Absolute Power Measurements Research Articles

Development of silicon photodetectors for absolute optical power measurement

Traditional methods used to realize the primary standard for the absolute optical power standard rely on expensive equipment and require well-trained personnel for maintenance and measurement activities. Silicon photonics technologies have enabled the development of predictable photodiodes with uncertainty comparable to (or perhaps better than) traditional methods. This work will report these research activities.

Quantitative Electroencephalography in Outpatient Children with Autistic Spectrum Disorders: A Case-Control Study in the Child Welfare Teaching Hospital, Baghdad

Background: The diversity of autism spectrum disorder presentation necessitates the use of simple tests. Quantitative electroencephalography is a low-cost, simple instrument that is being investigated as a clinical tool for monitoring abnormal brain development. Objective: To study brain waves by computer-analyzed EEG (quantitative EEG) in autistic children and correlate the changes to the clinical severity of autistic children. Methods: The study involved 65 children; 30 were recruited from the autism center and the pediatric neurology consultant in the child welfare teaching hospital, Medical City, and met the DSM-5 criteria for autism. Another 35 age-matched, normally-developed ASD children met the DSM-5 criteria, the Childhood Autism Rating Scale, for autism severity. Absolute and relative spectral power measurements were used to investigate brain activity. Results: The absolute and relative delta power increased in the patients as compared to the controls (p<0.05) in all brain regions. There is an association between the disease severity score and absolute and relative delta and theta power in brain areas. The absolute power of the delta wave peaked in the occipital and temporal regions. The relative delta power peaked in the temporal region. Conclusions: The spectrum delta power can aid in the evaluation and classification of ASD. QEEG testing revealed abnormalities in all ASD children and can be a helpful assessment instrument for ASD children.

Interrelations of Clinical, Neurophysiological and Neuroimmunological Parameters in Depressive Patients after COVID-19

The aim of the study was to assess the impact of the coronavirus infection on clinical, neurophysiological and neuroimmunological parameters, as well as on their interrelations in young female depressive patients. Patients: a comparative analysis of quantitative clinical (according to the HDRS-17 scale), neurophysiological (EEG) and neuroimmunological (according to the “Neuro-immuno-test” technology) parameters was carried out in two groups of female depressive patients aged 16–25 years. The first group included 46 patients who recovered from a mild or asymptomatic coronavirus infection (“COVID” group). The second group included 40 patients who were studied and treated before the start of the pandemic (i.e., those who did not have COVID — the “pre-COVID” group) and corresponding to patients of the first group by gender, age, diagnoses, and syndrome structure of disorders. In all patients, prior to the start of the course of therapy, a multichannel EEG was recorded with the measurement of absolute spectral power and neuroimmunological parameters in blood plasma were determined. Methods: clinicalpsychopathological, psychometric, neurophysiological, neuroimmunological, statistical. Results: significantly greater scores of somatic disorders cluster of HDRS-17 scale, and increased amount of slow-wave EEG activity (of delta, theta1 and theta2 subbands) were revealed in the “COVID” group in comparison to patients of “pre-COVID” group. Mean values of neuroimmunological parameters were not differed statistically between two groups, but the values of neuroplasticity markers (levels of autoantibodies to the S100b protein and to the basic myelin protein) in the “pre-COVID” group correlated positively with the spectral power values of the main EEG rhythm (alpha2 and alpha3 sub-bands), and in “COVID” group — with the values of the spectral power of slow-wave EEG activity, reflecting a reduced brain functional state. Conclusion: the results obtained indicate that coronavirus infection, even in mild or asymptomatic forms, affects the clinical, neurophysiological and neuroimmunological parameters, as well as their interrelations in young female depressive patients.

Absolute photon power measurements at the European XFEL instruments

The average photon flux is one of the main parameters of any photon source. At the European XFEL (EuXFEL), this is continuously monitored in the tunnels by X-ray Gas Monitors (XGMs) [1-3]. However, to measure the absolute value of the X-ray flux at the sample location in the scientific end-stations, in general a smaller device is required since the XGMs and their associated differential pumping stages are very space demanding. Therefore, a miniature solid-state room-temperature calorimeter based on a design by AIST, Japan [4-8] was commissioned with beam at the Spectroscopy and Coherent Scattering (SCS) instrument where it could be located directly downstream of an XGM. This allowed for validation of the gas-based measurements with a solid-state physics method with an independent absolute calibration. The calorimeter was then applied at the High Energy Density (HED) instrument to characterize the beamline transmission and to calibrate a commercial laser power meter (LPM) [9] as a secondary relative monitor for X-ray measurements. This contribution describes the technical parameters and capabilities of the calorimeter and LPM and presents the measurements taken at SCS and HED.

Relationship between Lower Limbs Performance and Spinal Alignment in Parkinson's Disease Patients: An Observational Study with Cross Sectional Design.

Parkinson’s disease (PD) is a progressive neurodegenerative disease determining spinal deformities and muscle rigidity, weakness and dystonia that can be related to a change in muscular output during sit-to-stand tasks (STS). Purpose: The aim of this study was to determine the impacts of spinal alignment on lower limbs performance during STS tasks in Parkinson’s disease (PD) patients and healthy controls. Methods: In total, 43 consecutive PD patients (“PD” Group, 25 males and 18 females; age 73.7 ± 7.1) and 42 people not affected by any type of neurological disease (“CON” Group, 22 males, 20 females; age 69.8 ± 6.0) participated in the observational study. The clinical assessment included: IPAQ (International Physical Activity Questionnaire), Hoehn Yahr score, plumb-line distance from the spinous process of C7, kyphosis apex and the spinous process of L3 and S1. We used the Muscle Quality Index test (MQI) to assess muscle power output during STS in both groups. Results: The MQI test measurements of absolute and relative lower limb power was significantly lower in the PD group, in addition to a negative correlation with age and a positive correlation with PL-L3 in that group of patients. Conclusions: A final consideration regarding our results leads to the possibility that the preservation of lumbar lordosis may be one of the factors for maintaining efficient biomechanics of the lower limb muscles, with the preservation of the physiological contractile characteristics of these muscles being the objective for a multidisciplinary rehabilitation based on postural exercises of the spine and a program of training exercises for the lower limb muscles.

Generalized electrical substitution methods and detectors for absolute optical power measurements

We have developed generalized methods for electrical substitution optical measurements, as well as cryogenic detectors which can be used to implement them. The new methods detailed here enable measurement of arbitrary periodic waveforms by an electrical substitution radiometer (ESR), which means that spectral and dynamic optical power can be absolutely calibrated directly by a primary standard detector. Cryogenic ESRs are not often used directly by researchers for optical calibrations due to their slow response times and cumbersome operation. We describe two types of ESRs with fast response times, including newly developed cryogenic bolometers with carbon nanotube absorbers, which are manufacturable by standard microfabrication techniques. These detectors have response times near 10 ms, spectral coverage from the ultraviolet to far-infrared, and are ideal for use with generalized electrical substitution. In our first tests of the generalized electrical substitution method with FTS, we have achieved uncertainty in detector response of 0.13% (k = 1) and total measurement uncertainty of 1.1% (k = 1) in the mid-infrared for spectral detector responsivity calibrations. The generalized method and fast detectors greatly expand the range of optical power calibrations which can be made using a wideband primary standard detector, which can shorten calibration chains and improve uncertainties.

Extending the Frequency Range of the Power Sensor Calibration Factor Determination

Power sensors (PSs) are used in many RF power measurements, so a determination of their accuracy in the full frequency range of interest is very important. The calibration factor (CF) of a PS, or more precisely, the uncertainty of its measurement, represents the parameter that has a significant impact on the absolute power measurement uncertainty. An improved method for the CF determination of PS using a thermal converter (TC) as a reference standard and a resistive power splitter for frequencies below 10 MHz is proposed. The improvement of the proposed method is based on the experimental determination of the power splitter symmetry as the most influential parameter, which reduces the overall measurement uncertainty more than six times. The symmetry characterization of the power splitter is performed by an alternative method with the TC. As a result, traceability of the RF power below 10 MHz and extended frequency range of CF measurement to dc with competitive measurement uncertainty, using the existing equipment is established. The majority of the broadband RF power standards and network analyzers operate at high frequencies. The proposed method overcomes the lack of their availability at frequencies below 10 MHz and can be applied to all types of average PSs. Uncertainty sources analysis and measurement uncertainty budget for the normalized CF of a diode PS is presented as an example.

Development of electrical substitution Fourier transform spectrometry for absolute optical power measurements.

We have demonstrated the first continuous-scan electrical substitution Fourier transform spectrometer (ES-FTS), which serves initially as an apparatus for absolute spectral responsivity calibrations of detectors over the wavelength range from 1.5 µm to 11 µm. We present data on the realization of a spectral detector-comparator system with high accuracy, high dynamic range, high spectral resolution and fast measurement in the infrared region, which is tied directly to an absolute power scale through electrical substitution. The ES-FTS apparatus employs a commercial Fourier transform spectrometer and a custom electrical substitution bolometer detector to enable spectrally-resolved absolute optical power measurements. A generalization of electrical substitution techniques enables determination of the voltage waveform that must be applied to the bolometer's electrical heater to cancel the optical signal from a Michelson interferometer in order to quantify the time-dependent optical power incident on the bolometer. The noise floor of the electrical substitution bolometer is on the order of 10 pW/Hz½ and its response is expected to be linear from the noise floor to 1 mW. A direct comparison between a pyroelectric standard detector and the ES-FTS has been performed, and experimental results reported here show great potential for this technique.

High amplification laser-pressure optic enables ultra-low uncertainty measurements of optical laser power at kilowatt levels

We present the first measurements of kilowatt laser power with an uncertainty less than 1%. These represent progress toward the most accurate measurements of laser power above 1 kW at 1070 nm wavelength and establish a more precise link between force metrology and laser power metrology. Radiation pressure, or photon momentum, is a relatively new method of non-destructively measuring laser power. We demonstrate how a multiple reflection optical system amplifies the pressure of a kilowatt class laser incoherently to improve the signal to noise ratio in a radiation pressure-based measurement. With 14 incoherent reflections of the laser, we measure a total uncertainty of 0.26% for an input power of 10 kW and 0.46% for an input power of 1 kW at the 95% confidence level. These measurements of absolute power are traceable to the SI kilogram and mark a state-of-the-art improvement in measurement precision by a factor of four.

Running power: lab based vs. portable devices measurements and its relationship with aerobic power

ABSTRACT In recent years, different companies have developed devices that estimate “running power”. The main objective of this paper is to evaluate the effect of running speed on aerobic and running powers measured using force plates and by different devices. The second objective is to evaluate the relationship between aerobic power and running powers measured using force plates and by different devices. We enrolled 11 subjects in the study, they performed 5-min running trials at 2.22, 2.78, 3.33, 3.89 and 4.44 m/s respectively on a force-measuring treadmill while we collected metabolic data. We calculated running power as the dot product of ground reaction force and velocity of the centre of mass and compared it to the running power estimates of three devices: Skillrun (Technogym), Stryd Summit Powermeter (Stryd) and Garmin HRM-Run (Garmin). We found statistically significant linear correlations with running powers measured by all devices and running speed. Although absolute running power measurements were different among devices, an increase of 1 m/s in running speed translated to an increase of 0.944 W/kg in running power (p < 0.001). We found statistically significant linear correlations with running powers measured by all devices and aerobic power, in particular: as aerobic power increases by 1 W/kg, running power increases by 0.218 W/kg for all devices (p < 0.001). For level treadmill running, across speeds, running power measured by commercially available devices reflects force-based measurements and it can be a valuable metric, providing quasi real-time feedback during training sessions and competitions. Highlights We evaluated the effect of running speed on aerobic and running powers measured using force plates and by different devices. We also compared the relationship between aerobic power and running powers measured using force plates and by different devices. We found statistically significant linear correlations with running powers measured by all devices and aerobic power, in particular: as aerobic power increases by 1 W/kg, running power increases by 0.218 W/kg for all devices. For level treadmill running, across speeds, running power measured by commercially available devices reflects force-based measurements and it can be a valuable metric, providing quasi real-time feedback during training sessions and competitions.

Measurement of HFETR reactor power by improved 16N gamma spectrum analysis method

To increase redundancy and diversity of the reactor power measurement, a system for the measurement of reactor power can be established based on neutron activation analysis using 16O(n,p)16N reaction. In this work, gamma spectrums from the coolant of HFETR core are continuously detected by 16N monitor with NaI(Tl) detector and the count rates in the spectrum range of 4.5 MeV-7.5 MeV are obtained. Meanwhile, the overlapping peaks in the given spectrum range are decomposed with Levenberg-Marquardt method during the operation of HFETR. The results confirm that the count rates of full-energy peak, single-escape peak and double-escape peak of 6.13 MeV gamma spectrums is proportionate to the increased reactor power measured by other monitors such as compensated ionization chamber and thermal power. It is possible to achieve the absolute nuclear power measurement by adopting the count rate of 16N 6.13 MeV peak, detection efficiency of detector and 16N source term.

Linking the Power Scales of Free-Space and Waveguide-Based Electromagnetic Waves

Two independent methods of absolute power measurement of electromagnetic waves are compared in the millimeter-wave range. At the National Metrology Institutes (NMIs), dependent on frequency and wave propagation, electromagnetic power is differently traced back to the International System of Units (SI), i.e., from microwave up to millimeter-wave frequencies in coaxial lines and metallic waveguides and terahertz frequencies in free space. As state-of-the-art waveguide-based power sensors and free-space power detectors are overlapping with respect to their operating frequency, for the first time, a comparison of both independent power scales has been carried out in the millimeter-wave range. The experiment verified the consistency of both traceability approaches within their uncertainties.

Miniature force sensor for absolute laser power measurements via radiation pressure at hundreds of watts.

We present a small power meter that detects the radiation pressure of an incident high-power laser. Given its small package and non-destructive interaction with the laser, this power meter is well suited to realizing a robust real-time, high-accuracy power measurement in laser-based manufacturing environments. The incident laser power is determined through interferometric measurement of displacement of a 20 mm diameter high reflectivity mirror, mounted at the center of a dual element spiral flexure. This device can measure laser power from 25 W to 400 W with a 260 m W/H z noise floor and ≤ 3.2% expanded uncertainty. We validate our device against a calibrated thermopile with simultaneous measurements of an unpolarized 1070 nm laser and report good agreement between the two systems. Finally, by referencing to an identical mechanical spring that does not see the incident laser, we suppress vibration noise in the power measurement by 14.8 dB over a 600 Hz measured bandwidth. This is an improvement over other radiation pressure based power meters that have previously been demonstrated.

The effects of surface roughness on specular diagnostics in shocked experiments.

Many shock experiments, whether impact, laser, or magnetically driven, use reflected optical light from shocked samples to diagnose their material properties. Specifically, optical velocimetry diagnostics, which do not require absolute power measurements, are regularly used to obtain equation-of-state information of materials. However, new diagnostics will be necessary to expand the realm of measured material properties, and many useful diagnostic techniques do require absolute measurements. Thus, it is important to understand what happens at the reflective surface of shock experiments, and the effect scattering has on the light collection of optical probes. To this end, we present results from experiments done to observe the behavior of a reflected beam from a specular coating on an optical window during shock impact. We find that the specular condition of the coating is adversely affected by the shock front, but this can be mitigated by minimizing roughness on the surface preceding the coating.

Crystallization kinetics study of melt-spun Zr66.7Ni33.3 amorphous alloy by electrical resistivity measurements

In this paper, the electronic transport properties of as-spun Zr66.7Ni33.3 alloys were studied in detail by a combination of electrical resistivity and absolute thermoelectric power measurements over a temperature range from 25 up to 400 °C. Moreover, the isochronal and isothermal crystallization kinetics of Zr66.7Ni33.3 glassy alloy has been investigated based on the electrical resistivity measurements. The comparative study of the crystallization kinetics of these binary amorphous alloys was carried out, for the first time to our knowledge, using an accurate method for electrical resistivity measurements. In the isochronal heating process, the apparent activation energy for crystallization was determined to be, respectively, 371.4 kJ mol−1 and 382.2 kJ mol−1, by means of Kissinger and Ozawa methods. The Johnson–Mehl–Avrami model was used to describe the isothermal transformation kinetics, and the local Avrami exponent has been determined in the range from 2.97 to 3.23 with an average value of 3.1, implying a mainly diffusion-controlled three-dimensional growth with an increasing nucleation rate. Based on an Arrhenius relationship, the local activation energy was analyzed, which yields an average value Ex = 376.2 kJ mol−1.

Temperature dependence of the electrical resistivity and absolute thermoelectric power of amorphous metallic glass Ni33.3Zr66.7

Electron transport properties and thermal stability of Ni33.3Zr66.7 metallic glass (MG) have been studied using an original device for simultaneous measurements of electrical resistivity and absolute thermoelectric power (ATP) controlled by a LabView software written by one of us. The electrical resistivity and absolute thermoelectric power were measured simultaneously and very accurately over a temperature range from 25 to 400°C with a nominal heating rate of 0.5K min−1. The electronic thermal conductivity was also determined using the Wiedemann–Franz law in the same temperature range. Due to its high efficiency, this technique is more and more used because it is characterized by a high sensitivity to detection of the phase transitions related to electronic transport, which is the aim of this study. Analysis of the temperature dependence of the resistivity and ATP of the Ni33.3Zr66.7 glassy ribbons proves the potential of this characterization method to study the thermal behavior of metallic glasses. The crystal structure and the morphology of Ni33.3Zr66.7 metallic glass in the as-quenched state and after heat treatments were studied using X-ray diffraction (XRD), and scanning electron microscope (SEM).

Experimental investigation of nitric oxide radiation in the shock-heated air

The experimental results of the absolute measurements of spectral radiation of air were obtained on the double diaphragm shock tube of Laboratory of Kinetic Process in Gases of Institute of Mechanics MSU. The radiative properties of nitric oxide in the spectral range 190-290 nm were investigated experimentally. The time dependence of the emission of molecular bands for NO shock wave velocities of 4-10 km / s were obtained. The article discusses the problems of absolute power measurement in the radiation behind shock wave front

Planar hyperblack absolute radiometer.

The absolute responsivity of a planar cryogenic radiometer fabricated from micromachined silicon and having carbon nanotubes, as the absorber and thermistor were measured in the visible and far infrared (free-field terahertz) wavelength range by means of detector-based radiometry. The temperature coefficient of the thermistor near 4.8 K and noise equivalent power were evaluated along with independent characterization of the window transmittance and specular reflectance of the nanotube absorber. Measurements of absolute power by means of electrical substitution are compared to the German national standard and the uncertainty of the radiometer responsivity as a function of wavelength is summarized.

Determination of x-ray free electron laser power using a room-temperature calorimeter

A room-temperature calorimeter was developed for the absolute laser power measurement of x-ray free electron lasers (XFELs) at the SPring-8 Angstrom Compact free electron LAser facility in Japan. In the photon energy range from 4.5 keV to 15 keV, this calorimeter was demonstrated to accurately measure laser powers of XFEL up to 6.9 mW. In addition, an online beam monitor, based on the detection of backscattered x-rays from a thin diamond film, was calibrated with the room-temperature calorimeter. The calibration results were compared with those obtained previously with a cryogenic radiometer (the primary standard detector for synchrotron radiations in Japan). The calibration results obtained with the two detectors agreed well within 1.2%, which is well below their combined relative standard uncertainty. Moreover, the spectral responsivity of the beam monitor was found to show a strong photon energy dependence owing to Debye–Scherrer diffraction patterns from the thin-film.

Robert Street 1920–2013

Following wartime work on radar and a University of London PhD awarded for measurement of absolute power, Bob Street developed his interest in low-temperature magnetism in solids while on the staff at Sheffield University. In 1960 he became Foundation Professor of Physics at Monash University where he built a department with strong capabilities in solid state physics. His own research continued at Monash but was put aside when he became Director of the Research School of Physical Sciences at the Australian National University (1973–7) and then Vice-Chancellor at the University of Western Australia (1978–86). Although the ANU experience was not a happy one, he flourished at UWA where his initiatives and strategic thinking laid the groundwork for advancement of the university. Street had kept up with advances in his research field and upon retirement he went back to it with notable success in publication, supervision of research students, acquisition of research grants and fruitful collaborations. He is fondly remembered as a first class physicist with a passion for cricket.