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In this work, we review the viability and precision of the photon-momentum-based optical power measurement method that employs an amplification effect caused by a multi-reflected laser beam trapped in an optical cavity. Measuring the total momentum transfer of the absorbed and re-emitted photons from a highly reflective surface (reflection of the laser beam from an optical mirror) as a force provides the possibility of measuring the optical power with direct traceability to SI units. Trial measurements were performed at two different metrology laboratories: the laboratory for mass/force at the Technical University of Ilmenau, and the clean room laser radiometry laboratory at PTB, with a portable force measurement setup consisting of two electromagnetic force compensation balances. We compared the results of the optical power measurements performed with the force measurement setup, via the photon-momentum-based method, with those performed using a calibrated reference standard detector traceable to PTB's primary standard for optical power, the cryogenic radiometer. The comparison was carried out for an optical power range between 1 W and 10 W at a wavelength of 532 nm, which corresponds to a force of approximately 2000 nN at the upper limit, yielding approximately 2.3% relative standard uncertainty in the case of 33 reflections. Thus, conflating the high-precision force metrology technique at [my]N to nN levels with the optical setup required to achieve specular multi-reflection configuration of the laser beam, where a macroscopic optical cavity with ultra-high reflective mirrors (>99.995%) can adjustably be suspended from the force sensors, depending on required geometry of reflections, we show that the uncertainty of the optical power measurements upon further increase of the nominally applied optical power, the number of laser beam reflections, or the reflectivity coefficient of the mirrors can be markedly reduced.

Micro coordinate measuring machines have been developed for the traceable characterisation of small complex parts, due to the demand in research and industry. These machines require geometrically well characterised probing spheres of ever smaller radii. Currently, there is no established procedure for the measurement of such spheres below radii of 500 [my]m. In this paper we, therefore, propose and investigate an approach which is based on a set of AFM surface scans in conjunction with a stitching algorithm. The strategy was implemented on a nano measuring machine and investigated on a ruby sphere with a radius of 150 [my]m. Although the strategy can generally be applied to the characterisation of a full sphere, we limit ourselves to the measurement of one greate circle (equator). The technique enables the measurement of micro spheres with a high lateral and vertical resolution. The mean radius of the ruby sphere was measured with a standard deviation of 3.7 nm over 6 repetitions. As our experiments have shown, the measurement procedure is at the moment mainly influenced by the shape of the AFM tip which requires further attention.

We present theory, processing steps and first results for a thermally actuated Aluminiumnitride-Platinum membrane with a resonant frequency of the first mode at around 100 kHz and resonant displacements at its center of around 30 µm. The radial-symmetric membrane is broadband opaque for wavelengths from visual light and beyond. An exception is a small pinhole of various diameters below 3 µm in its center. Through thermally induced asymmetric stress inside the multilayer, the clamped membrane bends out. The pinhole in its center will be displaced parallel to the optical axis.The intended use for such a membrane is to replace the traditional confocal pinhole in the detection path of a microscope. Applying a stable known resonant modulation on an acquired signal enables a lock-in principle for a differential confocal depth sensing as shown in [1]. The advantage over the employed tunable acoustic gradient lens (TAG lens) there, is the reduced size, the simplicity of the arrangement and constant illumination properties on the sample.

The PB2 Planck-Balance is a table-top Kibble balance, that is designed for the calibration of class E2 weights in a range of 1 mg up to 100 g. This work presents typical systematic errors which have to be considered during the calibration and will show results for measurements with small masses.