Maksim Shpak

Non-Reflecting Silicon and Polymer Surfaces by Plasma Etching and Replication

Constantly increasing demand of renewable and nonpolluting energy production methods has made solar cells one of today’s hottest research areas. Developing more cost-effective fabrication methods that enable production of extremely non-refl ecting surfaces is one of the key issues in solar cell research. [ 1 , 2 ] Many other applications, such as miniaturized chemical analysis systems, would also benefi t greatly from low-cost surfaces with low and uniform refl ectivity. [ 3 ] Typically, suppression of Fresnel refl ection has been achieved by antirefl ective coatings, but they suppress refl ection effi ciently only in a narrow wavelength range. Suppression of refl ection over a broad spectral range can be achieved by using nanotextured surfaces that form a graded transition of the refractive index from air to the substrate. [ 1 , 2 , 4–12 ]

Mathematical limitations of the CIE mesopic photometry system

The International Commission on Illumination (CIE) has published a recommended system for mesopic photometry based on visual performance. The system provides means for determining mesopic photometric values based on measuring the spectral composition and intensity of light. The system uses an iterative calculation method. We investigate the conditions under which this system is applicable and identify potential problems with the iterative method. We show that the system works well for the vast majority of lighting applications. However, it has non-convergence and discontinuity issues for sources with very high and very low values of scotopic-photopic ratio. A set of parameterised formulae is presented that approximates the mesopic model and provides a continuous, closed-form solution for the adaptation level in all lighting conditions.

Out-of-Range Stray Light Characterization of Single-Monochromator Brewer Spectrophotometers

ABSTRACT Stray light in single-monochromator Brewer instruments increases the uncertainty of solar ultraviolet spectral irradiance measurements and ozone retrievals. To study how spectral irradiance within and outside the measurement ranges of the instruments affects stray light, two Brewer MKII instruments were characterized for the level of in- and out-of-range stray light at multiple laser wavelengths. In addition, several solar-blind filters utilized in single-monochromator Brewers to limit out-of-range stray light were characterized for spectral and spatial transmittances. Finally, the measurement results were used to simulate the effect of stray light and stray light correction on spectral irradiance and ozone measurements at different wavelength regions. The effect of stray light from wavelengths above 340 nm was found to be negligible compared with other sources of uncertainty. On the other hand, contributions from wavelengths between 325 and 340 nm can form a significant portion of the overall stray light of the instrument, with 325 nm being the upper limit of the nominal measurement range of the instrument.

Luminance meter for photopic and scotopic measurements in the mesopic range

This paper presents a design and realization of a dual-channel luminance meter for simultaneous measurement of luminance with photopic and scotopic weightings. Such measurements are useful in mesopic conditions, i.e. when the luminance is in the range of 0.005–5 cd m−2. The instrument is a spot luminance meter with two spectrally weighted channels. The collected light is detected with silicon detectors and a computer-controlled dual-channel switched-integration amplifier. The instrument is characterized for relative spectral responsivity against a calibrated spectroradiometer using a radiance source based on an integrating sphere with input from a monochromator. An absolute luminance responsivity calibration is made against a sphere-based luminance standard at a level close to the high end of the mesopic range. The standard uncertainty in luminance responsivity calibration is 0.3% for the photopic channel and 0.6% for the scotopic channel. In addition, characterization measurements were carried out for the instruments linearity, stray light sensitivity and polarization dependence. The results show very good noise performance, allowing fast measurements over the whole mesopic range. The noise equivalent power was measured to be approximately 20 fW Hz−1/2, equal to a noise equivalent luminance of 30 µcd m−2 Hz−1/2. Estimated uncertainty of measurements for typical light sources is 2.2% (k = 2) at the lowest luminance levels of the mesopic range.

Optical temperature measurements of silicon microbridge emitters

Microbridges are miniature suspended structures fabricated in silicon. Passing a current through the microbridge can heat it up to the point of incandescence. A glowing microbridge can be used as a wideband light source. This study presents a method for optical measurement of the temperature of a microbridge. Spectroscopic measurements of microbridges are optically challenging, because the multilayer structures cause interference effects. To determine the temperature from the emitted spectrum, the emissivity was modeled with thin-film Fresnel equations. Temperatures of 500-1100 degrees C were obtained from the measured spectra at different levels of applied power. The range is limited by the sensitivity of the detectors at lower power levels and by the stability of the bridge at higher levels. Results of the optical measurements were compared with contact temperature measurements made with a microthermocouple in the same temperature range. The results of the two methods agree within 100 K.