JEOS:RP - Journal of the European Optical Society Rapid publications
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Ultra-wide angle lens design with relative illumination analysis
Full text linkAn ultra-wide angle lens design with relative illumination analysis is presented. The half field angle of 80°, the relative illumination of the image plane will be reduced. It is necessary to increase the image numerical aperture ratio for X and Y direction, and decrease the angle between the chief ray and optical axis in the image space. However the ultra-wide angle lens induces great barrel distortion causing image extrusion. Therefore, we use F-theta distortion to replace optical distortion. Seven lenses and two pieces of flat glass are used for a sensor 1/6†sensor with 2.1 million pixels. The final result for the lens is a half viewing angle of 80°, F/2.4, a focal length 1.1 mm, a length of 22.37 mm, F-theta distortion of less than 2%, and relative illumination greater than 83%
Simulation of mid-spatials from the grinding process
Full text linkThis paper focuses on the simulation of the creation of mid-spatial frequencies (mid-spatials) during the grinding process of optical components. The goal is to simulate this generation process and determine the correlating grinding parameters for mid-spatials. On this base, grinding parameters which lead to less mid-spatials could be determined
A novel method of measuring upwelling radiance in the hydrographic sub-hull
Full text linkIn this study we present a new method useful in collecting upwelling radiance (Lu) from a platform submerged in a hydrographic sub-hull or moon pool of a research vessel. The information analyzed here was obtained during a field campaign in the Northwestern European shelf seas aboard the new research vessel SONNE. As the platform was located at the center of the ship, there is minimal effect from pitch and roll which is known to influence upwelling radiance observations. A comparison of the measurements from this platform with a free falling hyperspectral profiler was performed to determine the degree of uncertainty that results from ship shadow. For given Lu(λ) in situ data we observed ±33% intensity deviations compared to profiling measurements that can be attributed to instrument shading during moon pool installation and environmental perturbations. Furthermore Lu(λ) in situ spectra variations were observed at lower wavelengths, therefore a form fitting algorithm was adapted to receive corresponding depths with identical spectral form from Lu(z, λ) profiler casts. During an east to west transect in North Sea with a schedule speed up to 12 knots in situ radiance reflectance rrs(7, λ) measurements at 7 meter depth were performed with this novel radiometer setup. In spite of any restrictions originating from the sub-hull installation, water masses mixing zone from CDOM dominated coastal waters in the Skagerrak Strait towards the open North Sea were successfully derived thus offering an underway applicable upwelling radiance sensing not suffering from sun glint or other typical restrictions of above water radiometer installations
Polishing material removal correlation on PMMA – FEM simulation
Full text linkThe complexity of polishing is very high and experience in this field is required to achieve reproducible deterministic results concerning shape accuracy. The goal of this work is to predict the material removal of the polishing process on PMMA (Polymethylmethacrylate) using an industrial robot polisher. In order to predict the material removal, a FEM Model was created representing the polishing process. This model will help to predict the material removal when polishing parameters are changed. Experiments were carried out and compared to the results obtained from the different parameters tested in the simulation
Statistical classification of soft solder alloys by laser-induced breakdown spectroscopy: review of methods
Full text linkThis paper reviews machine-learning methods that are nowadays the most frequently used for the supervised classification of spectral signals in laser-induced breakdown spectroscopy (LIBS). We analyze and compare various statistical classification methods, such as linear discriminant analysis (LDA), quadratic discriminant analysis (QDA), partial least-squares discriminant analysis (PLS-DA), soft independent modeling of class analogy (SIMCA), support vector machine (SVM), naive Bayes method, probabilistic neural networks (PNN), and K-nearest neighbor (KNN) method. The theoretical considerations are supported with experiments conducted for real soft-solder-alloy spectra obtained using LIBS. We consider two decision problems: binary and multiclass classification. The former is used to distinguish overheated soft solders from their normal versions. The latter aims to assign a testing sample to a given group of materials. The measurements are obtained for several laser-energy values, projection masks, and numbers of laser shots. Using cross-validation, we evaluate the above classification methods in terms of their usefulness in solving both classification problems
Optimum Apodization Profile for Chirped Fiber Bragg Gratings based Chromatic Dispersion Compensator
No full textIn this paper, we optimize the apodization profile to improve the dispersion compensation performance of the chirped fiber Bragg gratings (CFBGs). Tanh, Exponential, and Hamming apodization profiles were evaluated at 2000 nm wavelength. Our aim is to obtain the minimum average group delay ripple (GDR) and maximum FWHM bandwidth. The result shows that the best FWHM bandwidth is obtained by using Tanh profile that is approximately 96.27%. No significant difference can be observed in the GDR
Polarization beating of random electromagnetic beams
Full text linkWe consider temporal interference of two stationary, quasi-monochromatic, partially polarized optical beams with different mean frequencies. We show that both the intensity and the polarization state, represented by the Stokes parameters, exhibit beating, i.e., periodic temporal variation with frequency specified by the difference of the mean frequencies. The contrasts, or visibilities, of the Stokes-parameter changes are characterized by the equal-time electromagnetic degree of coherence between the beams. If the beams are otherwise identical random processes, but with spectra centered at different frequencies, then the polarization modulation is characterized by the degree of polarization, consistently with a recent interferometric interpretation of this quantity. Our results provide insight into the role of polarization in beating of electromagnetic waves
New freeform manufacturing chains based on atmospheric plasma jet machining
Full text linkNew manufacturing chains for precise fabrication of asphere and freeform optical surfaces including atmospheric Plasma Jet Machining (PJM) technology will be presented. PJM is based on deterministic plasma-assisted material removal. It has the potential for flexible and cost-efficient shape generation and correction of small and medium-sized optical freeform elements. The paper discusses the interactions between the plasma tools and optical fused silica samples in the context of the pre-machined and intermediate surface states and identifies several plasma jet machining methods for freeform generation, surface correction, and finishing as well as suitable auxiliary polishing methods. The successful application of either processing chain is demonstrated
Controlling the optical creation of gold nanoparticles in a PVA matrix by direct laser writing
Full text linkWe report about the study on the physical features of gold nano-particles (GNPs) created by 2-photons photo-reduction Direct Laser Writing in a Poly-Vinyl Alcohol (PVA) matrix doped with HAuCl4. We drop cast a film of the PVA+ HAuCl4 onto a glass substrate, in which we create 1D gratings made by stripes of GNPs with a single laser sweep. We show that the stripe width increases with the laser power and the exposure time. We also analyse the influence of the exposure time over the created nano-particles size distribution and density and we show that by suitably adjusting the exposure time it is possible to maximize the frequency of a given diameter. By comparing the experimental results with a polymerization “voxel†model, we are able to evaluate the effective cross section for 2- photons absorption of our material
Robotic automation in computer controlled polishing
Full text linkWe first present a Case Study – the manufacture of 1.4 m prototype mirror-segments for the European Extremely Large Telescope, undertaken by the National Facility for Ultra Precision Surfaces, at the OpTIC facility operated by Glyndwr University. Scale-up to serial-manufacture demands delivery of a 1.4 m off-axis aspheric hexagonal segment with surface precision < 10 nm RMS every four days, compared with a typical year or more for an one-off part. This requires a radically-new approach to large optics fabrication, which will inevitably propagate into wider industrial optics. We report on how these ambitious requirements have stimulated an investigation into the synergy between robots and computer numerically controlled (‘CNC’) polishing machines for optical fabrication. The objective was not to assess which is superior. Rather, it was to understand for the first time their complementary properties, leading us to operate them together as a unit, integrated in hardware and software. Three key areas are reported. First is the novel use of robots to automate currently-manual operations on CNC polishing machines, to improve work-throughput, mitigate risk of damage to parts, and reduce dependence on highly-skilled staff. Second is the use of robots to pre-process surfaces prior to CNC polishing, to reduce total process time. The third draws the threads together, describing our vision of the automated manufacturing cell, where the operator interacts at cell rather than machine level. This promises to deliver a step-change in end-to-end manufacturing times and costs, compared with either platform used on its own or, indeed, the state-of-the-art used elsewhere