Biomedical subjects

Erkki Ikonen

Publications and source records attributed to Erkki Ikonen.

3 recordsLinked to original sources

PubMed2006

Characterization of thin films based on reflectance and transmittance measurements at oblique angles of incidence.

The optical parameters of a SiO2 thin-film coating determined from the spectral reflectance and transmittance measurements at various incidence angles, including the normal incidence and the Brewster's angle, are compared in this paper. The high-accuracy measurements were carried out through visible-near-infrared spectral regions by using our purpose-built instruments. The optical parameters obtained from the reflectance and the transmittance data are consistent over the angles of incidence and agree within 0.2%. The effect of important systematic factors in the oblique-incidence spectrophotometric measurements is also discussed.

Journal Article↗

PubMed2005

Determination of the diffuser reference plane for accurate illuminance responsivity calibrations.

It is difficult to predict where the effective measurement plane is situated with dome-shaped diffusers often used in commercial photometers and radiometers. Insufficient knowledge of this plane could lead to large systematic errors in calibration of the illuminance responsivity of photometers. We propose a method that can be used to determine this reference plane accurately, based on the inverse-square law between the measured signal and the distance from the source. The method is demonstrated with three commercial photometers with dome-shaped diffusers of different geometries. By taking into account the measured shifts of the reference planes (5.0 +/- 0.5 mm, 7.8 +/- 0.3 mm, and 8.5 +/- 0.7 mm), we reduced the systematic measurement errors up to 2% to statistical uncertainty components at the level of 0.2%.

Journal Article↗

PubMed2004

Gonioreflectometer for measuring spectral diffuse reflectance.

Gonioreflectometric determination of reflectance factors that involves hemispherical collection of reflected flux, which is an alternative to integrating sphere-based methods, is discussed. A detailed description of a gonioreflectometer built at the Helsinki University of Technology is presented. The instrument is used to establish an absolute scale of total diffuse reflectance factors throughout the spectral range 360-830 nm. The hemispherical reflectance factors are obtained through integration of the gonioreflectometric measurement results. The reflectance factors of white high-quality artifacts can be determined with a combined standard uncertainty of 0.20%. Results of test measurements were found to be in agreement with values traceable to other absolute scales based on integrating-sphere methods.

Journal Article↗