Band-Pass and OH-Suppression Filters for the E-ELT - Design and Prototyping

Optical filters are used for a variety of purposes at astronomical telescopes. In the near infrared region, from 0.8 to 2.5 um, bandpass and edge filters are used to separate the different astronomical channels, such as the J, H, and K bands. However, in the same wavelength range light emission generated in the earth's atmosphere is superimposed on the stellar radiation. Therefore, ground based astronomical instruments measure, in addition to the stellar light, also unwanted contributions from the earth's atmosphere. The characteristic lines of this OH emission are extremely narrow and distributed over the complete NIR spectral range. The sensitivity of future telescopes, like the European Extreme Large Telescope (E-ELT) which is currently being designed by ESO, can be dramatically improved if the atmospheric emission lines are effectively suppressed while the stellar radiation is efficiently transferred to the detector systems. For this task, new types of optical filters have to be developed. In this framework new design concepts and algorithms must be used, combining the measurement needs with practical restrictions. Certainly, the selected deposition process plays the key role in the manufacturing process. Precise and highly stable deposition systems are necessary to realise such filter systems with an appropriate homogeneity. Moreover, the production control techniques must be adapted to match the high level of precision required in the NIR range. Finally, the characterisation set-ups for such filters systems have to be provided. The manufacturing of such a filter system for a feasibility study of an E-ELT instrument is presented. The design development, the deposition with adapted Ion Beam Sputtering deposition plants, and the characterisation of such filters in the J-Band is described.Comment: contribution to SPIE 8168 on 'Advances in Optical Thin Films IV', Marseille 201

Determination of the laser-induced damage threshold of polymer optical fibers

Investigating the properties of manufactured polymer optical fibers is essential to determine proper areas of application. Using pulsed laser radiation, especially with respect to laser activity in optical fibers, the maximum acceptable transmittable energy without inducing damage is of particular interest. Therefore, this work is related to laser-induced damage in polymer optical fibers at a wavelength of 532 nm and a pulse duration of 7.3 ns. In particular, the influence of the coupling condition on the transmittable pulse energy and the damage behavior applying an R-on-1 test procedure are analyzed in this study. The obtained results give information about the long-Term behavior and will be used to optimize the manufacturing process. © COPYRIGHT SPI

Laser-induced pit formation in UV-Antireflective coatings

Previous studies have shown that nanometer scale defects can lead to the formation of submicrometer craters, if located in coatings with a relatively small thickness. Due to the small size, such damages are challenging to detect in the online and offline damage detection and may therefore lead to an overestimation of the LIDT for the tested optical component. However, the influence of these nanopits on the optical properties and the impact on the initiation of catastrophic damage was not investigated in detail in the past. In order to study the correlation between nanopits, optical properties and catastrophic damage, samples with an AR-coating were fabricated by means of ion beam sputtering (IBS) and tested for their laser resistance by LIDT raster scans in the nanosecond regime at 355 nm. The generation and morphology changes of the nanopits were monitored for different pulse numbers and in dependence of the starting fluence. In addition to the inspection with an optical microscope in differential interference contrast (DIC) mode as prescribed by ISO 21254, alternative inspection methods, for example, dark field microscopy and scanning electron microscopy (SEM), were used to detect the nanopits. The damage test revealed that nanopits occur rarely in standard AR-coatings and possess only a small relevance for the LIDT. The typical damage morphology observed consisted of micrometer-sized pits which exhibited a stable size over a large fluence range and no growth after repeated irradiation. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only

Laser-induced degradation and damage morphology in polymer optical fibers

The radiation of pulsed laser systems can generate changes in various materials. On the one hand, these modifications can be used for a variety of applications i.e. laser welding, cutting and many more [1]. The precision and quality depends on the material and laser parameters. On the other hand, material changes are not always desired in other applications. When using optical materials such as optical fibers as a light guide or as a sensor, laser-induced damage effects inside the fiber are to be prevented to ensure constant light guidance and the reliable monitoring of a desired parameter. Therefore, investigations for quality assurance need to be performed. For this reason, this work investigates laserinduced damage in polymer optical fibers (POF) using a nanosecond pulsed laser system at a wavelength of 532 nm. The impact of different laser and fiber parameters on the long-term degradation behavior is observed. In addition, the overall degradation behavior as well as the knowledge gained by analyzing the damage morphology and distribution will be used to obtain a better understanding of the damage mechanisms

Miniaturized thin-film filters to connect multiple self-written waveguides

Self-written waveguides (SWWs) have been well investigated within the last decades. In most cases, they are used as low-loss coupling structures, i.e., to connect buried optical structures in photonic integrated circuits. In this work, we extend the field of possible applications for SWWs by embedding a novel thin-film filter to split the beam and connect multiple output ports simultaneously. The multilayer design of the dielectric filter can be customized to enable its application as a dichroic beamsplitter for photonic networks. The embedded thin-film filter was characterized in detail and used to connect an additional optical sensing element, which is also based on SWWs, to demonstrate its usability for measurement of physical quantities

Deposition and spectral performance of an inhomogeneous broadband wide-angular antireflective coating

The gradient index coatings and optical filters based on them are a challenge for fabrication. In a round-robin experiment basically the same hybrid antireflection coating for the visible spectral region has been deposited with three different techniques: electron beam evaporation, ion beam sputtering and radio frequency magnetron-sputtering. Spectral performances of such one-side and both-side coated samples have been compared with corresponding theoretical spectra of the designed profile. Also, reproducibility of each process is checked

Assessments for Mild Cognitive Impairment (MCI) and Functional Cognition: An Evidence-Based Practice Project

This Evidence-Based Practice (EBP) project addressed the following question: What occupational therapy and interdisciplinary assessments are currently used and have the best psychometric characteristics and are most effective for screening or evaluating functional cognition of individuals with mild cognitive impairment and measuring the outcomes of intervention programs for mild cognitive impairment

Dynamic liquefaction of shear zones in intact loess during simulated earthquake loading

The 2010-2011 Canterbury earthquake sequence in New Zealand exposed loess-mantled slopes in the area to very high levels of seismic excitation (locally measured as >2 g). Few loess slopes showed permanent local downslope deformation, and most of these showed only limited accumulated displacement. A series of innovative dynamic back pressured shear-box tests were undertaken on intact and remoulded loess samples collected from one of the recently active slopes replicating field conditions under different simplified horizontal seismic excitations. During each test, the strength reduction and excess pore water pressures generated were measured as the sample failed. Test results suggest that although dynamic liquefaction could have occurred, a key factor was likely to have been that the loess was largely unsaturated at the times of the large earthquake events. The failure of intact loess samples in the tests was complex and variable due to the highly variable geotechnical characteristics of the material. Some loess samples failed rapidly as a result of dynamic liquefaction as seismic excitation generated an increase in pore-water pressure, triggering rapid loss of strength and thus of shear resistance. Following initial failure, pore pressure dissipated with continued seismic excitation and the sample consolidated, resulting in partial shear-strength recovery. Once excess pore-water pressures had dissipated, deformation continued in a critical effective stress state with no further change in volume. Remoulded and weaker samples, however, did not liquefy, and instead immediately reduced in volume with an accompanying slower and more sustained increase in pore pressure as the sample consolidated. Thereafter excess pressures dissipated and deformation continued at a critical state. The complex behaviour explained why, despite exceptionally strong ground shaking, there was only limited displacement and lack of run-out: dynamic liquefaction was unlikely to occur in the freely draining slopes. Dynamic liquefaction however remained a plausible mechanism to explain loess failure in some of the low-angle toe slopes, where a permanent water table was present in the loess

Mechanical aspects in interferometric gravity wave detectors

In order to measure the tiny effects of gravitational waves, strains in space (i.e. relative changes in distance) of as little as 10-21 or even less have to be detected, at frequencies ranging from 10011z to several kHz. Large laser interferometers are the most promising approach to reach such extreme sensitivities. This lsquostraightforwardrsquo road is, however, obstructed by a multitude of effects that cause (or fake) such fluctuations in distance. Among these are seismic motions, thermal vibrations of optical components, pressure fluctuations of the residual gas in the vacuum tubes, and fundamental effects such as Heisenberg's uncertainty relation. What all of these noise sources have in common is that their effects can be reduced by the choice of sufficiently large arm lengths. This is what dictates the (very expensive) choice of arm lengths of 3 to 4 km in the currently proposed gravitational wave detectors (USA, D-GB, F-I, AUS, JAP)