Abstract We report the first replication of a high-precision measurement of the gravitational constant, G . The experiment employed the torsion balance originally designed and constructed at the International Bureau of Weights and Measures (BIPM) approximately three decades ago. Using the same apparatus and geometry, with several modifications documented in this work, we determined G = ( 6.67387 ± 0.00038 ) × 10 − 11 m 3 kg − 1 s − 2 , corresponding to a relative standard uncertainty of 5.7 × 10 − 5 . The result is lower by 2.5 × 10 − 4 relative to the BIPM determination. This replication provides an independent verification of one of the most precise torsion-balance determinations of G and contributes to assessing the reproducibility limits of current experimental techniques in measurements of the gravitational constant.

Abstract We report high-precision measurements of the static electric dipole polarizabilities for methane (CH4), carbon monoxide (CO), and oxygen (O2) using an optical refractometer operating at 1566 nm. The dynamic polarizabilities at 1566 nm were converted to static polarizabilities via dipole oscillator strength distributions. The achieved relative standard uncertainties are 45 ppm for CH4, 49 ppm for CO, and 46 ppm for O2. Our results are in excellent agreement with previous refractive index and dielectric constant measurements, while improving the precision by over two orders of magnitude for CH4 and CO. These data provide a reliable benchmark for molecular polarizability calculations and contribute to accurate modeling of intermolecular dispersion forces and gas metrology.

Abstract Tabletop version Kibble balances are a significant developing trend for mass realizations following the revised International System of Units. A key innovation through the miniaturization of the Kibble balance from a large-scale instrument into a tabletop device is making the quantum-based realization of mass accessible to a wider range of calibration laboratories and industries. This paper presents a tabletop Kibble balance design at Tsinghua University targeting E2-accuracy class mass calibrations from 1 g to 1 kg. For calibrating a mass of 1 kg, for instance, the required relative standard measurement uncertainty must be below 0.27 ppm to meet E2-accuracy class. Major components and features of the proposed system are discussed. A novel method of multi-harmonic excitation is proposed to improve the coil-motion linearity during velocity measurement. We show that injecting odd-order harmonics into the motion-driving current can significantly improve the uniformity of the coil’s moving velocity, while the second-order component can address the asymmetry between upward and downward movements. This achieves a flat velocity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>v</mml:mi> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi>v</mml:mi> <mml:mo>&lt;</mml:mo> <mml:mn>5</mml:mn> <mml:mi mathvariant="normal">%</mml:mi> </mml:mrow> </mml:math> over 60% of the motion cycle.

Abstract Reliable measurement of the total radiant flux of ultraviolet light-emitting diodes (UV LEDs) is essential for performance evaluation but remains challenging. We report an SI-traceable gonio-spectroradiometer developed at KRISS to measure UV LEDs across 250 nm–500 nm. The system integrates a double-grating spectroradiometer with a goniometer, effectively suppressing spectral stray light and fluorescence that affect integrating-sphere methods. Total radiant flux values of 119 mW, 164 mW, and 176 mW were obtained for LEDs with nominal peaks at 279, 368, and 410 nm, with expanded uncertainties of 1.6%–2.6% ( k = 2). Results agreed with integrating-sphere measurements within uncertainties, while demonstrating superior accuracy for UV sources. This work establishes a traceable and robust method for UV LED flux measurement, supporting standardization in research and industry.

Abstract In the framework of metrology for the new emerging wireless standards such 5G New Radio (NR), the traceable calibration of 5G NR measuring receivers is presented in this contribution. A reference setup to measure the power of cell-specific synchronization resource elements in downlink 5G New Radio (NR) signals is introduced, providing the traceability of the measurements to the International System of Units (SI). This setup can be used to calibrate 5G code-selective measuring receivers that are utilized for the measurements of the radiation from base stations for mobile communication. This setup can also be used to calibrate not only the 5G signal receivers, but also the 5G generators. The method relies on the traceable measurements of the downlink signal generator by using an oscilloscope. It employs offline digital signal processing (DSP) demodulation algorithms that account for digital down-conversion, timing synchronization, frequency synchronization, phase synchronization, and robust 5G cell identification to generate the downlink time-frequency 5G grid. The applicability of this methods for both sub 6 GHz and millimeter wave frequency ranges is proven with experiments. Experimental results from conducted test scenarios demonstrate calibration capabilities with typical uncertainties of 0.05 dB (k=2). Moreover, the application of this method for the calibration of two commercial product and also the RF exposure assessment considerations are also explained in detail.

Abstract After the redefinition of the kelvin in 2019, several start-of-the-art primary gas thermometry techniques were successfully implemented at low-temperature regions. To further make a direct and reliable international comparison of thermodynamic temperature T , we have developed an ultra-stable cryogenic international temperature comparator (CITC) working from 4 K to 25 K. Based on our design and developed temperature control methods, ultra-high stable temperature was achieved with stabilities (standard deviation) better than 10 μK from 4 K to 25 K. The long-term temperature instability is 6.1 μK@4 K, 6.7 μK@5 K, 7.8 μK@13.8 K and 7.4 μK@24.6 K with a sampling time of 33.6 s. Moreover, multibridge, especially four-bridges, comparison and calibration methods were proposed to realize temperature measurements in a more precise and efficient way. The feasibility was demonstrated by using one AC bridge and three super-thermometers. The performance of CITC and the proposed methods in this work showed their great superiority to be used for temperature comparison and calibration.

International audience

Abstract The current definition of the System of unit second based on the Cs ground state hyperfine transition is expected to be replaced by a new definition based on optical frequency standards in the next decade. Several options are currently under consideration for the new definition, including a definition based on the weighted geometric mean of several transitions. In this paper, we review several properties of this option, and most notably introduce a quantitative method to set the weights of transitions, and a graphical representation of the unit that make the distinction between the definition and the realisation of the unit easier to understand.

Abstract The effect of wavefront aberrations, arising from both Raman beam phase distribution and atomic cloud thermal expansion, represents a critical error in atom gravimeters. This work introduces a strategy to reduce and evaluate the effect of wavefront aberrations in an atom gravimeter. First, the optical elements were installed inside the vacuum chamber to minimize the uncertainty of wavefront aberrations effect; Second, a method based on combining precise optical surface measurements with atomic cloud parameters characterization was employed to evaluate this effect; finally, two distinct modulation experiments were conducted to verify the correctness of the evaluation results. Based on this strategy, the uncertainty of wavefront aberrations effect was determined to be 1.4 µGal (1 µGal = 1 × 10−8 m s−2), and the total uncertainty of the atom gravimeter was thus reduced to 1.6 µGal. This study proposes a comprehensive methodology for evaluating the effect of wavefront aberrations in atom gravimeters, which will significantly advance the development of atom interferometers toward higher precision measurements.

Abstract In the solar reflective band, the on-board calibration method based on a solar diffuser (SD) is the mainstream calibration method. However, the calibration accuracy is limited by the measurement accuracy of the SD bidirectional reflectance distribution function (BRDF) in the laboratory. The limitations of the light sources and detectors hinder accurate BRDF measurements in the short-wave infrared band, particularly beyond 1700 nm. In this study, the angle integration-band crossing transfer (AIBCT) method is proposed for SD BRDF measurement to avoid the influence of the Fourier spectrometer's signal processing and detector nonlinearity in the absolute measurement. The method utilized the relationship between the BRDF and directional-hemispherical reflectance, and calculated the spectral distribution of the SD BRDF at the standard in-plane geometry with an 0° incidence zenith angle and a 45° reflection zenith angle (0:45) by integration. The absolute measurement result of the 0:45 SD BRDF at 1150 nm was used as the standard for transfer to the short-wave infrared band. The SD BRDF at 0:45 was generalized to other geometries through relative measurements based on the reciprocity theorem. The mean relative error of the results of the AIBCT and absolute measurement methods was less than 0.3 % in the range of 1100 nm to 1600 nm. Analysis of the results showed that the AIBCT method’s measurement uncertainty (coverage factor k = 2) of the 0:45 SD BRDF is better than 0.84 % at 1100 nm to 2300 nm and 1.05 % at 2300 nm to 2500 nm. Furthermore, the AIBCT method was found suitable for the ultraviolet band.