Henrik Mäntynen

Use of the predictable quantum efficient detector with light sources of uncontrolled state of polarization

Analysis of the reflectance losses of the predictable quantum efficient detector (PQED) operated at room temperature is presented. An efficient method of using the ratio of photocurrents from the two photodiodes of the PQED is developed to determine the reflectance losses without direct measurement of the reflectance for an unknown state of polarization of the incident light. A detailed analysis is presented to estimate the associated reflectance losses for detectors with either seven or nine internal reflections. For the 7-reflection PQED, the relative standard uncertainty component of spectral responsivity due to reflectance loss correction can be reduced mostly below 100?ppm with the photocurrent ratio measurement whereas for the 9-reflection PQED the uncertainties remain below 20?ppm in the wavelength range from 400 to 900?nm with an uncontrolled polarization state of the incident light.

Double-coiled tungsten filament lamps as absolute spectral irradiance reference sources

We have developed a physical model for the spectral behaviour of the radiation of tungsten filament lamps. The model is based on Plancks radiation law, published values for the emissivity of tungsten, measurement geometry and measured values for a residual correction function. In this paper, we study the physical interpretation of the model. The studied properties influencing the lamp spectra include the emissivity data used, light recycling effect due to the cylindrical shape of the filament, transmittance of the glass envelope and the halogen gas and temperature dependence of the transmittance. It appears that in addition to tungsten emissivity, one needs to account for the bulb transmittance and the light recycling within the cylindrical filament. We did not observe any wavelength dependence of the absorption of the filling gas.

Measurement of Nanowire Optical Modes Using Cross-Polarization Microscopy

A method to detect optical modes from vertical InGaAs nanowires (NWs) using cross-polarization microscopy is presented. Light scattered from the optical modes in the NWs is detected by filtering out the polarized direct reflection with a crossed polarizer. A spectral peak and a valley were seen to red-shift with increasing NW diameter in the measured spectra. The peak was assigned to scattering from the TE01 optical mode and the valley was an indication of the HE11 mode, based on finite-element and scattering matrix method simulations. The cross-polarization method can be used to experimentally determine the spectral positions of the TE01 and HE11 optical modes. The modes are significantly more visible in comparison to conventional reflectance measurements. The method can be beneficial in the characterization of NW solar cells, light-emitting diodes and lasers where precise mode control is required.

Gonioreflectometric properties of metal surfaces

Angularly resolved measurements of scattered light from surfaces can provide useful information in various fields of research and industry, such as computer graphics, satellite based Earth observation etc. In practice, empirical or physics-based models are needed to interpolate the measurement results, because a thorough characterization of the surfaces under all relevant conditions may not be feasible. In this work, plain and anodized metal samples were prepared and measured optically for bidirectional reflectance distribution function (BRDF) and mechanically for surface roughness. Two models for BRDF (Torrance?Sparrow model and a polarimetric BRDF model) were fitted to the measured values. A better fit was obtained for plain metal surfaces than for anodized surfaces.

Characterization of thin-film thickness

Analysis methods and instrumentation for obtaining optical parameters and thickness profiles of thin-film samples from spectrophotometric and ellipsometric measurements are presented. Measured samples include thermally grown and evaporated SiO2 on a silicon substrate and a polymer photoresist layer on silicon. Experimental results at multiple sample positions give the thickness uniformity and optical constants of thin films. The thickness results obtained with spectrophotometry and ellipsometry agree within 1 nm for the 300 nm thick layer of SiO2 on silicon. For the 1600 nm thick resist sample the agreement of the measurement methods is within 8 nm. For the sample with a nominally 6000 nm thick layer of SiO2 on silicon, there is a deviation of ~100 nm between the spectrophotometry and ellipsometry results. As an application, the optical parameters of a SiO2 layer on an induced junction silicon photodiode are determined by spectrophotometry and are used to confirm earlier values and uncertainties of the SiO2 refractive index and layer thickness non-uniformity.

Toward SI Traceability of a Monte Carlo Radiative Transfer Model in the Visible Range

A 3-D Monte Carlo (MC) ray-tracing radiative transfer model is tested for its ability to simulate the bidirectional reflectance factors (BRFs) of a grooved artificial target given SI-traceable measurements of the optical and topographic properties of the target’s surface. The optical properties of a grooved target and an identical flat target were measured with the goniospectrophotometer at the National Metrology Institute of U.K. (NPL) and are traceable to the NPL scales of radiance factor. The topographic measurements were performed with the coordinate measuring machine at the National Metrology Institute of Finland (MIKES), and are traceable to the realization of the meter. The BRFs of the flat target were used to parameterize analytical scattering functions for rough surfaces. Similarly, the topographic measurement results were used to construct a structural model of the grooved target. Each element within this structural model then had its optical properties defined by the parameterized scattering function before the 3-D MC model simulated the BRFs of the grooved target under well-defined illumination and viewing conditions. The measured and modeled BRFs agreed for 72% of the measured geometries in the plane of incidence within the measurement and modeling uncertainties. The relative root-mean-squared (RMSE) error was 0.19. In the plane orthogonal to the plane of incidence, the measured and modeled BRFs agreed for 45% of the measured geometries, and the relative RMSE between measured and modeled values was 0.65.