The use of the radiation pressure of a laser field, as an effect of the momentum transfer of the absorbed and re-emitted photons, suggests rather a complementary than an alternative possibility for metrology to generate calibration forces or to calibrate the optical power directly traceable to the International System of Units (SI). This paper reports a method and experimentally measured evidence on options to extend the effective use of radiation pressure for generating optical forces in the sub-microNewton (μN) range. Among other features and results presented, we emphasize the variability in controlling the accuracy of these forces through the proper utilization of the power of a multi-pass laser beam (semi- or completely) locked within confined systems. The direct measurements of these forces, augmented due to the partial or total momentum transfer of the photons of a multi-pass laser beam extended from several hundreds of picoNewton (pN) up to sub-μN range for the same power of laser source, are done by a precision force measurement system and compared with basic theoretical computations. We also discuss the opportunities to probe the fundamental physical limits associated with this method and to the considerable extent other competing contributing effects that might be regarded as sources of errors in metrological tasks.

A balance is proposed, which allows the calibration of weights in a continuous range from 1 mg to 1 kg using a fixed value of the Planck constant, h. This so-called Planck-Balance (PB) uses the physical approach of Kibble balances that allow the Planck constant to be derived from the mass. Using the PB no calibrated mass standards are required during weighing processes any longer, because all measurements are traceable via the electrical quantities to the Planck constant, and to the meter and the second. This allows a new approach of balance types after the expected redefinition of the SI-units by the end of 2018. In contrast to many scientific oriented developments, the PB is focused on robust and daily use. Therefore, two balances will be developed, PB2 and PB1, which will allow relative measurement uncertainties comparable to the accuracies of class E2 and E1 weights, respectively, as specified in OIML R 111-1. The balances will be developed in a cooperation of the Physikalisch-Technische Bundesanstalt (PTB) and the Technische Universität Ilmenau in a project funded by the German Federal Ministry of Education and Research.

Practical means of generation and calibration of the small precision forces in static and dynamic regimes around 1 Hz by the usage of radiation pressure effect from 1 W continuous wave visible (diode) laser light is presented. The additive effect of the transfer of photon momentum, caused by non-overlapping multiply reflecting laser beam locked within a quasi-passive and/or active macroscopic cavity system, is employed. The effective laser power (partially trapped experimentally) is amplified, such that the optically generated forces are increased from hundreds of pN to sub- N level. The results presented in this paper should be seen as a means for extending the edge of practically verifiable lower limits of SI-traceable force metrology.

In this paper we present the progress in development of a table-top version of the Kibble balance under the name Planck-Balance 2 (PB2). The PB2 is developed as a collaboration effort between the Technische Universität Ilmenau (TU Ilmenau) and Physikalisch-Technische Bundesanstalt (PTB) aiming for automatized mass calibration of the set of weights in the range from 1 mg to 100 g within the required uncertainties as stated by OIML recommendation R111 for weights of E2 class. We describe the design and the operational performance of the PB2 system in detail, the results of rigorous investigations of the error sources and subsequent improvements made since the beginning of the project in early 2017, the measurement data with the corresponding relative uncertainties and the preliminarily obtained uncertainty budget.

In this paper we present a force measurement system that is developed based on the principle of torsion balance. The system will primarily be used as a flowmeter for weakly electrically conducting fluids using the method of Lorentz force velocimetry. The paper aims to improve the technique of precision force measurements in the horizontal direction with a high dead load. The tilt dependency of the system is tested, and the tilt sensitivity is minimized to within 5.9 • 10 −2 N rad −1 , which is the required limit of the application. The voltage of the photoelectrical position sensor as an original output signal of the system is proportional to the introduced force. This relationship is calibrated using two different force sensing methods: (a) by generating known force values using variability aspects of the tilt dependency of the system, or (b) by applying electromagnetic forces generated with a miniature voice coil actuator. Additionally, the static and dynamic characteristics of the system are identified, from which the effective stiffness of the system is determined as 0.59 N m −1 , and the undamped natural frequency is 0.06 Hz with the settling time of 124 s. Finally, the force measurement system is tested extensively at the open-loop operational mode, enabling us to detect forces with 18.2 nN resolution in its linear working range of approximately ± 30 µN.