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Received: 28 Apr 2021 / Revised: 21 Jul 2021 / Accepted: 25 Jul 2021 / Published: 2 Aug 2021. © 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement., The absorption coefficient of a material is classically determined by measuring the transmittance of a homogeneous sample contained within flat optical faces and under collimated illumination. For arbitrary shapes this method is impracticable. The characterization of inhomogeneous or randomly distributed samples such as granules, powders or fibers suffers the same problem. Alternatively, an integrating cavity permits us to illuminate a sample under a homogenous and isotropic light field where the analysis simplifies. We revisit this strategy and present a new formal basis based on simple radiometric laws and principles. We introduce a new concept to describe the absorption: the optical form factor. We tackle a rigorous treatment of several regular forms, including full absorption range and the reflection at its surfaces. We also model and improve an integrating sphere setup to perform reliable measurements. Altogether, it permits achieving simple but general conclusions for samples with arbitrary shape or spatial distribution, from weak to highly absorbing, expanding the applicability of quantitative absorption spectroscopy. Finally, we validate it by measuring different sample formats made of PMMA: a cube, groups of granules and injection molding loose parts. The absorption coefficient of PMMA varies near three orders of magnitude in the explored range (380-1650 nm)., Comunidad de Madrid, Sección Deptal. de Óptica (Óptica), Fac. de Óptica y Optometría, TRUE, pub

Reliable measurements are of utmost importance when investigating the relationship between light and human reactions. The aim of the present study was to compare two methods for measuring light exposure in real working environments. Ambulatory recordings of illuminance and irradiance were compared with static field measurements of horizontal illuminance at the normal working position, average horizontal illuminance in the room, vertical illuminance at the position of the eye in the normal angle of gaze, and spectral composition of the light radiation at the normal working position and at the position of the eye in the normal angle of gaze. The ambulatory measurements were carried out during a 3-day experimental period and were repeated monthly throughout the year. The static field measurements in the subjects’ offices were conducted five times during the year, in the morning and afternoon during one day. The relationship between the illuminances and irradiances measured with the portable instruments and the static measurements was statistically analyzed. Results from the analyses revealed that more than one third of the static measurements of vertical illuminances recorded were below 200 lx, and only 7% of the measurements exceeded 1000 lx. Measurements of the spectral composition of the light radiation in the rooms suggested that the light, although at a fairly low intensity, included relatively much radiation that can have a non-image forming effect. Furthermore, only a small number of significant correlations between the ambulatory and static measurements were found. Results from the t-tests showed that there were no differences between ambulatory measurements, and static measurements of horizontal illuminance at the normal position, average illuminance in the room and vertical illuminance at the position of the eye during three, five, and seven of the 10 measurements, respectively. There is a need to define appropriate parameters in order to describe the quality

Reliable measurements of vertical profiles of wind speed and direction are needed for testing models and methodologies of use for wind energy assessment. In particular, modelling complex terrain such as coastal areas is challenging due to the coastal discontinuity that is not accurately resolved in mesoscale numerical model. Here, we present a unique database from a coastal site in South Italy (middle of the Mediterranean area) where vertical profiles of wind speed and direction have been collected during a two-year period from a wind-lidar ZEPHIR-300® at a coastal-suburban area. We show an overview analysis on two-year 10-minute averaged wind profiles.

[EN] A study on the sources of variability in the measurement of particle size distribution using a two-stage dilution system and an engine exhaust particle sizer was conducted to obtain a comprehensive and repeatable methodology that can be used to measure the particle size distribution of aerosols emitted by a light-duty diesel engine under transient operating conditions. The paper includes three experimental phases: an experimental validation of the measurement method; an evaluation of the influence of sampling factors, such as dilution system pre-conditioning; and a study of the effects of the dilution conditions, such as the dilution ratio and the dilution air temperature. An examination of the type and degree of influence of each studied factor is presented, recommendations for reducing variability are given and critical parameter values are identified to develop a highly reliable measurement methodology that could be applied to further studies on the effect of engine operating parameters on exhaust particle size distributions. © 2011 IOP Publishing Ltd.

The correct analysis of amorphous silica concentration (CASi) in natural waters is crucial if one wants to correctly quantify terrestrial and/or riverine ASi fluxes. Soil ASi measurements are conducted with a constant solid to solution ratio (). As the suspended particulate matter concentration (CSPM), and therefore, cannot be exactly known a priori in river samples. It is important to understand how variations in effect analysed CASi. The objectives of this paper are (i) to investigate whether and how variations in values affect measured CASi in river runoff samples and (ii) to investigate whether or not it is possible to define a range of within which CASi in runoff and/or soil samples can be accurately measured. For the laboratory experiment 30 runoff samples with a wide range of CSPM, typical for the Belgian Loam Belt, were prepared and analysed using the alkaline digestion method (0.1M Na2CO3). Our study confirmed that the alkaline digestion method proposed by DeMaster can be used for runoff samples provided that is within certain limits: at very low (<0.1kgm-3), subsample heterogeneity results in high variability of measured CASi while at higher values (>0.8kgm-3) incomplete dissolution of ASi as well as the reduction of mineral dissolution rates results in underestimated CASi. As both errors compensate one another, the range of applicable -values can be extended above the theoretically correct limit (1.6kgm-3). The finding that reliable measurements can be made within a relatively wide range of values (0.1≤≤1.6kgm-3) is important. It is now possible to propose a method for the measurement of ASi in runoff samples. We make recommendations for ASi analysis distinguishing samples with a low and high CSPM. For samples with a low CSPM (≤1.6kgm-3) the standard procedure is proposed while for samples with a high CSPM (>1.6kgm-3) an adapted procedure is proposed, analogue to that for soil samples. However, one should be aware that the range and limits for pr

Light-matter interaction can be greatly enhanced in nano-scale plasmonic cavities with tightly confined optical mode, where the mode volume determines the interaction strength. The experimental determination of the mode volume of plasmonic elements is therefore of fundamental importance. Mapping the electric field distribution using near-field scanning optical microscopy (NSOM) may disturb the field distribution hence prevent a reliable measurement of the mode volume. Here, we develop a non-pertubative technique to experimentally determine the mode volume of plasmonic resonators in the far field through a unique optical force method.