Browsing by Department "Metrology Research Institute"
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Item Calibration of Near-Infrared Detectors Using a Wavelength Tunable Light Source(Springer-Verlag GmbH and Co. KG, 2020-04-01) Maham, Kinza; Vaskuri, Anna; Manoocheri, Farshid; Ikonen, Erkki; Metrology Research Institute; Dept Signal Process and AcoustThis paper presents the spectral responsivity calibrations of two indium gallium arsenide (InGaAs) and one germanium based near-infrared photovoltaic detectors using a wavelength tunable laser source based on a supercontinuum laser developed at the Metrology Research Institute, Aalto University. The setup consists of a supercontinuum laser based on a photonic crystal fiber as the light source, a laser line tunable filter, and coupling optics. These responsivity calibrations are performed against a pyroelectric radiometer over a wide spectral range of 800–2000 nm. Our wavelength tunable laser source has a high spectral power up to 2.5 mW with a narrow spectral full-width-at-half-maximum of 3 nm at a wavelength of 1100 nm. Despite the sharp spectral intensity variations, no artifacts are observed in the spectral responsivities of the detectors. Comparison of the spectral responsivities of the InGaAs detectors measured using the wavelength tunable laser and the earlier calibrations performed at the Metrology Research Institute in 2010 and 2016, shows that the higher spectral power of wavelength tunable light source decreases the expanded uncertainty from approximately 4% to 2.2–2.6% over the spectral range of 820–1600 nm. Temperature dependence of the spectral responsivities near the band gap edges are also measured and analysed.Item Cantilever-based photoacoustic sensor for terahertz range(SPIE, 2023) Ikonen, Erkki; Sharma, Sucheta; Ahmadi, Mohsen; Rossi, Jussi; Vainio, Markku; Sun, Zhipei; Steiger, Andreas; Metrology Research Institute; Centre of Excellence in Quantum Technology, QTF; Tampere University; University of Helsinki; Department of Electronics and Nanoengineering; Physikalisch-Technische Bundesanstalt; Department of Information and Communications EngineeringAdvantages of photoacoustic detection with a silicon cantilever microphone are demonstrated in the THz range. In our method, earlier membrane microphone is replaced with robust silicon cantilever microphone, which can tolerate high intensity of the input radiation in contrast to vulnerable membrane. The responsivity of the photoacoustic sensor was confirmed to be constant over almost six orders of magnitude of input power, which is not easy to achieve with any other detector of THz radiation. Another favorable feature of the photoacoustic sensor is its uniform spatial responsivity over areas of several millimeters in size. Finally, we measured nearly constant spectral responsivity of the photoacoustic sensor for the wavelength range of 0.3 µm to 200 µm.Item Cantilever-enhanced photoacoustic measurement of light-absorbing aerosols(TAYLOR & FRANCIS, 2021) Karhu, Juho; Kuula, Joel; Virkkula, Aki; Timonen, Hilkka; Vainio, Markku; Hieta, Tuomas; Metrology Research Institute; Finnish Meteorological Institute; University of Helsinki; Gasera Ltd.Photoacoustic detection is a sensitive method for measurement of light-absorbing particles directly in the aerosol phase. In this article, we demonstrate a new sensitive technique for photoacoustic aerosol absorption measurements using a cantilever microphone for the detection of the photoacoustic signal. Compared to conventional diaphragm microphones, a cantilever offers increased sensitivity by up to two orders of magnitude. The measurement setup uses a photoacoustic cell from Gasera PA201 gas measurement system, which we have adapted for aerosol measurements. Here we reached a noise level of 0.013 Mm−1 (one standard deviation) with a sampling time of 20 s, using a simple single-pass design without a need for a resonant acoustic cell. The sampling time includes 10 s signal averaging time and 10 s sample exchange, since the photoacoustic cell is designed for closed cell operation. We demonstrate the method in measurements of size-selected nigrosin particles and ambient black carbon. Due to the exceptional sensitivity, the technique shows great potential for applications where low detection limits are required, for example size-selected absorption measurements and black carbon detection in ultra clean environments.Item Characterization of PillarHall test chip structures using a reflectometry technique(Institute of Physics Publishing, 2023-09) Danilenko, Aleksandr; Rastgou, Masoud; Manoocheri, Farshid; Kinnunen, Jussi; Korpelainen, Virpi; Lassila, Antti; Ikonen, Erkki; Metrology Research Institute; Chipmetrics Ltd; VTT Technical Research Centre of Finland; Department of Information and Communications EngineeringThin film samples where one of the thin layers consists of a vacuum or air are called PillarHalls due to their support structure in silicon wafers. Custom PillarHall samples were provided by Chipmetrics Ltd and characterized by reflectometry with a Cary 7000 spectrometer. Data at 8° of angle of incidence were collected with p-polarization of the incident light within the wavelength range of 550-1800 nm. These data were then analyzed with a dedicated MATLAB code, using fitting software accompanying the transfer matrix method for calculation of the reflectance spectrum. Layer thicknesses and unknown refractive indices were chosen as fitted parameters. The oscillating reflectance spectrum of the PillarHall test chip yielded an air gap thickness of 86 nm with an estimated standard uncertainty of 5 nm. This is close to the nominal value of 100 nm. The results demonstrate that reflectometry data are sensitive to the thickness of the thin air layer deep inside the silicon structure.Item Characterization of predictable quantum efficient detector at 488 nm and 785 nm wavelengths with an order of magnitude change of incident optical power(IOP Publishing Ltd., 2022-01) Korpusenko, Mikhail; Manoocheri, Farshid; Kilpi, Olli Pekka; Varpula, Aapo; Kainlauri, Markku; Vehmas, Tapani; Prunnila, Mika; Ikonen, Erkki; Metrology Research Institute; VTT Technical Research Centre of FinlandWe investigate the predictable quantum efficient detector (PQED) in the visible and near-infrared wavelength range. The PQED consists of two n-type induced junction photodiodes with Al2O3 entrance window. Measurements are performed at the wavelengths of 488 nm and 785 nm with incident power levels ranging from 100 μW to 1000 μW. A new way of presenting the normalized photocurrents on a logarithmic scale as a function of bias voltage reveals two distinct negative slope regions and allows direct comparison of charge carrier losses at different wavelengths. The comparison indicates mechanisms that can be understood on the basis of different penetration depths at different wavelengths (0.77 μm at 488 nm and 10.2 μm at 785 nm). The difference in the penetration depths leads also to larger difference in the charge-carrier losses at low bias voltages than at high voltages due to the voltage dependence of the depletion region.Item Characterization of predictable quantum efficient detector in terms of optical non-linearity in the visible to near-infrared range(IOP Publishing Ltd., 2021-10) Tanabe, Minoru; Shitomi, Hiroshi; Dönsberg, Timo; Ikonen, Erkki; National Institute of Advanced Industrial Science and Technology; VTT Technical Research Centre of Finland; Metrology Research InstituteThe characteristics of a predictable quantum efficient detector (PQED) in terms of optical non-linearity in the visible to near-infrared range were investigated under zero-bias and reverse-bias voltage conditions. In the zero-bias condition, linear behavior was observed in the wavelength from 405 nm to 1060 nm in the photocurrent range of 1 nA to 10 mu A, and saturation occurred for photocurrents over 10 mu A for all wavelengths. In the reverse-bias voltage of 10 V, the linear behavior was observed in the photocurrent range of 64 nA to 1 mA except for the wavelength of 1060 nm, and the saturation photocurrent increased up to 1 mA. The supralinearity value at 1060 nm increased sharply from the photocurrent of 100 mu A, and its maximum value reached up to 0.34% at the photocurrent of 1 mA because of the back surface recombination and the longer absorption length. The spectral linearity results of the PQED help us to understand the charge-carrier loss mechanism in the PQED, and would lead to more accurate optical measurement with it.Item Cryostat setup for measuring spectral and electrical properties of light-emitting diodes at junction temperatures from 81 K to 297 K(AMER INST PHYSICS, 2020-01-01) Martikainen, Elvira; Vaskuri, Anna; Dönsberg, Timo; Ikonen, Erkki; Metrology Research Institute; Dept Signal Process and AcoustWe introduce a cryostat setup for measuring fundamental optical and electrical properties of light-emitting diodes (LEDs). With the setup, the cryostat pressure and the LED properties of the forward voltage, junction temperature, and electroluminescence spectrum are monitored with temperature steps less than 1.5 K, over the junction temperature range of 81-297 K. We applied the setup to commercial yellow AlGaInP and blue InGaN LEDs. At cryogenic temperatures, the fine structure of the electroluminescence spectra became resolved. For the yellow LED, we observed the phonon replica at 2.094 eV that was located 87 meV below the peak energy at the junction temperature of 81 K. For the blue LED, we observed the cascade phonon replicas at 2.599 eV, 2.510 eV, and 2.422 eV with the energy interval of 89 meV. For both LED types, the forward voltage increased sharply toward the lower temperatures due to the increased resistivity of materials in the LED components. We found significant differences between the temperaturedependent behaviors of the forward voltages, spectral peak energies, and bandgap energies of LEDs obtained from the Varshni formula. We also noted a sharp pressure peak at 180-185 K arising from the solid-vapor phase transition of water when the base level of the cryostat pressure was approximately 0.4 mPa.Item Determining the shape of reflectance reference samples for curved surface reflectors(IOP Publishing Ltd., 2020-05) Lanevski, Dmitri; Manoocheri, Farshid; Vaskuri, Anna; Hameury, Jacques; Kersting, Robert; Monte, Christian; Adibekyan, Albert; Kononogova, Elena; Ikonen, Erkki; Metrology Research Institute; Laboratoire national de métrologie et d'essais; Fraunhofer Institute for Production Systems and Design Technology; Physikalisch-Technische BundesanstaltFoils made of different materials are often used as reflective insulators. Many manufacturers aim to accurately measure their optical properties to estimate and improve their performance. However, flat reflectance reference samples used in measurements do not correctly represent reflective insulators and cause discrepancies between different measurement techniques. The current work presents a method for modelling surface shape of appropriate reflectance reference samples that could be produced by additive manufacturing. The method is based on studying the reflection distribution of reflective insulators and is described with an example of aluminium foil. The method's performance is validated using Monte-Carlo simulations.Item Digital implementations for determination of temporal light artefacts of LED luminaires(SAGE Publications, 2023-11-29) Mantela, V.; Nordlund, R.; Askola, J.; Kärhä, P.; Ikonen, E.; Metrology Research Institute; Dept Signal Process and Acoust; Department of Information and Communications EngineeringFlicker and stroboscopic effects caused by a temporally modulated light source may be harmful for the human visual system. Standardized measurement methods have been developed for the related temporal light artefacts of LED luminaires. It was found out that the performance of the International Electrotechnical Commission (IEC) recommended flickermeter implementation is highly dependent on sampling frequency. Novel digital implementations for the flickermeter and stroboscopic effect visibility measure (SVM) were created to remove any inaccuracies. The performance of the novel Aalto implementations does not depend on the sampling frequency when running the test waveforms of the IEC standard through the implementations. As compared with the IEC recommended digital implementations, Aalto flickermeter decreases the average error related to the test waveforms from −0.05 to +0.003, and Aalto SVM meter also decreases the average error by almost two orders of magnitude.Item Electromagnetic radiation detection using cantilever-based photoacoustic effect: A method for realizing power detectors with broad spectral sensitivity and large dynamic range(Elsevier, 2022-04-16) Sharma, Sucheta; Laurila, Toni; Rossi, Jussi; Uotila, Juho; Vainio, Markku; Manoocheri, Farshid; Ikonen, Erkki; Metrology Research Institute; Tampere University; Patria AviationA sensitive photoacoustic detection approach employing a silicon cantilever is investigated for power measurement of electromagnetic radiation. The technique which is actuated by pressure waves generated through radiation-induced heat depicts high sensitivity for a considerably large spectral range from 325 nm to 1523 nm. The implemented method shows linear response in the measurement of radiation power from 15 nW to 6 mW demonstrating a dynamic range of almost six orders of magnitude. A numerical model has been developed to analyze and optimize the measurement sensitivity. The model allows studying different dimensions of the cantilever which is one of the key components of the radiation detection process. The numerical results are in good agreement with experimental results. The electromagnetic power detection technique shows future potential for industrial applications and scientific studies.Item General V(λ) mismatch index: History, current state and new ideas(SAGE PUBLICATIONS, 2023-06-01) Krüger, U.; Ferrero, A.; Thorseth, A.; Mantela, V.; Sperling, A.; TechnoTeam Bildverarbeitung GmbH; Consejo Superior de Investigaciones Cientificas (CSIC); Technical University of Denmark; Metrology Research Institute; Physikalisch-Technische Bundesanstalt; Department of Information and Communications EngineeringThe general V(λ) mismatch index f1′ specifies the mismatch between the relative spectral responsivity of a photometer, and the spectral luminous efficiency function for photopic vision, V(λ). A short review of its historical development explains the reasons for the current definition and which adjustments may be helpful in the future. The properties of the current definition are described in detail. It is very likely that photometers will be calibrated with a white light-emitting diode (LED) light source as the reference in the future. This might involve the need for a more appropriate definition of the general V(λ) mismatch index, either by using a different normalisation in f1′ for the relative spectral responsivity of the photometer or by introducing a different type of function for assessing the mismatch. On the other hand, the measurement of coloured LEDs is also becoming increasingly important. So, is a single general mismatch index for white and coloured light sources sufficient?Item High-resolution setup for measuring wavelength sensitivity of photoyellowing of translucent materials(2015) Vaskuri, Anna; Karha, Petri; Heikkila, Anu; Ikonen, Erkki; Metrology Research InstituteItem Impact ionization in silicon at low charge-carrier energies(American Institute of Physics, 2023-08-01) Korpusenko, Mikhail; Vaskuri, Anna; Manoocheri, Farshid; Ikonen, Erkki; Metrology Research Institute; Department of Information and Communications EngineeringPhotons absorbed in silicon produce electron-hole pairs, which can cause impact ionization and quantum yield larger than one. Reliable determination of quantum yield at low charge-carrier energies (<4 eV) has been challenging because photon losses due to reflectance and charge-carrier losses due to recombination affect the resulting photocurrent. Here, we present how the measurement of this fundamental characteristic of silicon crystals can be improved in the charge-carrier energy range of 1.6-4 eV by using a predictable quantum efficient detector based on induced junction photodiodes optimized for photon-to-electron conversion efficiency. The measured quantum yield values are compared with the results of theoretical calculations, revealing increased impact-ionization probabilities at 2.25 and 3.23 eV on the top of a smooth background curve calculated by a model based on free charge carriers in the silicon lattice. For the results at the lowest energies, both data and an asymptotic extrapolation model suggestthat quantum yield exceeds unity by ∼10−4 at 1.6 eV corresponding to a photon wavelength of 450 nm.Item Increased detector response in optical overfilled measurements due to gas lens formation by nitrogen flow through the entrance aperture(IOP Publishing Ltd., 2021-10) Askola, J.; Maham, K.; Kärhä, Petri; Ikonen, E.; Dept Signal Process and Acoust; Metrology Research InstituteAccording to our experimental results, a nitrogen flow used to prevent dust and moisture entering a detector may influence measurements performed with trap detectors in overfilled conditions. A stable light source was measured with a wedged trap detector with 4 mm aperture, and the nitrogen flow rate was varied. The nitrogen flow was found to have the largest effect of up to 0.8% on the responsivity of the detector at around 1.0 l min(-1) flow rate. The effect of nitrogen flow can be removed down to 0.02% by an added crossflow which removes the nitrogen out of the optical axis. In another experiment, the effect was removed almost completely by changing the flowing gas from nitrogen to synthetic dry air. We also present measurement results that indicate the responsivity changes with nitrogen to be smaller than 0.05% with underfilled beam geometry, even without the added crossflow. Based on simulations, the nitrogen flow through the detector forms a gradient-index type gas lens in front of the detector increasing the effective aperture area and thus the responsivity. In the underfilled measurement geometry there is no light close to the aperture edge which could be refracted inside the detector. Finally, we consider methods to ensure that the responsivity changes due to the gas flow remain below 0.05% in overfilled measurement geometry, without compromising the cleanliness of the detector with too small gas flow rate.Item Influence of smart lighting control on the lifetime of high power LED luminaires(Institute of Physics Publishing, 2019-01-01) Askola, Janne; Baumgartner, Hans; Pulli, Tomi; Kärhä, Petri; Ikonen, Erkki; Metrology Research Institute; Dept Signal Process and AcoustLED lighting and smart controlling can decrease the consumption of electric power in zero or positive energy buildings. This study demonstrates that cyclic dimming, which appears in smart controlling, e.g. through occupancy sensing, might have an effect on the luminaire lifetimes and failure rates. Two different types of LED luminaires were aged in 30-s cycled dimming and undimmed modes. The manufacturer-specified lifetimes for both luminaire types were 100 000 hours. For one of the luminaire types, four out of five cycled units failed before 30 000 operating hours. For the uncycled luminaires, the lifetimes estimated from the measurements were over 100 000 hours. For the other type, the estimated lifetimes were 75 000 hours and 64 000 hours for uncycled and cycled luminaires, respectively.Item Luminous intensity comparison based on new standard lamps with LED reference spectrum(2019) Gerloff, Thorsten; Kallenbach, Laura; Ledig, Johannes; Schrader, Christian; Sperling, Armin; Pulli, Tomi; Askola, Janne; Smid, Marek; Kliment, Petr; Pons, Alicia; Ferrero, Alejandro; Gal, Peter; Brida, Giorgio; Blattner, Peter; Stuker, Florian; Schneider, Markus; Dönsberg, Timo; Poikonen, Tuomas; Physikalisch-Technische Bundesanstalt; Metrology Research Institute; Dept Signal Process and Acoust; Czech Metrology Institute; CSIC; MKEH; Istituto Nazionale di Ricerca Metrologica INRIM; Federal Institute of Metrology (METAS); Osram GmbH; VTT Technical Research Centre of FinlandItem Machine-readable universal data format for bidirectional reflectance distribution function and BiRDview—An open-source web-based application for viewing and comparing bidirectional reflectance data(JOHN WILEY & SONS, 2022-10) Lanevski, Dmitri; Ferrero, Alejandro; Perales, Esther; Manoocheri, Farshid; Ikonen, Erkki; Metrology Research Institute; CSIC; University of AlicanteModern studies of bidirectional reflectance distribution function (BRDF) and its applications using data and machine-driven science require formatting of BRDF data according to Findable, accessible, interoperable and reusable (FAIR) data principles. As a solution a FAIR universal BRDF file-format based on Java Script Object Notation (JSON) is proposed. JSON principles as well as file structure are explained and examples are given. Automatic validation of universal BRDF file format is realized with the help of JSON schema. Furthermore, the source code and accompanying documentation are presented in dedicated supporting material files. It is expected that after its wide adoption, the proposed BRDF file format will enhance collaboration between different research groups and benefit machine-driven science. The uptake is facilitated by introducing a BiRDview—a modern open-source web-based application for BRDF visualization.Item Modeling the spectral shape of InGaAlP-based red light-emitting diodes(2015) Vaskuri, Anna; Baumgartner, Hans; Kärhä, Petri; Andor, Gyorgy; Ikonen, Erkki; Metrology Research InstituteItem Optical power scale realization using the predictable quantum efficient detector(IOP Publishing Ltd., 2022-01-06) Maham, Kinza; Kärhä, Petri; Manoocheri, Farshid; Ikonen, Erkki; Dept Signal Process and Acoust; Metrology Research InstituteWe report realization of scales for optical power of lasers and spectral responsivity of laser power detectors based on a predictable quantum efficient detector (PQED) over the spectral range of 400 nm – 800 nm. The PQED is characterized and used to measure optical power of a laser that is further used in calibration of the responsivities of a working standard trap detector at four distinct laser lines, with an expanded uncertainty of about 0.05%. We present a comparison of responsivities calibrated against the PQED at Aalto and the cryogenic radiometer at RISE, Sweden. The measurement results support the concept that the PQED can be used as a primary standard of optical power.Item Photoacoustic characteristics of carbon-based infrared absorbers(Elsevier, 2021-09) Rossi, Jussi; Uotila, Juho; Sharma, Sucheta; Laurila, Toni; Teissier, Roland; Baranov, Alexei; Ikonen, Erkki; Vainio, Markku; Tampere University; Patria Aviation; Metrology Research Institute; Dept Signal Process and Acoust; Université de MontpellierWe present an experimental comparison of photoacoustic responsivities of common highly absorbing carbon-based materials. The comparison was carried out with parameters relevant for photoacoustic power detectors and Fourier-transform infrared (FTIR) spectroscopy: we covered a broad wavelength range from the visible red to far infrared (633 nm to 25 μm) and the regime of low acoustic frequencies (< 1 kHz). The investigated materials include a candle soot-based coating, a black paint coating and two different carbon nanotube coatings. Of these, the low-cost soot absorber produced clearly the highest photoacoustic response over the entire measurement range.
