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Silicon nano-crystals have been studied intensively due to their photoluminescence properties and possible applications in new generation opto-electronic devices. Their importance in lightning and display technologies is increasing due to the abundance and non-toxicity of silicon. Here we report a single batch solution based synthesis route to silicon nano-crystal organic hybrid films exhibiting white light photoluminescence at room temperature upon excitation by ultraviolet light. Films prepared by ethylene glycol terminated Si nano-crystals showed maximum 240 nm red shift in photoluminescence response upon excitation at 350 nm. The shift was found to decrease in order for hybrid films fabricated using acrylic acid, 1-octanol acid and oleic acid terminated Si nano-crystals. The mean size of the Si nano-crystals (~ 2–10 nm) estimated by Raman spectroscopy were smallest for the ethylene glycol capped Si nano-crystal films. The calculated Tauc bandgaps of the hybrid films varied between 1.51 and 2.35 eV.

Coral reefs around the world are under threat due to anthropogenic impacts on the environment. It is therefore important to develop methods to monitor the status of the reefs and detect changes in the health condition of the corals at an early stage before severe damage occur. In this work, we evaluate underwater hyperspectral imaging as a method to detect changes in health status of both orange and white color morphs of the coral species Lophelia pertusa.Differing health status was achieved by exposing 66 coral samples to the toxic compound 2-methylnaphthalene in concentrations of 0 mg L−1 to 3.5 mg L−1. A machine learning model was utilized to classify corals according to lethal concentration (LC) levels LC5 (5 % mortality) and LC25 (25 % mortality), solely based on their reflectance spectra. All coral samples were classified to correct concentration group. This is a first step towards developing a remote sensing technique able to assess environmental impact on deep-water coral habitats over larger areas.

We surveyed the deposition of drill cuttings on the seafloor along a transect at eight drilling locations in the south-western Barents Sea and Norwegian Sea, comparing traditional visual surveying methods and underwater hyperspectral imagery (UHI). The locations range from newly-drilled to around 30 years post-drilling. The visual assessments detected deposited drill cuttings to extend to around 150–200 m from the drilling location at recently drilled sites and generally less than 50 m at older locations. Quantitative UHI analyses of relative change in the spectral signature of the sediments with increasing distance from the drilling location mostly showed a change-over to conditions resembling undisturbed sediments at approximately similar distances as the visual assessments. Biological faunal community analyses also reflected these trends. The UHI-based detection of drill cuttings thus in general supported the results of visual assessments and potentially could be further developed as a method for automated surveying of drilling sites.

Currently a new underwater hyperspectral imager (UHI) have been deployed on Remotely Operated Vehicles (ROV) for a more automated identification, mapping and monitoring of bio-geo-chemical objects of interest (OOI). Sea floor maps based on UHI can be used to classify 001 based on specific optical fingerprints providing spectral upwelling radiance or reflectance with up to 1 nm spectral resolution in the visible range for each image pixel. Different habitats comprising soft bottom, deep and cold water coral reefs, sponge habitats, pipeline monitoring and kelp forest maps are examples for UHI-based mapping. Characterising material surface on man-made objects such as corrosion on pipelines and subsea structures and archaeological objects are other examples. The overall image quality and identification success of OOI can be optimized if movements of the ROV is controlled by a dynamic position (DP) system and corresponding speed, altitude, pitch, roll and yaw control. Likewise, illumination control is important to provide proper light intensity, spectral composition and illumination evenness of OOI to enhance data quality. The benefits of using UHI for seafloor habitat mapping can be evaluated by four categories of resolution. These are A) spatial resolution (image pixel size), B) spectral resolution (1-10 nm, 400-800 nm), C) radiometric resolution (dynamic range, bits per pixel), and D) temporal resolution for time-series and monitoring. These categories of resolution are discussed with respect to OOI identification and mapping using different case examples.

During an expedition to the Atlantic Mid-Ocean ridge in August 2016, an underwater hyperspectral imager (UHI) was utilized. The target was to investigate its applicability to exploration for marine minerals. The imager was deployed on both an autonomous underwater vehicle (AUV) and a remotely operated vehicle (ROV). To the authors knowledge, this is the first time a full scale hyperspectral imager has been mounted on an AUV. This new platform comes with many advantages and drawbacks which will be discussed, both in terms of future potential and observed data quality.

The design of complete broadband polarimeters with high performance is challenging due to the wavelength dependence of optical components. An efficient genetic algorithm computer code was recently developed in order to design and re-optimize complete broadband Stokes polarimeters and Mueller matrix ellipsometers. Our results are improvements of previous patented designs based on two and three ferroelectric liquid crystals (FLCs). FLC based polarimeters are suited for broadband hyperspectral imaging, or multichannel spectroscopy applications. We have realized and implemented one design using two FLCs and compare the spectral range and precision with previous designs.

A partial in and out of incidence plane Mueller matrix scattering ellipsometry (MMSE) experiment is presented, where the Stokes vectors of the scattered light are detected in slightly more than a quarter hemisphere. The MMSE system is briefly reviewed. The Mueller scattering matrix obtained in reflection from as-cut rough solar grade mc-Si surfaces is reported. For the as-cut surface with an estimated correlation length of 4 μm and root mean square roughness of 550 nm, using an illumination wavelength of 532 nm, the degree of polarization is observed to be larger than 0.86, even far away from the incidence plane.

Producing surfaces textured with a homogeneous pattern of nanoscale structures is increasingly important for fabrication of semiconductor devices. Although techniques exist for imaging surface nanostructures on a local scale, these techniques are often impractical for use over large areas for finding average structural information. The nanostructured surface in this study consists of densely packed cones produced by sputtering a mono-crystalline GaSb substrate with a low-energy unfocused ion beam, yielding self-organized cones that are slightly tilted away from the sample normal. Here, we devise an all-optical non-destructive characterization scheme using Grazing-Incidence Small-Angle X-ray Scattering (GISAXS) and Spectroscopic Mueller Matrix Ellipsometry (MME) for obtaining all main dimensions including average height, lateral spacing and packing motifs, and the cone top and bottom diameters. It is further shown that both MME and GISAXS are sensitive to small tilts of the nanocone axis from the surface normal.

Small-scale solidification simulations were carried out in order to study the effect of the grain orientation and cooling rate on the stresses in mono- and bi-crystals. First, a 2D-axisymetric heat-transfer model of the global furnace is established to provide input to the sub-model. The sub-model takes into account only the crucible and silicon ingot. The flux histories are transferred from the global model. A finite element crystal plasticity model solves the mechanical deformation in the ingot. Ingots were grown in the small-scale Bridgman furnace with different pulling rates ranging from 0.2 to 50 mm/min. The results show the asymmetric effect of the crystal orientation and the stress build-up at the grain boundary due to different orientations. The change in pulling rate affects strongly the solidification front shape and the residual stresses. The 3D mechanical model illustrates also the limitations of the 2D-axisymmetric approach when silicon crystal anisotropy is taken into account.

Salmon louse, or sea lice, (Lepoptherius salmonis) represents practical, economical and fish welfare challenges for salmon farming (Hamre et al., 2013) and for the free-living stocks of salmon. There is an urgent need in the industry for a system that provides reliable numbers of louse on farmed salmon. Underwater hyperspectral imaging represents a potential new technique for louse counting in sea cages. In laboratory studies, the UHI technology could detect and classify pre-adults (pre-adult I and II), adult males and adult females (ovigerous) of sea lice based on the difference in their spectral characteristics. A model was built for detection of lice on the salmon and the UHI had a detection success ranging from 67 to 100 % with an average of 82%. A classification of the detected lice was performed for pre-adults, adult males and ovigerous lice and had a prediction accuracy of 85% when lice were divided into three groups (pre-adults, adult male and ovigerous lice) and 93% when lice were divided in two groups, ovigerous lice and all the other mobile lice (pre-adults and adult male). An automatic procedure for in situ measurements of louse infected salmon could deliver a data basis several times higher than the traditional counting system. The next generation of UHI louse detector should be developed with a higher spatial resolution to be able to detect also the sessile stages of lice. For succeeding with in situ classification of L. salmonis, correction algorithms to compensate for the impact of water between the UHI and lice need also to be developed.

A gold nanowired grid polarizer is studied in the mid-IR range by means of spectroscopic Mueller matrix ellipsometry. This material is also an example of a so-called 2-dimensional hyperbolic metamaterial/metasurface, and produced by low-cost large area scalable manufacturing techniques. We present the IR spectroscopic Mueller matrix optical response of such sample for a full azimuthal rotation. It is observed strong in-plane anisotropy due to the gold wire grid. The main objective is to show a characterization methodology to reveal the complete polarimetric response over a large spectral range, providing information about the effective optical properties of the sample. Three different optical models are proposed that catch the main features of experimental data. The first one is based on the Rigorous Coupled-Wave Analysis (RCWA) assuming the profile of the sample to be periodic, second, a Generalized Effective Medium Approximation (G-EMA) assuming oriented gold ellipsoids aligned along the lines of the wire grid, and third, a biaxial dispersion model. Experimental data is compared with simulated data obtained from the three optical models and a comparative analysis between them is presented. The different models allow to retrieve information on the characteristic dimensions of the nanowires, and also to obtain the two in-plane components of the effective dielectric tensor of the nanostructured layer. The tensor component parallel to the nanowires shows a metallic response whereas the component perpendicular to them behaves as a transparent dielectric. Moreover, we have also shown that the nanowired grid behaves as a hyperbolic material.

We report on the design and performance of a near infra-red Mueller matrix imaging ellipsometer, and apply the instrument to retardance imaging of strain in near infra-red transparent solids. Particularly, we show that the instrument can be used to investigate complex strain domains in multi-crystalline silicon wafers.

The dynamic response of a near infrared Ferroelectric Liquid Crystal based Mueller matrix ellipsometer (NIR FLC-MME) is presented. A time dependent simulation model, using the measured time response of the individual FLCs, is used to describe the measured temporal response. Furthermore, the impulse response of the detector and the pre-amplifier is characterized and included in the simulation model. The measured time-dependent intensity response of the MME is reproduced in simulations, and it is concluded that the switching time of the FLCs is the limiting factor for the Mueller matrix measurement time of the FLC-based MME. Based on measurements and simulations our FLC based NIR-MME system is estimated to operate at the maximum speed of approximately 16 ms per Mueller matrix measurement. The FLC-MME may be operated several times faster, since the switching time of the crystals depends on the individual crystal being switched, and to what state it is switched. As a demonstration, the measured temporal response of the Mueller matrix and the retardance of a thick liquid crystal variable retarder upon changing state is demonstrated., to be published in Journal of Modern Optics 20 pages, 6 figures

Underwater hyperspectral imaging is a novel method for mapping and monitoring the seafloor. It uses the reflected light from objects under water to automatically identify them. This paper explains the basic technology and shows examples of use from two field missions in Norwegian waters. In the two cases, libraries of spectral signatures for the living organisms at the site were established, and subsequently used to automatically identify objects on the seafloor.

We have investigated the structural and optical properties of Cr-doped ZnS (ZnS:Cr) thin films (0–7.5 at.% Cr) for use in intermediate band solar cells. The films were grown on Si(100) in molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) equipments. Introducing Cr into ZnS resulted in Cr related subbandgap absorption, but also reduced the grain size. The sub-bandgap absorption increased with increasing Cr content, and with increasing growth temperature, but did not depend on the growth method. In contrast, the crystallinity depended strongly on the growth method, and smoother and highly textured films were obtained by PLD. The data indicate that stacking faults are present in all films. This is the authors' submitted manuscript of an article published by Elsevier in Solar Energy Materials and Solar Cells.

A method for measuring three-dimensional (3-D) direction images of collagen fibers in biological tissue is presented. Images of the 3-D directions are derived from the measured transmission Mueller matrix images (MMIs), acquired at different incidence angles, by taking advantage of the form birefringence of the collagen fibers. The MMIs are decomposed using the recently developed differential decomposition, which is more suited to biological tissue samples than the common polar decomposition method. Validation of the 3-D direction images was performed by comparing them with images from second-harmonic generation microscopy. The comparison found a good agreement between the two methods. It is envisaged that 3-D directional imaging could become a useful tool for understanding the collagen framework for fibers smaller than the diffraction limit. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Broadened plasmon resonances of Cu nanoparticles in nanopatterned mixed oxide sol-gel nanopillars are shown to be readily detected by spectroscopic Mueller matrix ellipsometry. The plasmonic nanomaterials are obtained by low energy ion sputtering of a CuO sol-gel film. Both s- and p-polarized plasmon resonances are observed in the off-block-diagonal and the block-diagonal Mueller matrix elements as well as in the generalized ellipsometric parameters. The resonant features in all elements correlate with both maximum depolarization and a minimum in the reflected intensity. The spectral position and the polarization character of the plasmon resonances are discussed phenomenologically through effective medium theory. © 2013 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited.

International audience; We demonstrate that small tilts away from the substrate normal, of short (30-40 nm high) nanopillars, may be detected and modeled by spectroscopic UV-Visible Mueller Matrix Ellipsometry (MME). The pillars were produced by sputtering a GaSb substrate with a low energy unfocused ion beam. It has previously been found that the pillars will point in the direction of the ion flux. For both samples reported here, the ion-incidence was unintentionally tilted away from the substrate normal by 2.8 and 4.8°. The MME measurements were performed using both multiple angles of incidence, and 360° rotation of the incidence plane. Graded uniaxial effective medium models were fitted to the experimental data, and through Euler angle rotations of the dielectric tensor, the tilt angle and the orientation of the pillar direction, were obtained. The UV part of the spectrum enhanced the tilt angle sensitivity down to 0.02-0.05°. A data presentation that enhances the understanding of the symmetry in the crystallographic information obtained from spectroscopic MME is proposed. The off block diagonal Mueller matrix elements are more sensitive to the in-plane anisotropy, whereas for small tilt angles m14 scales approximately with θsin(ϕ).

Gold nanoparticles deposited on self-organized nano-ripple quartz substrates have been studied by spectroscopic Mueller matrix ellipsometry. The surface was found to have biaxial anisotropic optical properties. For electric field components normal to the ripples the periodic and disconnected nature of the in plane nanowires gives rise to an optical response dominated by the localized plasmon resonance. In the direction parallel to the ripples the gold nanoparticles are aligned closely leading to localized plasmon resonances in the infrared. As Au was deposited at an angle oblique to the surface normal, the gold nanoparticles were formed on the side of the ripples facing the incoming evaporation flux. This makes the gold particles slightly inclined, correspondingly the principal coordinate system of the biaxial dielectric tensor results tilted. The anisotropic plasmonic optical response results in a strong polarizing effect, making it suitable as a plasmonic nanowired grid polarizer. © 2013 Optical Society of America. Open access.

Decomposition methods have been applied to in-plane Mueller matrix ellipsometric scattering data of the Spectralon reflectance standard. Data were measured at the wavelengths 532 nm and 1500 nm, using an achromatic optimal Mueller matrix scatterometer applying a photomultiplier tube and a high gain InGaAs detector for the two wavelengths. A parametric model with physical significance was deduced through analysis of the product decomposed matrices. It is found that when the data are analyzed as a function of the scattering angle, similar to particle scattering, the matrix elements are largely independent of incidence angle. To the first order, we propose that a Guassian lineshape is appropriate to describe the polarization index, while the decomposed diagonal elements of the retardance matrix have a form resembling Rayleigh single scattering. New models are proposed for the off diagonal elements of the measured Mueller matrix. © 2013 Optical Society of America. Open access.

The full Mueller matrix was measured to obtain the polarization state of the scattered light for a variety of algae with different shapes, wall compositions, sizes, and refractive indices. The experimental setup was a multiple laser Mueller matrix ellipsometer, by which measurements were performed for scattering angles from 16° to 160° sampled at every second degree for wavelengths of 473 nm and 532 nm. Previously, the polarization of light scattered from microalgae was investigated only for a few species, and the Mueller matrix was found to have little variation between the species. In our work a total of 11 algal species were investigated, representing diatoms, dinoflagellates, coccolithophorids, green algae, and a cryptophyte. The selection of species was made to obtain high variability in shape, size, cell wall, and refractive index. As in previous investigations, very small variations were found between species for most of the Mueller matrix elements, but noticeable variations were found for M(11), (M(12)+M(21))/2 and (M(33)+M(44))/2.

A Mueller Matrix Imaging Ellipsometer system is operated in transmission and used to study nematic textures in colloidal dispersions of synthetic Na-fluorohectorite clay platelets in solution. It is clearly observed that the anisometric particles organize into phases with strong birefringence, which results in a strong retardance. The Mueller matrix imaging technique supplies an image of the retardance matrix, even in the presence of other effects such as light scattering and diattenuation. The spatial variation of the absolute value of the retardance, the orientation of the fast axis of the retardance, the total diattenuation and the orientation of the diattenuation are presented. In particular, from knowledge of the anisotropic shape of the particles, the orientation of the particles within ordered domains, and the density of the particles within the domains are spatially determined. The experiments are based on adding synthetic clay particles into a solution contained in a thin rectangular glass container. Upon letting gravitation act on the sample, different phases appear after a few weeks. One phase contains nematic textures and we are able to determine the ordering and also estimate the density of the domains/texture within the phase, in addition to estimating the local order within a domain with an image resolution of 12 μm.

We present the application of a near infra red Mueller matrix imaging ellipsometer to the characterization of plasmonic polarizers. The samples are prepared by evaporation of Au onto SiO2 ripples. The nanostructured ripple surface has been produced by ion beam sputtering at an off normal angle of incidence. Au was thereafter evaporated onto the surface at an grazing angle. As a result, thin lines of nearly connected Au nanoparticles form along the illuminated side of the ripples, resulting in a large in-plane anisotropy of the structure. Mueller matrix imaging is used to determine the lateral uniformity of the optical signal in correlation to the real space topography of the sample, and to determine to what degree the nanoparticles tend to form a connected wire, or whether there are well separated Au particles. The success of this method in order to produce polarizers, lies in controlling the process to allow well connected lines of Au particles along the ripples, with a high degree of homogeneity. Mueller Matrix images of the sample recorded at normal incidence are shown, and the information that can be extracted from such images is discussed.

The collagen meshwork in articular cartilage of chicken knee is characterized using Mueller matrix imaging and multiphoton microscopy. Direction and degree of dispersion of the collagen fibers in the superficial layer are found using a Fourier transform image-analysis technique of the second-harmonic generated image. Mueller matrix images are used to acquire structural data from the intermediate layer of articular cartilage where the collagen fibers are too small to be resolved by optical microscopy, providing a powerful multimodal measurement technique. Furthermore, we show that Mueller matrix imaging provides more information about the tissue compared to standard polarization microscopy. The combination of these techniques can find use in improved diagnosis of diseases in articular cartilage, improved histopathology, and additional information for accurate biomechanical modeling of cartilage. © 2011 Society of Photo-Optical Instrumentation Engineers (SPIE) . Open Access

A fast multichannel Stokes/Mueller polarimeter with no mechanically moving parts has been designed to have close to optimal performance from 430-2000 nm by applying a genetic algorithm. Stokes (Mueller) polarimeters are characterized by their ability to analyze the full Stokes (Mueller) vector (matrix) of the incident light. This ability is characterized by the condition number, $\kappa$, which directly influences the measurement noise in polarimetric measurements. Due to the spectral dependence of the retardance in birefringent materials, it is not trivial to design a polarimeter using dispersive components. We present here both a method to do this optimization using a genetic algorithm, as well as simulation results. Our results include fast, broad-band polarimeter designs for spectrographic use, based on 2 and 3 Ferroelectric Liquid Crystals, whose material properties are taken from measured values. The results promise to reduce the measurement noise significantly over previous designs, up to a factor of 4.5 for a Mueller polarimeter, in addition to extending the spectral range., Comment: 10 pages, 6 figures, submitted to Optics Express

This paper reports on the design and implementation of a liquid crystal variable retarder based overdetermined spectroscopic Mueller matrix polarimeter, with parallel processing of all wavelengths. The system was designed using a modified version of a recently developed genetic algorithm [Letnes et al. Opt. Express 18, 22, 23095 (2010)]. A generalization of the eigenvalue calibration method is reported that allows the calibration of such overdetermined polarimetric systems. Out of several possible designs, one of the designs was experimentally implemented and calibrated. It is reported that the instrument demonstrated good performance, with a measurement accuracy in the range of 0.1% for the measurement of air.