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  • 1.
    Bergström, David
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Powell, John
    Laser Expertise Ltd., Nottingham, United Kingdom.
    Kaplan, Alexander
    Luleå University of Technology.
    Absorptance of Non-Ferrous Alloys to Nd:YLF and Nd:YAG Laser Light at Room Temperature2007In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 46, no 8, p. 1290-1301Article in journal (Refereed)
    Abstract [en]

    The measurement of absorptance is important for the analysis and modelling of laser-material interactions. Unfortunately, most of the absorptance data presently available considers only polished pure metals rather than the commercially available (unpolished, oxidised) alloys which are actually being processed in manufacturing. This paper presents the results of absorptance measurements carried out at room temperature on as-received engineering grade non-ferrous metals (Al, Cu and Zn alloys). The measurements were made using an integrating sphere with an Nd:YLF laser at two wavelengths (1053nm and 527nm � which means that the results are also valid for Nd:YAG radiation at 1064nm and 532nm). The absorptance results obtained differ considerably from existing data for polished, pure metals and should help improve the accuracy of laser-material interaction models. Some clear trends were identified. For all 22 cases studied the absorptance was higher than for ideal pure, polished metals. For all Al- and Cu-samples the absorptance was higher for the green than it was for the infrared wavelength, while for all Zn-coatings this trend was reversed. No clear correlation between absorptance and surface roughness was found at low roughness values (Sa 0.15 � 0.60) but one, rougher set of samples (Sa 2.34), indicated a roughness-absorptance correlation at higher roughness levels.

  • 2.
    Gustafsson Coppel, Ludovic
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Andersson, Mattias
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Determination of quantum efficiency in fluorescing turbid media2011In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, no 17, p. 2784-2792Article in journal (Refereed)
    Abstract [en]

    A method is proposed to estimate the optical parameters in a fluorescing turbid medium with strong absorption for which traditional Kubelka–Munk theory is not applicable, using a model for the radiative properties of optically thick fluorescent turbid media of finite thickness proposed in 2009[J. Opt. Soc. Am. A26, 1896 (2009)JOAOD60740-323210.1364/JOSAA.26.001896]. The method is successfully applied to uncoated papers with different thicknesses. It is found that the quantum efficiency of fluorescent whitening agents (FWAs) is nearly independent of the fiber type, FWA type, FWA concentration, and filler additive concentration used in this study. The results enable an estimation of the model parameters as function of the FWA concentration and substrate composition. This is necessary in order to use the model for optimizing fluorescence in the paper and textile industries.

  • 3.
    Jason, Johan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Arvidsson, Bertil
    Fiberson AB, Fibervagen 2, Hudiksvall SE-824 11, Sweden.
    Larsson, Anders
    Fiberson AB, Fibervagen 2, Hudiksvall SE-824 11, Sweden.
    Robustness analysis of an intensity modulated fiber-optic position sensor with an image sensor readout system2013In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 52, no 16, p. 3876-3883Article in journal (Refereed)
    Abstract [en]

    An intensity modulated fiber-optic position sensor, based on a fiber to bundle coupling and a readout system using a CMOS image camera together with fast routines for position extraction and calibration, is presented and analyzed. The proposed system eliminates alignment issues otherwise associated with coupling based fiber-optic sensors, still keeping the sensing point free from detector electronics. In this study the robustness of the system is characterized through simulations of the system performance, and the outcome is compared with experimental results. It is shown that knowledge of the shape of the coupled power distribution is the single most important factor for high performance of the system. Further it is experimentally shown that the position extraction error can be improved down to the theoretical limit by employing a modulation function model well fitted to the real coupled power distribution.

  • 4.
    Jason, Johan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. Fiberson AB, SE-82450 Hudiksvall, Sweden.
    Rugeland, Patrik
    Acreo Swedish ICT AB, SE-16440 Stockholm, Sweden.
    Tarasenko, Oleksandr
    Acreo Swedish ICT AB, SE-16440 Stockholm, Sweden.
    Margulis, Walter
    Acreo Swedish ICT AB, SE-16440 Stockholm, Sweden.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Temperature characteristics of the birefringence properties of filled side-hole fibers2013In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 52, no 21, p. 5208-5215Article in journal (Refereed)
    Abstract [en]

    The temperature characteristics of the birefringence of side-hole fibers filled with liquids or metal are investigated, aiming at providing a basis for on/off temperature sensing. Short pieces of fiber are filled and the change in birefringence is registered using measurements in reflective mode of the transmitted power through a linear polarizer at 1550 nm. The rapid change in the birefringence behavior of the fiber at the temperature of the phase transition of the filler substance is shown, and from the measurement data the phase transition temperatures can be determined as well as an estimation of the birefringence change with temperature. The experimental results are supported by numerical simulations.

  • 5.
    Johansson, Niklas
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Neuman, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Andersson, Mattias
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Influence of finite-sized detection solid angle on bidirectional reflectance distribution function measurements2014In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 53, no 6, p. 1212-1220Article in journal (Refereed)
    Abstract [en]

    This paper deals with limitations and often overlooked sources of error introduced in compact double-beam goniophotometers. It is shown that relative errors in measured radiance factor, comparable to the total measurement uncertainty, can be introduced if recommended corrections are not carried out. Two different error sources are investigated, both related to the size of the detection solid angle. The first is a geometrical error that occurs when the size of the illuminated area and detector aperture are comparable to the distance between them. The second is a convolution error due to variations in radiant flux over the detector aperture, which is quantified by simulating the full 3D bidirectional reflectance distribution function (BRDF) of a set of samples with different degrees of anisotropic reflectance. The evaluation is performed for a compact double-beam goniophotometer using different detection solid angles, and it is shown that both error sources introduce relative errors of 1%–3%, depending on viewing angle and optical properties of the sample. Commercially available compact goniophotometers, capable of absolute measurements, are becoming more and more common, and the findings in this paper are therefore important for anyone using or planning to use this type of instrument.

  • 6.
    Johansson, Niklas
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Neuman, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Andersson, Mattias
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Separation of surface and bulk reflectance by absorption of bulk scattered light2013In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 52, no 19, p. 4749-4754Article in journal (Refereed)
    Abstract [en]

    A method is proposed for separating light reflected from turbid media with a rough surface into a bulkand a surface component. Dye is added to the sample, thereby increasing absorption and canceling bulkscattering. The remaining reflected light is surface reflectance, which can be subtracted from the totalreflectance of an undyed sample to obtain the bulk component. The method is applied to paper wherethe addition of dye is accomplished by inkjet printing. The results show that the bulk scattered light isefficiently canceled, and that both the spectrally neutral surface reflectance and the surface topographyof the undyed paper is maintained. The proposed method is particularly suitable for characterization ofdielectric, highly randomized materials with significant bulk reflectance and rough surfaces, which aredifficult to analyze with existing methods. A reliable separation method opens up for new ways of analyzing,e.g., biological tissues and optical coatings, and is also a valuable tool in the development of morecomprehensive reflectance models.

  • 7.
    Neuman, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    G. Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Angle resolved color of bulk scattering media2011In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, no 36, p. 6555-6563Article in journal (Refereed)
    Abstract [en]

    The angle resolved reflectance factor of matte samples is measured with a goniophotometer and simulated using radiative transfer theory. Both measurements and simulations display the same characteristic dependence of the reflectance factor on the observation angle. The angle resolved reflectance spectra are translated to CIELAB color coordinates and the angular color differences are found to be surprisingly large. A chromatic adaptation that is dependent on the observation angle is suggested, in which a nonabsorbing opaque medium is used as the reference white, and the angular color differences are then reduced. Furthermore, the use of an undyed paper as the reference white is evaluated. The angular lightness differences are then reduced further, but the angular differences in chroma are still large. It is suggested that smaller variations in perceived color could be explained by angle dependent chromatic adaptation and a limited sensitivity of the human visual system to changes in chroma.

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