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Josephson junction devices; laser femtosecond combs; impedance measurement; watt balance; DC voltage measurement; RF free field measurement; AC power measurement; capacitance measurement; time and frequency measurement; inductance measurement; Avogadro constant determination; optical frequency standards using trapped ions/atoms; RF guided wave measurement; cryogenic current comparators; and measurement...
Abstract form only given. Magnetic resonance imaging (MRI) emerged from nuclear magnetic resonance (NMR) in the early 1970s. It was clear from the first images that a conceptual breakthrough was required to speed up the imaging process from around one hour for those early images to something more acceptable in medical diagnosis. This step forward came in 1975-6 with the realisation that single-shot...
Abstract form only given. During the past five years, femtosecond laser frequency comb synthesizers have firmly established their role as ultraprecise tools for optical frequency metrology. The development of these comb synthesizers will be reviewed, and their present and future role in physics and metrology will be discussed
A synthesizer of precision AC waveforms based on a binary SINIS Josephson junction array has been developed. The array segments are individually biased using a high-speed bias source with a 250 ns switching time between voltage steps. The accuracy limitations of the system will be discussed and various measurements between the synthesizer and thermal converters presented
We are developing MoSi2-barrier stacked-junction arrays for Josephson voltage standards in order to increase the output voltage, operating bandwidth, and operating margins. In this paper we present measurements of a programmable voltage standard circuit with double-stacked arrays, where two junctions are fabricated in each stack. Although a mask defect prevented operation of one-eighth of the fabricated...
A programmable Josephson voltage standard chip using arrays of NbN/TiN/NbN/TiN/NbN double-junction stacks was fabricated and operated at 10 K. The circuit with over 260,000 junctions showed constant voltage steps at +/- 6 V when driven at 11 GHz microwave bias. Further investigation is required to achieve 10 V operation at the desired design frequency of 19 GHz
Recent advances in circuit design and fabrication of superconducting integrated circuits have enabled us to demonstrate for the first time an ac Josephson voltage standard (ACJVS) that generates both ac and dc waveforms up to 242 mV peak voltage. Using a FFT (fast Fourier transform) spectrum analyzer and an ac/dc transfer standard, we characterize ACJVS operating margins by performing "flat-spot"...
The European JAWS project addresses the lack of instrumentation and knowledge for accurate and traceable measurement and generation of alternating (AC) voltage with arbitrary waveforms. The objective is to develop a standard based on a Josephson Arbitrary Waveform Synthesizer (JAWS), a precise instrument that links the generated voltage to the Josephson effect, which in turn relates the voltage to...
Two types of comparisons using transportable femtosecond laser combs have been performed in France and the USA, respectively. The agreement among the combs, when referenced to a hydrogen maser, is on the sub-hertz level at 563 THz. When the combs are referenced to an optical standard, the agreement among four combs was much improved and found to be < 1 mHz at 456 THz
Absolute frequencies of an acetylene-stabilized laser at 1542 nm and an iodine-stabilized Nd:YAG at 1319 nm are measured at their second harmonics by use of a femtosecond optical comb based on a mode-locked Ti:sapphire laser. A frequency measurement system based on a mode-locked fiber laser (1.56mum) is also being developed for metrological applications in the telecommunication bands
A second femtosecond optical frequency comb has been implemented at NPL. This higher repetition rate system offers several advantages over our existing comb, and enables the accuracy of the frequency measurement process to be tested. Results of absolute frequency measurements carried out using the two different systems are compared
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