A GPS-referenced wavelength standard for high-precision displacement interferometry at λ = 633 nm

Since the turn of the millennium, the development and commercial availability of optical frequency combs has led to a steadily increase of worldwide installed frequency combs and a growing interest in using them for industrial-related metrology applications. Especially, GPS-referenced frequency combs often serve as a "self-calibrating" length standard for laser wavelength calibration in many national metrology institutes with uncertainties better than u = 1 × 10^-11. In this contribution, the application of a He-Ne laser source permanently disciplined to a GPS-referenced frequency comb for the interferometric measurements in a nanopositioning machine with a measuring volume of 200 mm × 200 mm × 25 mm (NPMM-200) is discussed. For this purpose, the frequency stability of the GPS-referenced comb is characterized by heterodyning with a diode laser referenced to an ultrastable cavity. Based on this comparison, an uncertainty of u = 9.2 × 10^-12 (τ = 8 s, k = 2) for the GPS-referenced comb has been obtained. By stabilizing a tunable He-Ne source to a single comb line, the long-term frequency stability of the comb is transferred onto our gas lasers increasing their long-term stability by three orders of magnitude. Second, short-term fluctuations-related length measurement errors were reduced to a value that falls below the nominal resolving capabilities of our interferometers (ΔL/L = 2.9 × 10^-11). Both measures make the influence of frequency distortions on the interferometric length measurement within the NPMM-200 negligible. Furthermore, this approach establishes a permanent link of interferometric length measurements to an atomic clock

Spinach hexokinase I is located in the outer envelope membrane of plastids

AbstractThe subcellular localization of hexokinase activities in plant cells has been a matter of debate for a long time. We have isolated a hexokinase cDNA fragment from glucose-fed spinach leaves using a differential display reverse transcription-PCR approach. The corresponding cDNA was expressed in Escherichia coli and an antiserum, raised against the recombinant protein, was used in subcellular localization studies. The spinach hexokinase could be localized primarily to the outer envelope membrane of chloroplasts where it is inserted via its N-terminal membrane anchor. We suggest that the chloroplast envelope hexokinase is involved in the energization of glucose export from plastids rather than in the sugar-sensing pathway of the plant cell

A straightness measuring interferometer characterised with different wedge prisms

Independently of the component used to introduce a divergence angle between the two probing beams of straightness interferometers, their uncertainty is limited by three main errors linked to each other: their resolution, the influence of refractive index gradients and the topography of the straightness reflector. The larger the divergence angle the higher is the resolving capability, but also the potential influence of the other two error sources. A fully fibre-coupled heterodyne interferometer was successively equipped with three different wedge prisms to investigate the optimal divergence angle under laboratory conditions. For that, the straightness interferometer was qualified with the Nanometer Comparator, which is a one-dimensional line scale interferometer with an additional straightness measurement capability. This feature is based on the traceable multi-sensor method, where an angle measurement embodies the “straightedge”. Therefore, the qualification of the straightness interferometer was also a comparison of two different straightness measurement methods. The influence of the refractive index gradients of air did not increase with interspaces between the probing beams larger than 11.3 mm. Therefore, over a movement range of 220 mm, the lowest uncertainty was realized with the largest divergence angle. The dominant uncertainty contribution arose from the uncorrected mirror topography determined with sub-nanometre uncertainty with the Nanometer Comparator

Fast and accurate: high-speed metrological large range AFM for surface and nanometrology

Low measurement speed remains as a major shortcoming of the scanning probe microscopic techniques. It leads not only to a low measurement throughput, but also to a significant measurement drift over the long measurement time needed (up to hours or even days). In this paper, development of a high speed metrological large range atomic force microscope (HS Met. LR-AFM) with a capable measurement speed up to 1 mm/s is presented. In its design, a high accurate nanopositioning and nanomeasuring machine (NMM) is combined with a high dynamic flexure hinge piezo stage to move sample. The AFM output signal is combined with the position readouts of the piezo stage and the NMM to derive the surface topography. This design has a remarkable advantage that it well combines different bandwidth and amplitude of different stages/sensors, which is required for high speed measurements. While the HS Met. LR-AFM significantly reduces the measurement time while maintains (or even improves) the metrological performance than the previous Met. LR-AFM, its application capabilities are extended significantly. Two application examples, the realisation of reference areal surface metrology and the calibration of a kind 3D nano standards, have been demonstrated in the paper in detail