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Register a new userDirect comparisons of European primary and secondary frequency standards via satellite techniques
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We carried out a 26-day comparison of five simultaneously operated optical clocks and six atomic fountain clocks located at INRIM, LNE-SYRTE, NPL and PTB by using two satellite-based frequency comparison techniques: broadband Two-Way Satellite Time and Frequency Transfer (TWSTFT) and Global Positioning System Precise Point Positioning (GPS PPP). With an enhanced statistical analysis procedure taking into account correlations and gaps in the measurement data, combined overall uncertainties in the range of $1.8 times 10^{-16}$ to $3.5 times 10^{-16}$ for the optical clock comparisons were found. The comparison of the fountain clocks yields results with a maximum relative frequency difference of $6.9 times 10^{-16}$, and combined overall uncertainties in the range of $4.8 times 10^{-16}$ to $7.7 times 10^{-16}$.
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The phase noise and frequency stability measurements of 1 GHz, 100 MHz, and 10 MHz signals are presented which have been synthesized from microwave cryogenic sapphire oscillators using ultra-low-vibration pulse-tube cryocooler technology. We present the measured data using independent cryogenic oscillators for the 100 MHz and 10 MHz synthesized signals, whereas previously we only estimated the expected results based on residual phase noise measurements, when only one cryogenic oscillator was available. In addition we present the design of a 1 GHz synthesizer using a Crystek voltage controlled oscillator phase locked to 1 GHz output derived from a cryogenic sapphire oscillator.
We report on the first comparison of distant caesium fountain primary frequency standards (PFSs) via an optical fiber link. The 1415 km long optical link connects two PFSs at LNE-SYRTE (Laboratoire National de m{e}trologie et dEssais - SYst`{e}me de R{e}f{e}rences Temps-Espace) in Paris (France) with two at PTB (Physikalisch-Technische Bundesanstalt) in Braunschweig (Germany). For a long time, these PFSs have been major contributors to accuracy of the International Atomic Time (TAI), with stated accuracies of around $3times 10^{-16}$. They have also been the references for a number of absolute measurements of clock transition frequencies in various optical frequency standards in view of a future redefinition of the second. The phase coherent optical frequency transfer via a stabilized telecom fiber link enables far better resolution than any other means of frequency transfer based on satellite links. The agreement for each pair of distant fountains compared is well within the combined uncertainty of a few 10$^{-16}$ for all the comparisons, which fully supports the stated PFSs uncertainties. The comparison also includes a rubidium fountain frequency standard participating in the steering of TAI and enables a new absolute determination of the $^{87}$Rb ground state hyperfine transition frequency with an uncertainty of $3.1times 10^{-16}$. This paper is dedicated to the memory of Andr{e} Clairon, who passed away on the 24$^{th}$ of December 2015, for his pioneering and long-lasting efforts in atomic fountains. He also pioneered optical links from as early as 1997.
The ePix detector family provides multiple variants of hybrid pixel detectors to support a wide range of applications at free electron laser facilities. We present the results of a systematic study of the influence of radiation induced damage on the performance and lifetime of an ePix100a detector module using a direct attenuated beam of the EuXFEL at 9 keV photon energy and an average power of 10 $mu$W. An area of 20 x 20 pixels was irradiated with an average photon flux of approx. 7 x $10^{9}$ photons/s to a dose of approximately 760$pm$65 kGy at the location of the Si/SiO$_2$ interfaces in the sensor. A dose dependent increase in both offset and noise of the ePix100a detector have been observed originating from an increase of the sensor leakage current. Moreover, we observed an effect directly after irradiation resulting in the saturation of individual pixels by their dark current. Changes in gain are evaluated one and half hours post irradiation and suggest damage to occur also on the ASIC level. Based on the obtained results, thresholds for beam parameters are deduced and the detector lifetime is estimated with respect to the requirements to the data quality in order to satisfy the scientific standards defined by the experiments. We conclude the detector can withstand a beam with an energy up to 1 $mu$J at a photon energy of 9 keV impacting on an area of 1 mm$^2$. The detector can be used without significant degradation of its performance for several years if the incident photon beam intensities do not exceed the detectors dynamic range by at least three orders of magnitude. Our results provide valuable input for the operation of the ePix100a detector at FEL facilities and for the design of future detector technology.
Gravitational waves imprint apparent Doppler shifts on the frequency of photons propagating between an emitter and detector of light. This forms the basis of a method to detect gravitational waves using Doppler velocimetry between pairs of satellites. Such detectors, operating in the milli-hertz gravitational frequency band, could lead to the direct detection of gravitational waves. The crucial component in such a detector is the frequency standard on board the emitting and receiving satellites. We point out that recent developments in atomic frequency standards have led to devices that are approaching the sensitivity required to detect gravitational waves from astrophysically interesting sources. The sensitivity of satellites equipped with optical frequency standards for Doppler velocimetry is examined, and a design for a robust, space-capable optical frequency standard is presented.
The Project 8 experiment aims to measure the neutrino mass using tritium beta decays. Beta-decay electron energies will be measured with a novel technique: as the electrons travel in a uniform magnetic field their cyclotron radiation will be detected. The frequency of each electrons cyclotron radiation is inversely proportional to its total relativistic energy; therefore, by observing the cyclotron radiation we can make a precise measurement of the electron energies. The advantages of this technique include scalability, excellent energy resolution, and low backgrounds. The collaboration is using a prototype experiment to study the feasibility of the technique with a $^{83m}$Kr source. Demonstrating the ability to see the 17.8 keV and 30.2 keV conversion electrons from $^{83m}$Kr will show that it may be possible to measure tritium beta-decay electron energies ($Q approx 18.6$ keV) with their cyclotron radiation. Progress on the prototype, analysis and signal-extraction techniques, and an estimate of the potential future of the experiment will be discussed.
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