| 1. |
- Adsten, M, et al.
(författare)
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Optical characterization of industrially sputtered nickel-nickel oxide solar selective surface
- 2000
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Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 68:4, s. 325-328
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Tidskriftsartikel (refereegranskat)abstract
- Tandem absorbers are often used in the design of solar absorbers for photo thermal conversion. They consist of a thin coating, selectively absorbing in the wavelength range of the solar spectrum, on a metal substrate. The optical performance of a tandem absorber depends on the optical constants and thickness of the absorbing coating and also on the reflectivity of the underlying metal. A very high solar absorptance is achieved when the coating has a non-uniform composition in the sense that the refractive index is highest closest to the metal substrate and then gradually decreases towards the front surface. This type of composition suppresses coating interference and gives a low front surface reflection if the refractive index at the front surface is low. We report on optical analysis of a, Solar absorber with a graded index coating of sputtered nickel-nickel oxide deposited on aluminium. The optical constants have been determined from reflectance, transmittance and ellipsometry data by fitting the data to a two-layer model of the coating. The optical constants of the two layers can be regarded as effective optical constants for the lower and upper part of the graded index coating respectively. It is found that the effective refractive index of the top layer is somewhat tower than for the base layer. The extinction coefficient is higher in the lower part of the coating. Both effective refractive index and extinction coefficient of the base layer increase monotonically with increasing wavelength as for metallic materials. (C) 2000 Elsevier Science Ltd. All rights reserved.
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| 2. |
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| 3. |
- Ahuja, Rajeev, et al.
(författare)
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Optical properties of 4H-SiC
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2099-2103
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Tidskriftsartikel (refereegranskat)abstract
- The optical band gap energy and the dielectric functions of n-type 4H-SiC have been investigated experimentally by transmission spectroscopy and spectroscopic ellipsometry and theoretically by an ab initio full-potential linear muffin-tin-orbital method. We present the real and imaginary parts of the dielectric functions, resolved into the transverse and longitudinal photon moment a, and we show that the anisotropy is small in 4H-SiC. The measurements and the calculations fall closely together in a wide range of energies.
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| 4. |
- Akerlind, C, et al.
(författare)
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Optical properties and switching of a Rose Bengal derivative: A spectroscopic ellipsometry study
- 2011
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Ingår i: THIN SOLID FILMS. - : Elsevier Science B.V., Amsterdam.. - 0040-6090. ; 519:11, s. 3582-3586
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Tidskriftsartikel (refereegranskat)abstract
- Optical properties in terms of the complex-valued dielectric function were determined for spin-coated films of a Rose Bengal derivative using variable angle of incidence spectroscopic ellipsometry in the visible and infrared wavelength regions. In addition, the thickness and roughness of the films were determined and related to the solution concentration of Rose Bengal. Switching between two different oxidation states of the Rose Bengal derivative was investigated. The two states were chemically induced by exposure to vapors of hydrochloric acid and ammonia, respectively. A substantial and reversible change of the optical properties of the films was observed.
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| 5. |
- Akerlind, C., et al.
(författare)
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Optical Studies of White Organic Materials for Camouflage Applications in Arctic Environments
- 2022
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Ingår i: TARGET AND BACKGROUND SIGNATURES VIII. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510655447
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Konferensbidrag (refereegranskat)abstract
- Important properties for camouflage materials can be summarized in six criteria: (1) spectrally selective reflectance, (2) low gloss, (3) low degree of polarization, (4) low infrared emissivity, (5) non-destructive effect on radar properties and (6) color adaptivity. We have studied a collection of natural materials for potential use as camouflage surfaces for the arctic region. The four first camouflage criteria are analyzed using spectrometry, scatterometry and spectroscopic ellipsometry techniques. The materials involved in the study are diffuse white nature-inspired surfaces: Cuticles of the beetle Cyphochilus insulanus, and foams of freeze-casted cellulose nanofibrils. We present data that partly fulfills the addressed camouflage criteria. An adequate reflectance is achieved in the spectral range of 400 - 1600 nm for both samples. Scattering data show that near-Lambertian properties are achieved at 633 nm for both surfaces but at 1550 nm for only the beetle cuticle. The degree of polarization is low for unpolarized light incident near the surface normal for both surfaces.
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| 6. |
- Arwin, Hans, 1950-, et al.
(författare)
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Analysis of Mueller-matrix data from chiral structures in exoskeletons of scarab beetles
- 2012
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Several species of scarab beetles exhibit extra-ordinary metallic-like structural colors. These color-generating structures also show complex polarization properties and unpolarized light can be reflected with near-circular polarization. Specimens of Cetonia aurata (Linnaeus, 1758) are here studied with a dual-rotating compensator ellipsometer using focusing probes. Mueller-matrix data are recorded with precision better than ±0.005 in the range 350 – 1000 nm for angles 20-60º. In a narrow spectral range in the green part of the spectrum, the Mueller-matrix elements m14 and m41 show large negative values and the reflected light is near-circular left-handed polarized. This effect originates from a chiral structure in the beetle exoskeleton. A twisted biaxial lamellae structure with a top dielectric layer is used in regression analysis to determine pitch of the helix and refractive indices of the chitin-based constituting materials. The applicability of this model to data from different scarab beetles is reviewed and it is found that the model show limitations for beetles with broad-band reflection, e.g. those with gold-like colors. For narrow-band optical features, the model provides an excellent fit for all 15 normalized Mueller-matrix elements over the full spectrum and angle of incidence range. Dispersion models like Cauchy, b-splines and oscillator-based models are employed for the biaxial layer and fit qualities for the tested models are compared.
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| 7. |
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| 8. |
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| 9. |
- Arwin, Hans, et al.
(författare)
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Chirality-induced polarization effects in the cuticle of scarab beetles: 100 years after Michelson
- 2012
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Ingår i: Philosophical Magazine. - : Taylor and Francis: STM, Behavioural Science and Public Health Titles / Taylor and Francis. - 1478-6435 .- 1478-6443. ; 92:12, s. 1583-1599
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Tidskriftsartikel (refereegranskat)abstract
- One hundred years ago Michelson discovered circular polarization in reflection from beetles. Today a novel Mueller-matrix ellipsometry setup allows unprecedented detailed characterization of the beetles polarization properties. A formalism based on elliptical polarization for description of reflection from scarab beetles is here proposed and examples are given on four beetles of different character: Coptomia laevis - a simple dielectric mirror; Cetonia aurata - a left-hand narrow- band elliptical polarizer; Anoplognathus aureus - a broad-band elliptical polarizer; and Chrysina argenteola - a left-hand polarizer for visible light at small angles, whereas for larger angles, red reflected light is right-handed polarized. We confirm the conclusion of previous studies which showed that a detailed quantification of ellipticity and degree of polarization of cuticle reflection can be performed instead of only determining whether reflections are circularly polarized or not. We additionally investigate reflection as a function of incidence angle. This provides much richer information for understanding the behaviour of beetles and for structural analysis.
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| 10. |
- Arwin, Hans, 1950-, et al.
(författare)
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Comparison and analysis of Mueller-matrix spectra from exoskeletons of blue, green and red Cetonia aurata
- 2014
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 571, s. 739-743
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Tidskriftsartikel (refereegranskat)abstract
- The exoskeleton, also called the cuticle, of specimens of the scarab beetle Cetonia aurata is a narrow-band reflector which exhibits metallic shine. Most specimens of C. aurata have a reflectance maximum in the green part of the spectrum but variations from blue–green to red–green are also found. A few specimens are also more distinct blue or red. Furthermore, the reflected light is highly polarized and at near-normal incidence near-circular left-handed polarization is observed. The polarization and color phenomena are caused by a nanostructure in the cuticle. This nanostructure can be modeled as a multilayered twisted biaxial layer from which reflection properties can be calculated. Specifically we calculate the cuticle Mueller matrix which then is fitted to Mueller matrices determined by dual-rotating compensator ellipsometry in the spectral range 400–800 nm at multiple angles of incidence. This non-linear regression analysis provides structural parameters like pitch of the chiral structure as well as layer refractive index data for the different layers in the cuticle. The objective here is to compare spectra measured on C. aurata with different colors and develop a generic structural model. Generally the degree of polarization is large in the spectral region corresponding to the color of the cuticle which for the blue specimen is 400–600 nm whereas for the red specimen it is 530–730 nm. In these spectral ranges, the Mueller-matrix element m41 is non-zero and negative, in particular for small angles of incidence, implicating that the reflected light becomes near-circularly polarizedwith an ellipticity angle in the range 20°–45°.
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