JEOS:RP - Journal of the European Optical Society Rapid publications
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Eigenvalue calibration methods for polarimetry
Get PDFComplex polarisation sensitive systems such as imaging Mueller matrix polarimeters are commonly calibrated using the eigenvalue calibration method. In this paper we present an extensive review of the method and an existing variant. We also introduce two more variants of the method to calibrate imaging polarimeters that use high numerical aperture optics. The calibration methods are tested using a Mueller matrix confocal microscope of high numerical aperture, and the effect of the pinhole size on the polarisation is also assessed experimentally
Lossless polarization attraction simulation with a novel and simple counterpropagation algorithm for optical signals
Get PDFWe introduce a simple and fast iterative algorithm, named SCAOS (simple counterpropagation algorithm for optical signals), for simulating the counterpropagation of optical signals within a nonlinear fiber. Being based on the split-step Fourier method, the algorithm is easily implementable in many traditional optical simulators. Applications of the SCAOS algorithm to the vectorial nonlinear counterpropagation of a polarized pump and a probe signal demonstrate the phenomenon of lossless polarization attraction. The evolution of the signal polarization along the fiber, obtained by simulation, reveals that polarization attraction always entails a certain amount of degradation of the signal’s degree of polarization. Two different setups are studied, involving different types of fibers with Kerr nonlinearity, and highlighting the dependence of the attraction phenomenon, as well as of its effectiveness, on the fiber type
Advanced matrix laser lithography for fabrication of photonic micro-structures
Get PDFDirect laser beam writing techniques represent an interesting alternative to focused electron and ion beam writing approaches for the fabrication of photonic micro-structures. Although the resolution of laser beam writers is strongly limited by the Rayleigh diffraction limit, it is not always necessary to create features significantly smaller than the recording wavelength. In such cases, a laser exposure can be used, with all its advantages. In this paper a direct laser writing technique is presented one; which significantly improves the performance of commonly used direct laser writers by introducing an exposure of a large area within a single step. The elementary exposed area can contain a general micro-structure without any special requirements. In contrast to writing techniques based on a single spot focus, the writing beam can have the shape of a general aperiodic structure and exposes an area of about 10^-2 square millimetre. This complicated exposure field is created using a demagnified projection of the exposed structure from a two-dimensional computer-driven spatial light modulator. The main advantages of the method compares to the single point exposure are a significantly improved exposure speed, a perfect alignment of features within a single exposed area, and the possibility of tuning the exposing field very precisely using continuous modulation of the signal on the spatial light modulator. The in-house-developed device is presented together with several realized samples
Ultra-High Temperature Ceramics for solar receivers: spectral and high-temperature emittance characterization
Get PDFWe report on the preparation, room temperature spectral reflectance and high-temperature thermal emittance characterization of different boride and carbide Ultra-High Temperature Ceramics (UHTCs). The investigated samples are compared with a reference material for solar absorber applications, i.e. silicon carbide. We show that spectral and thermal emittance properties of UHTCs are promising for novel solar receivers
Effect of the Metallization on the Resonances of THz Fishnet Metamaterials
Get PDFIn this numerical study, the influence of the choice of metal (and hence of the conductivity) used for the fabrication of THz fishnet metamaterials is investigated. We explore an exemplary structure for which surface-plasmon-polaritons offer – assuming sufficiently good conductivity – pronounced extraordinary transmission and strong multiple magnetic resonances with negative permeability. We analyze the dependence of these signatures on the type of metallization. Studying five different metals, we find that the metallization is important for achieving the multiple resonances. A reduction of the conductivity can lead to a dramatic weakening and even a near-disappearance of magnetic resonances if they lose their diamagnetic character
Unresonant interaction of laser beams with microdroplets
Get PDFThe interaction of distilled water microdroplets (volumes of 3-4μl) with pulsed laser beams emitted at 532nm is described. At 532nm the distilled water absorption is very low and the interaction of a water bead with the laser radiation is dominated by unresonant phenomena. Following the collision of the laser beam with a microdroplet in suspended/ hanging/pendant position in air, deformations and mechanical vibrations of the droplets are produced. The conditions in which the droplets lose material as a consequence of the impact with laser beams are also explored. The effects produced on the droplet were studied pulse by pulse and depend on: droplet’s content, beam wavelength, power and focusing conditions, irradiation geometry and adhesion of the bead to the capillary on which it is suspended. The laser pulses energies were varied in four steps: 0.25mJ, 0.4mJ, 0.7mJ and 1mJ. The pulse full time width was 5ns and the typical focus diameter on the droplet was 90μm; the beam had a relatively low divergence around the focus point. The microdroplets and the modification/evolution of their shapes are visualised by recordings performed at 10kframes/second. Following a microdroplet interaction with the laser beam one may also produce at a controlled moment in time nanodroplets propagating at high (probably supersonic) speeds and microdroplets propagating at slower speeds. One may also produce pendant droplets of smaller dimensions than the initial one as well as micro/nano gas bubbles in the pendant droplet’s material/volume. In a second set of experiment was recorded at high speed the behaviour of the microdroplets of Rhodamine 6G in distilled water at resonant interaction with similar laser pulses, at the same power levels. The optical phenomena considering that the microdroplets contents are Newtonian liquids which dominate the beads behaviour at interaction with the laser beams, are discussed
Asymmetric transmission and anomalous refraction in metal nanowires metasurface
Get PDFHere we investigated the asymmetric transmission and the anomalous refraction introduced by a metasurface of bent gold nanowires. The refraction follows the generalized Snell’s law that takes into account the resonant behavior of metallic nanostructures located at the interface between two dielectrics. Measurements performed in the linear optical regime reveal a large sensitivity to the subwavelength features of the gold nanostructures
Distribution of temperature in a single lens due to absorption of light and heat conduction: an adaptive solver
Get PDFWe develop an algorithm for the solution of the stationary heat-equation in a single lens due to absorption of light, heat-conduction and transfer of the heat to the environment while we assume rotational symmetry for the whole situation. The proceeding is based on an easy to implement finite difference scheme, which is best suited for rectangular areas. Therefore, we have to transform the heat equation and the boundary conditions from the original domain, i.e. the surface of section of the lens by the aid of tensor methods to a rectangle. So the algorithm generates a grid, which adopts automatically to the actual shape of the lens. In this sense, we characterize the method as adaptive. In the examples, we investigate the effect of a high-transmission glass on the distribution of temperature and further demonstrate the adjustment to a realistic lens shape with a strong deviation from a spherical surface in form of a kink near the edge. We compare the results with a simple model for the distribution of temperature and show the strong dependency of the results on the transmission of the materials
Scanning effects in coherent fourier scatterometry
Get PDFIncoherent Fourier Scatterometry (IFS) is a successful tool for high accuracy nano-metrology. As this method uses only far field measurements, it is very convenient from the point of view of industrial applications. A recent development is Coherent Fourier Scatterometry (CFS) in which incoherent illumination is replaced by a coherent one. Through sensitivity analyses using rigorous electromagnetic simulations, we show that the use of coherence and multiple scanning makes Coherent Fourier Scatterometry (CFS) more sensitive than Incoherent Fourier Scatterometry (IFS). We also report that in Coherent Fourier Scatterometry it is possible to determine the position of the sample with respect to the optical axis of the system to a precision dependent only on the experimental noise
Single Photon Counting with Silicon Photomultipliers, shortening systems and incoherent illumination
Get PDFIn this work it is shown the benefit of using pulse shortening systems for conforming photodetection pulses provided by Silicon Photomultipliers (SiPMs). One of the main drawbacks when using SiPMs is the slow falling edge in the detection signal which can reach even hundreds of nanoseconds. Pulses obtained when using the shortening systems proposed here are single narrow peaks, with full width at half maximum (FWHM) around 10 ns, preserving the photonic modulation and with good pseudo-gaussian shape, single polarity and low ringing. Different tests are presented to illustrate the advantage of these systems in the detection of single photons emitted in short, incoherent pulses