Single Reflection Measurement Research Articles

Measuring the Optical Properties of Highly Diffuse Materials.

Measuring the optical properties of highly diffuse materials is a challenge as it could be related to the white colour or an oversaturation of pixels in the acquisition system. We used a spatially resolved method and adapted a nonlinear trust-region algorithm to the fit Farrell diffusion theory model. We established an inversion method to estimate two optical properties of a material through a single reflectance measurement: the absorption and the reduced scattering coefficient. We demonstrate the validity of our method by comparing results obtained on milk samples, with a good fitting and a retrieval of linear correlations with the fat content, given by R2 scores over 0.94 with low p-values. The values of absorption coefficients retrieved vary between 1 × 10-3 and 8 × 10-3 mm-1, whilst the values of the scattering coefficients obtained from our method are between 3 and 8 mm-1 depending on the percentage of fat in the milk sample, and under the assumption of the anisotropy factor g>0.8. We also measured and analyzed the results on white paint and paper, although the paper results were difficult to relate to indicators. Thus, the method designed works for highly diffuse isotropic materials.

Reflection measurements to reveal the absorption in nanowire arrays

The absorption of light is at the core of photovoltaic applications. For many nanostructure-based devices, an assessment of the absorption in the nanostructures is complicated by a thick, opaque substrate that prohibits transmission measurements. Here, we show how a single reflection measurement can be used for approximating the amount of light absorbed in vertical semiconductor nanowire arrays.

Optimization of Azimuthal Scan Procedure for Absolute Structure Determination

The paper describes the application of the azimuthal scan technique for absolute structure determination using X-ray anomalous dispersion. A diffraction pattern with rotation around the scattering vector provides information about various anisotropic effects: absorption, extinction and multi-beam interaction. Recording of azimuthal scans for Friedel pairs is proposed as an alternative to single reflection measurement. Several factors affecting the smoothness of the azimuthal scan curves are discussed and a procedure for eliminating various sources of errors, involving a Fourier filtering, is proposed in order to increase feasibility of chiral discrimination.

Dielectric Fabry–Pérot interferometer for temperature dependent far-infrared reflectivity measurements of heavy-fermion metals in high magnetic fields

A far-infrared reflectivity set up has been developed for spectroscopy on highly reflective materials in a 20 T-class resistive Bitter magnet. As a first application, far-infrared reflectivity measurements on the heavy-fermion compound URu2Si2 have been performed using a silicon reflection Fabry–Pérot interferometer as a multiple reflection device. In a resonance, this Fabry–Pérot technique is one order of magnitude more sensitive than a single reflection measurement. Changes in the reflectivity as a function of magnetic field are resolved with an accuracy of 0.2% and the absolute value of the reflectivity can be obtained with an accuracy of 0.5%. With this interferometer, an excitation at about 40 cm−1 in the heavy-fermion system URu2Si2 is investigated at temperatures between 2 and 20 Kelvin and in magnetic fields up to 20 T. The excitation appears to extend to lower energies under influence of a large magnetic field.

Grating Light Reflection Spectroscopy for Determination of Bulk Refractive Index and Absorbance

An optical sensing technique is described and evaluated for sensitivity to changes in refractive index and absorbance of model sample matrices. A binary dielectric/metal transmission diffraction grating is placed in contact with a sample and utilized in reflection mode; thus, the light captured and analyzed does not pass through the sample. This particular condition creates thresholds at which a particular transmitted diffraction order is transformed from a traveling wave to an evanescent one. The positions of these thresholds depend upon the complex dielectric function of the sample, the period of the grating, and the wavelength and incident angle of light striking the grating. Experimental evidence directly supports the theoretical predictions regarding responses to both the real and imaginary portions of the refractive index: the reflection coefficient derivative wavelength peak position shifts linearly with changes in the real part of the refractive index, and the derivative peak amplitudes exhibit a square-root dependence on absorbance. Refractive index sensitivity to a series of ethanol/water solutions is demonstrated with detectable changes in index as small as 2 × 10(-)(6). Absorbance sensitivity is shown via the differentiation of methylene blue samples having equivalent 1 cm path length absorbances between 0.459 and 244 AU. In a single reflection measurement, GLRS offers a large dynamic range for absorbance detection, allows simultaneous determination of bulk refractive index in optically dense media, and provides a platform for performing continuous process analysis.

Determination of the optical constants and thickness of thin films on slightly absorbing substrates

A method for solving the optical constants of a thin film on a slightly absorbing substrate is proposed. Using only a single-reflectance measurement together with the interference fringes, one can calculate with good accuracy the thickness and the real and imaginary parts of the refractive index of the film. Besides its simplicity, this method also avoids the problem of multiple solutions. We show that this technique is effective in solving for the optical constants of thin films with weak or moderate absorption characteristics, and in particular we applied it to obtain the optical properties of amorphous C thin films on Si.

Supermirrors study by neutron multireflection

We present here time of flight neutron multireflection measurements. This technique has been developed at the Laboratoire Leon Brillouin (Saclay-France). Used in the investigation of supermirrors NiC/Ti, it allows us to increase the precision of the measurement of the most important part of the curve for technological applications: the extension of the total reflection plateau. The results on three systems ( 58 Ni single layer, multilayer NiC/Ti, supermirror NiC/Ti) are presented in this paper. Beyond the good quality of the mirrors, they demonstrate the very good reliability of such a measurement. Moreover, they show that compared to a classical single reflection measurement, multireflection experiment enables us to increase the accuracy of the reflectivity value measured on the extended plateau

Automated reading of the multipoint inoculated antibiotic sensitivity test

A television-computer system is described which scans sets of macro-colonies on agar plates to determine sensitivity of bacteria to selected antibiotics. Decisions are based on a single reflectance measurement within the macro-colony. Results are given of a comparative trial between the machine and six experienced human observers. No significant difference of performance was found, and the machine offers advantages when performing large numbers of tests.