Final Report Summary - RIBLET SENSOR (Light Scattering on Micro Structured Surface Coatings) Executive Summary: With the application of appropriate surface structuring on aircrafts, up to 8\% fuel may be saved in regular air traffic.This not only decreases costs, but especially reduces exhaust of greenhouse gases significantly.Before these techniques can be introduced into productive environments, a controlling method for the quality of surface structuring had to be established to be used during fabrication and service, ensuring persistent quality of the structured coatings and a justified decision for surface renewal.In this project, these important requirements for achieving the improvements defined above are fulfilled.We have shown that fast sampling is possible using noncontacting laser probing, and we have presented a working preliminary configuration for the sensor.In the theoretical part, a model for the interaction between a probing laser beam and the surface is developed and the resulting wavefront is derived. This is done using a combination of Huygens-Fresnel diffraction theory and geometrical optics. The model is then used to counsel the design of the experimental setup, to interpret the emerging data and to develop characteristic quantities for the sample, their derivation from the data and their signal-to-noise ratio.In the experimental part, the interaction of laser light with the structured riblet surface is studied. For this purpose an optical setup was installed to perform measurements of undegraded and degraded surfaces depending on a variety of experimental parameter like probe wavelength or angle of incidence.The results of these measurements in the form of intensity distributions as a function of angles are constantly compared and checked with the theoretical calculations. A preliminary configuration of an optical setup with an optimized laser system is now available for further studies.It allows for very sensitive measurements of even slight degradations of the surfaces.Here, it is regardless if the damage to the riblets is symmetrical or asymmetrical due to mechanical loss of material or if it is deriving from changes of reflectivity due to chemical processes of the riblet material itself.A fast implementation in commercial products should be possible on the basis of this report. Project Context and Objectives:The interaction of light with micro- and nanostructured dielectrics strongly attracts researcher's interest in the field of (nonlinear) optics and photonics in recent years. This interest is particularly driven by the rapid success and the tremendous technical improvements in the fabrication of micro- and nanostructured materials using for instance EUV-photolithography, optical micropatterning with fs-laserpulses and e-beam writing. It enabled the fabrication of structures with spatial variation of the susceptibility on a scale far below the light wavelength, i.e. with a spatial precision on the nanometer scale. At the same time, the fabrication of three-dimensional, spatially structured dielectrics was introduced. Applying these technologies for photonic industries, the targeted design of optical components with given features has become possible.The impact of the scientific research in light-matter interaction and the outcome of the various research activities becomes apparent regarding the variety of novel technologies that were particularly developed for the field of photonics and that are already established on the market: photonic crystals and photonic crystal fibers, next-generation integrated optical components (lasers and filters in silica chips), Bragg-filters for small-bandwidth laser systems, DWDMs for telecommunication purposes or dielectrics with periodically-poled nonlinearities for frequency conversion.We note that in any of these systems, periodic and aperiodic structures as well as structures with defects or phase-jumps are at the origin of the functionality. For instance, chirped mirrors for the optimization of fs-laser cavities, are built from intelligently structured dielectric layers and allow for a reflectivity in a broad wavelength regime with flat-top profile and wavelength-dependent phase shift.It is this most-recent state-of the art knowledge on light-matter interactions with micro- and nanostructured dielectrics that has been the starting point and base for our outmost innovative project approach.According to the overall task, microstructured surfaces that particularly show aging effects of their structure on the sub-$\mu$m scale were inspected by a simple optical system.We have solved this task by combining the analysis of diffraction features and properties based on geometrical optics emerging from the interaction of the structured surface under study with plain electromagnetic waves as sketched in figure 1.We have solved this task by using a controlled electric-field coupling of counterpropagating electromagnetic waves that interact with the structured surface under study. The principle scheme underlying the sensor development is sketched in figure 1.The resulting setup can easily be transferred to a low-cost, low-weight, hand-held or robot-driven optical system with low power consumption but high precision using state-of-the-art semiconductor laser systems in the near-infrared spectral range.In comparison to other surface sensitive methods, such as low-coherence microscopy or reflectometry, our approach further allows a rapid scan of the surface, i.e. it allows for short-time structural inspection on the ms-time scale that is advantageous in view of scanning large surface areas and/or repetitive measurements of surface regimes in order to increase the signal-to-noise ratio. The large parameter set enables further amilioration of the signal-to-noise ratio. Further, we gain a more detailed insight to riblet degradation that is originating from particle deposition such as dust inclusions. Potential Impact: As described in the abstract, the the sensor whose preliminary configuration is presented in this report is of crucial importance for the application of structured coatings on airplane surfaces.These coatings may have significant impact on the fuel consumption in commercial air traffic, which can not only reduce cost but also considerably decreases exhaust of greenhouse gases.Apart from these ecological aspects, the sensor itself and the connected coating carry economic potential by creating jobs in the European Union and contributing to the European exports in the high-tech field.Having presented the preliminary configuration, as a next step the device has to be developed towards a commercial device.Consequently, it has to be produced in bulk quantities and distributed in and outside the EU.Regarding the coating instruments for the application have to be manufactured and it has to be applied on parts of the airplane.These requirements make room for several start-up companies and a considerable amount of jobs.Additionally, existing European airplane manufacturers gain market advantages by applying the techniques developed in this project.Finally, users in both ground and air crews have to be instructed in the maintenance procedures, creating additional jobs in this sector. List of Websites:http://www.imlau.physik.uni-osnabrueck.deContact Details:Mirco Imlau, PhDProfessor for Experimental PhysicsUniversity of Osnabrueck, Department of PhysicsBarbarastraße 7 / building 32, room 12949076 OsnabrückGermanyPhone +49 541 969 2654Secretary +49 541 969 3344 (Mrs. Gabriel)Fax +49 541 969 3510E-mail: mirco.imlau@uni-osnabrueck.de Related documents final1-publishable-summary.pdf
