The frequency stability of an atomic fountain clock was significantly improved by employing an ultra-stable local oscillator and increasing the number of atoms detected after the Ramsey interrogation, resulting in a measured Allan deviation of 8.3 × 10(-14)τ(-1/2)). A cryogenic sapphire oscillator using an ultra-low-vibration pulse-tube cryocooler and cryostat, without the need for refilling with liquid helium, was applied as a local oscillator and a frequency reference. High atom number was achieved by the high power of the cooling laser beams and optical pumping to the Zeeman sublevel m(F) = 0 employed for a frequency measurement, although vapor-loaded optical molasses with the simple (001) configuration was used for the atomic fountain clock. The resulting stability is not limited by the Dick effect as it is when a BVA quartz oscillator is used as the local oscillator. The stability reached the quantum projection noise limit to within 11%. Using a combination of a cryocooled sapphire oscillator and techniques to enhance the atom number, the frequency stability of any atomic fountain clock, already established as primary frequency standard, may be improved without opening its vacuum chamber.
We
studied the effects
of surface morphology and carrier distribution
of α-Fe2O3 electrodes on the enhancement
of water electrolysis under microwave (MW) irradiation. We deposited
α-Fe2O3 electrodes with various morphologies
on Nb-doped rutile TiO2 (100) substrates. α-Fe2O3 films with rough and flat surfaces were deposited
using electrodeposition (ED) and pulsed laser deposition (PLD), respectively.
The ED α-Fe2O3 film showed a larger response
to the MW electric field applied to the electrodes than did the PLD
film. In addition, the response was linearly correlated with the MW
electric field intensity. Using scanning MW microscopy, we found that
the local MW susceptibility of the α-Fe2O3 electrode was enhanced at the grain boundary of the ED α-Fe2O3 film. Analysis of the surface band structure
of both ED and PLD α-Fe2O3 films using
electrochemical impedance spectroscopy showed that the ED α-Fe2O3 film had a wider depleted layer, indicating
increased accumulation of holes on the surface of the electrode to
enhance water oxidation. We concluded that the accumulation of holes
at the grain boundary of the ED α-Fe2O3 film determines the enhancement of water oxidation under an MW electric
field.
We describe the preliminary evaluation of the frequency corrections and their uncertainty in the cesium fountain primary frequency standard (PFS) NMIJ-F2 under development at National Metrology Institute of Japan (NMIJ). In NMIJ-F2, cold atoms generated from a vapor-loaded optical molasses in the (001) configuration are optically pumped to the Zeeman sublevels of m F = 0 to increase the number of atoms involved in the Ramsey interrogation. Moreover, a cryocooled sapphire oscillator with ultralow phase noise is employed as the local oscillator to avoid degradation of the frequency stability due to the Dick effect. As a result, we have obtained a very high fractional frequency stability of 9.7 × 10 −14 τ −1/2 . As for systematic frequency shifts, the fractional correction for the second-order Zeeman shift is experimentally estimated to be (−165.5 ± 0.5) × 10 −15 from the first-order Zeeman shift of atoms in m F = +1 launched to various heights. The fractional frequency correction for cold-atom collisions is estimated to be (+3.3 ± 0.4) × 10 −15 by extrapolating the frequency to zero density from the frequencies measured for various nonzero atom numbers. We will soon be able to make a comparison with other atomic fountain PFSs at the 1 × 10 −15 level.Index Terms-Atomic fountain clock, primary frequency standard (PFS), uncertainty evaluation.
In this study, we demonstrate the temperature dependence of the dielectric properties of Al 2 O 3 and Ba 2 Ti 9 O 20 ceramics, using a probe-backside reflection (PBR) method, at frequencies range up to 320 GHz. The impact of transmission loss on the dielectric properties was first eliminated from the measured S-parameter values using the original S-parameter values of a transmission line. Although the temperature coefficient of dielectric permittivity was uncertain owing to limitations in the measurement repeatability of the PBR method, those of loss tangents of Al 2 O 3 and Ba 2 Ti 9 O 20 ceramics were calculated as 2.8 × 10 −5 K −1 and 1.1 × 10 −4 K −1 , respectively, for frequencies up to 125 GHz. Furthermore, the temperature coefficient of the dielectric permittivity of Al 2 O 3 was calculated as 691 ppm K −1 at 255 GHz, while those of the dielectric loss tangent at 235 GHz and 275 GHz was calculated as 1.2 × 10 −5 K −1 and 1.5 × 10 −5 K −1 , respectively.
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