Enhancement of third harmonic generation induced by surface lattice resonances in plasmonic metasurfaces

We investigate experimentally Third Harmonic Generation (THG) from plasmonic metasurfaces consisting of two-dimensional rectangular lattices of centrosymmetric gold nano-bars. By varying the incidence angle and the lattice period, we show how Surface Lattice Resonances (SLRs) at the involved wavelengths are the major contributors in determining the magnitude of the nonlinear effects. A further boost on THG is observed when we excite together more than one SLR, either at the same or at different frequencies. When such multiple resonances take place, interesting phenomena are observed, such as maximum THG enhancement for counter-propagating surface waves along the metasurface, and cascading effect emulating a third-order nonlinearity.Comment: 6 pages, 5 figures, accepted in Optics Letters-Optic

Optical properties of black silicon structures ALD-coated with Al 2 O 3

Atomic layer deposited (ALD) Al 2 O 3 coatings were applied on black silicon (b-Si) structures. The coated nanostructures were investigated regarding their reflective and transmissive behaviour. For a systematic study of the influence of the Al 2 O 3 coating, ALD coatings with a varying layer thickness were deposited on three b-Si structures with different morphologies. With a scanning electron microscope the morphological evolution of the coating process on the structures was examined. The optical characteristics of the different structures were investigated by spectral transmission and reflection measurements. The usability of the structures for highly efficient absorbers and antireflection (AR) functionalities in the different spectral regions is discussed

High precision electron-beam-lithography for optical high performance applications

Due to its high resolution end flexibility, electron beam lithography (EBL) became an essential fabrication technique for micro-optical elements that are used in high performance applications. Nevertheless, the sequential writing strategy used in EBL enforces a stitching approach in order to fabricate large area micro-optical elements. Inherently, the stitching of special subareas leads to inaccuracies in the optical function of the fabricated micro-optics, which usually appears as stray light. In this paper we report about a method to calibrate the stitching process and to reduce the stray light artefacts, respectively. The optimization method is based on the evaluation of angle resolved stray light measurements of special test gratings. In particular, the optimization concerns about spurious stray light peaks, also known as “Rowland ghosts”. In a first step, the qualitative and quantitative characteristics of the observed Rowland ghosts are investigated in a theoretical model in order to deduce the modality of the stitching inaccuracy and the strength of the alignment error. In a second step, the calibration of the subarea-stitching is demonstrated on the example of a contemporary spectrometer grating. It is shown that the Rowland ghosts can be reduced significantly and the stitching process can be controlled in the nm-range

Nano-optical quarter-wave plates for applications in the visible wavelength regime: fabrication, tolerances and in-situ process control

The controlling of the polarization state of light is required for various photonic applications, e.g. for biomedical imaging, lithography, microscopy or ellipsometry. Major advantages ofmicro- and nanostructures for polarization control are realization of elements for spectralbands, where no alternatives exist (e.g. polarizers in the UV wavelength range) and betterintegration with optical elements or sensors. Nano-optical polarizers and wave plates can beused to fully manipulate and convert the state of polarization. The fabrication of sub-wavelength grating quarter-wave plates for applications in the visible and near infraredwavelength regime is challenging. In this work major grating structure deviations, namelygrating ridge tilt, chamfers on top of the ridges, grating displacement and their influence onphase retardation are investigated. Basing on this we present theoretical investigations andexperimental results for an in-situ process control. Thereby, the impact of structure deviationscan be compensated and a fine tuning of the phase retardation becomes feasible. Wedemonstrate this approach by fabrication of a wave plate for 532nm wavelength. This work isthe foundation for future development of such an in-situ process control

Surface relief gratings manufactured by lithographic means being a candidate for VLT MOONS instrument's main dispersers

Surface relief gratings are well-established elements for high power laser applications, e.g. ultra-short pulse compression. A binary submicron period profile, realized by e-beam lithography and reactive ion beam etching in a dielectric material, is utilized for nearly one-hundred percent diffraction efficiency. Because these gratings are manufactured without any replication techniques, a high wave front accuracy and a low stray light background can be achieved. Spectroscopic applications require additional properties, i.e. a larger spectral bandwidth and Off-Littrow operation. We present new approaches for surface relief gratings realized either via multi-level staircase profiles or exploiting sub-wavelength features. The RVS spectrometer grating in ESA's GAIA mission is a prominent example where these techniques are already in use. The current contribution focuses on the results achieved during a pre-development performed for the MOONS instrument intended to operate at VLT

Modeling electro-optical characteristics of broad area semiconductor lasers based on a quasi-stationary multimode analysis

To increase the brightness of broad area laser diodes, it is necessary to tailor the optical properties of their waveguide region. For this purpose, there is the need for simulation tools which can predict the optical properties of the complete device and thus of the outcoupled light. In the present publication, we show a numerical method to calculate typical intensity distributions of the multimode beam inside a high-power semiconductor laser. The model considers effects of mode competition and the influence of the gain medium on the optical field. Simulation results show a good agreement with near and far field measurements of the analyzed broad area laser diodes

Design, analysis and fabrication of refractive beam shaping elements for optical storage applications

For the next generation of DVD we have designed an "asymmetric Gaussian to flat-top" converter which uses two refractive optical elements. The design method is based on conservation of energy. This approach leads to an analytically numerical nonparaxial wave-propagation as well as by experimental characterization. In detail, we have studied the tolerance to phase noise, the tolerance to deviations from the specified form and the tolerance to positioning errors. We observed, that the flat-top-intensity shows a very height sensitivity to phase noise. The sensitivity is increased by the intensity distribution in the focal plane of the high NA-focusing lens are investigated. First experimental results of a shaping element fabricated by direct write in resist are presented