described. The residual stresses are retrieved by numerical calculations using the finite element method (FEM) from the measured 3D displacements, the profile of the machined hole and the material parameters of the coating and substrate. Experimental results on thermal spray coatings together with discussion of the difficulties, work in progress, potential of the method, and comparative measurements by the hole-drilling method are presented.
We report on first results obtained with two modified hologram optimization algorithms. These algorithms take into account the complex modulation characteristic of the spatial light modulators ...employed for hologram reconstruction. To this end the Jones matrices of the modulator as well as all other components of the setup are used within a modified direct binary search and an iterative Fourier transform algorithm. Geometrical phase effects are included in the optimization. Elimination of the analyzer behind the spatial light modulator is possible by that approach and for typical setups using twisted-nematic liquid crystal modulators an enhanced overall diffraction efficiency is achieved. Possible applications are the comparative digital holography and optical tweezers. Experimental results for the reconstructions of holograms with a Holoeye LC-R 3000 modulator are presented.
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