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- PublicationAccès libre3D printed microwave cavity for atomic clock applications: proof of conceptThe authors present the realisation and characterisation of an additively manufactured (AM) microwave resonator cavity for double-resonance (DR) vapour-cell atomic clocks. The design of the compact microwave cavity is based on the loop-gap resonator approach, previously demonstrated for conventionally-machined aluminium components. In the present study, the resonator is fabricated by AM using a metal-coated polymer. A resonance frequency at the desired 6.835 GHz rubidium atomic frequency is obtained. When employed in an atomic clock setup, the AM cavity enables a DR signal of <;500 Hz linewidth and of nearly 20% contrast, thus fulfilling the stringent requirements for DR atomic clocks. A clock short-term stability of 1 × 10 -12 τ -1/2 is demonstrated, comparable to state-of-the-art clock performances.
- PublicationMétadonnées seulementThe Micro Loop-Gap Resonator: A Novel Miniaturized Microwave Cavity for Double-Resonance Rubidium Atomic ClocksNowadays mobile and battery-powered applications push the need for radically miniaturized and low-power frequency standards that surpass the stability achievable with quartz oscillators. For the miniaturization of double-resonance rubidium ( 87 Rb) atomic clocks, the size reduction of the microwave cavity or resonator (MWR) to well below the wavelength of the atomic transition (6.835 GHz for 87 Rb) is of high interest. Here, we present a novel miniaturized MWR, the μ-LGR, for use in a miniature DR atomic clock and designed to apply a well-defined microwave field to a microfabricated Rb cell that provides the reference signal for the clock. This μ-LGR consists of a loop-gap resonator-based cavity with very compact dimensions (<;0.9 cm 3 ). The μ-LGR meets the requirements of the application and its fabrication and assembly can be performed using repeatable and low-cost techniques. The concept of the proposed device was proven through simulations, and prototypes were successfully tested. Experimental spectroscopic evaluation shows that the μ-LGR is well-suited for use in an atomic clock. In particular, a clock short-term stability of 7 × 10 -12 τ -1/2 was measured, which is better than for other clocks using microfabricated cells and competitive with stabilities of compact Rb clocks using conventional glass-blown cells.
- PublicationAccès libreMicrofabricated alkali vapor cell with anti-relaxation wall coatingWe present a microfabricated alkali vapor cell equipped with an anti-relaxation wall coating. The anti-relaxation coating used is octadecyltrichlorosilane and the cell was sealed by thin-film indium-bonding at a low temperature of 140 °C. The cell body is made of silicon and Pyrex and features a double-chamber design. Depolarizing properties due to liquid Rb droplets are avoided by confining the Rb droplets to one chamber only. Optical and microwave spectroscopy performed on this wallcoated cell are used to evaluate the cell’s relaxation properties and a potential gas contamination. Double-resonance signals obtained from the cell show an intrinsic linewidth that is significantly lower than the linewidth that would be expected in case the cell had no wall coating but only contained a buffer-gas contamination on the level measured by optical spectroscopy. Combined with further experimental evidence this proves the presence of a working anti-relaxation wall coating in the cell. Such cells are of interest for applications in miniature atomic clocks, magnetometers, and other quantum sensors.
- PublicationMétadonnées seulementBarometric Effect in Vapor-Cell Atomic ClocksVapor-cell atomic clocks are compact and high-performance frequency references employed in various appli-cations ranging from telecommunication to global positioningsystems. Environmental sensitivities are often the main sourcesof long-term instabilities of the clock frequency. Among thesesensitivities, the environmental pressure shift describes the clockfrequency change with respect to the environmental pressurevariations. We report here on our theoretical and experimentalanalysis of the environmental pressure shift on rubidium atomicfrequency standards (RAFSs) operated under open atmosphere.By using an unsealed high-performance laser-pumped rubidiumstandard, we demonstrate that the deformation of the vapor-cell volume induced by the environmental pressure changes(i.e., barometric effect) is the dominant environmental pressureshift in a standard laboratory environment. An experimentalbarometric coefficient of 8.2×10−14/hPa is derived, in goodagreement with theory and with previously reported measure-ments of frequency shifts of RAFS operated when transiting tovacuum.
- PublicationAccès libreRb vapor-cell clock demonstration with a frequency-doubled telecom laserWe employ a recently developed laser system, based on a low-noise telecom laser emitting around 1.56 μm, to evaluate its impact on the performance of an Rb vapor-cell clock in a continuous-wave double-resonance scheme. The achieved short-term clock instability below 2.5·10−13·τ−1∕2 demonstrates, for the first time, the suitability of a frequency-doubled telecom laser for this specific application. We measure and study quantitatively the impact of laser amplitude and frequency noises and of the ac Stark shift, which limit the clock frequency stability on short timescales. We also report on the detailed noise budgets and demonstrate experimentally that, under certain conditions, the short-term stability of the clock operated with the low-noise telecom laser is improved by a factor of three compared to clock operation using the direct 780-nm laser.
- PublicationAccès libreCharacterization of Frequency-Doubled 1.5-μm Lasers for High-Performance Rb ClocksWe report on the characterization of two fiber-coupled 1.5- μm diode lasers, frequency-doubled and stabilized to Rubidium (Rb) atomic resonances at 780 nm. Such laser systems are of interest in view of their implementation in Rb vaporcell atomic clocks, as an alternative to lasers emitting directly at 780 nm. The spectral properties and the instabilities of the frequency-doubled lasers are evaluated against a state-of-the-art compact Rb-stabilized laser system based on a distributed-feedback laser diode emitting at 780 nm. All three lasers are frequency stabilized using essentially identical Doppler-free spectroscopy schemes. The long-term optical power fluctuations at 780 nm are measured, simultaneously with the frequency instability measurements done by three beat notes established between the three lasers. One of the frequency-doubled laser systems shows at 780 nm excellent spectral properties. Its relative intensity noise <10−12 Hz−1 is one order of magnitude lower than the reference 780-nm laser, and the frequency noise <106 Hz2/Hz is limited by the laser current source. Its optical frequency instability is <4 × 10−12 at τ = 1 s, limited by the reference laser, and better than 1 × 10−11 at all timescales up to one day. We also evaluate the impact of the laser spectral properties and instabilities on the Rb atomic clock performance, in particular taking into account the light-shift effect. Optical power instabilities on long-term timescales, largely originating from the frequency-doubling stage, are identified as a limitation in view of high-performance Rb atomic clocks.
- PublicationAccès libreHigh performance vapour-cell frequency standardsWe report our investigations on a compact high-performance rubidium (Rb) vapour-cell clock based on microwave-optical double-resonance (DR). These studies are done in both DR continuous-wave (CW) and Ramsey schemes using the same Physics Package (PP), with the same Rb vapour cell and a magnetron-type cavity with only 45 cm3 external volume. In the CW-DR scheme, we demonstrate a DR signal with a contrast of 26% and a linewidth of 334 Hz; in Ramsey-DR mode Ramsey signals with higher contrast up to 35% and a linewidth of 160 Hz have been demonstrated. Short-term stabilities of 1.4×10-13 τ-1/2 and 2.4×10-13 τ-1/2 are measured for CW-DR and Ramsey-DR schemes, respectively. In the Ramsey-DR operation, thanks to the separation of light and microwave interactions in time, the light-shift effect has been suppressed which allows improving the long-term clock stability as compared to CW-DR operation. Implementations in miniature atomic clocks are considered.