1,721,051 research outputs found
Avoiding Aliasing in Allan Variance: An Application to Fiber Link Data Analysis
Full text linkOptical fiber links are known as the most performing tools to transfer ultrastable frequency reference signals. However, these signals are affected by phase noise up to bandwidths of several kilohertz and a careful data processing strategy is required to properly estimate the uncertainty. This aspect is often overlooked and a number of approaches have been proposed to implicitly deal with it. Here, we face this issue in terms of aliasing and show how typical tools of signal analysis can be adapted to the evaluation of optical fiber links performance. In this way, it is possible to use the Allan variance (AVAR) as estimator of stability and there is no need to introduce other estimators. The general rules we derive can be extended to all optical links. As an example, we apply this method to the experimental data we obtained on a 1284-km coherent optical link for frequency dissemination, which we realized in Italy
Microwave cavities for vapor cell frequency standards
No full textIn this paper, we report an analysis of the design criteria of microwave cavities for vapor cell frequency standards. Two main geometries exploited in those devices are considered: the cylindrical cavity, used, for example, in the coherent population trapping maser and in the pulsed optically pumped (POP) clock, and the spherical cavity used in the isotropically laser cooled clock. The cavity behavior is described through a lumped equivalent circuit in which the input coupling loop, the dielectric cell containing the atoms and the diodes for frequency tuning or Q control are taken into account. In particular, the effect of the cell on the cavity resonance frequency is analytically evaluated via a first-order perturbation approach. The theory is found in good agreement with the experiments performed with two different cylindrical cavities used for the POP clock; the model here developed can then be helpful in the design of the cavity system. The general principles here reported can be adapted to other standards, such as atomic fountains and hydrogen masers, and to other modes and/or geometries
Enhanced temperature sensitivity in vapor-cell frequency standards
No full textWe report on the measurement of an anomalously large temperature sensitivity of the clock frequency in a Rb cell with buffer gas. The effect is observed in a prototype of pulsed optically pumped frequency standard which allows high resolution measurements because of its frequency stability at the level 1.7 x 10^-13 for 1 s of measurement time. We attribute this phenomenon to the geometry of the interaction and to the presence in the cell of temperature inhomogeneities that may enhance the temperature sensitivity of the clock frequency via the buffer gas pressure coefficient. We also propose some solutions to reduce this unwanted effect that may limit the medium-long-term performances of highfrequency- stability vapor-cell clocks
Multistep preparation into a single Zeeman sublevel in a 87Rb vapor cell: Theory and experiment
No full textMetrological characterization of the pulsed Rb clock with optical detection
No full textWe report on the implementation and metrological characterization of a vapour-cell Rb
frequency standard working in a pulsed regime. The three main parts of the clock, physics
package, optics and electronics, are described in detail in this paper. The prototype is designed
and optimized to detect the clock transition in the optical domain. Specifically, the reference
atomic transition, excited with a Ramsey scheme, is detected by observing the interference
pattern on a laser absorption signal.
The metrological analysis includes the observation and characterization of the clock signal
and the measurement of frequency stability and drift. In terms of Allan deviation, the measured
frequency stability is as low as 1.7 × 10^−13
τ^−1/2
, τ being the averaging time, and reaches the
value of a few units of 10^−15
for τ = 10^4
s, an unprecedented result for a vapour-cell clock.
We discuss the physical effects leading to this result in this paper with particular care to laser
and microwave noises transferred to the clock signal. The frequency drift, probably related to
temperature, stays below 10−14
per day, and no evidence of flicker floor is observed.
We also mention some possible improvements that in principle would lead to a clock
stability below the 10−13
level at 1 s and to a drift of a few units of 10−15
per da
Improving short and long term stability of pulsed optically pumped vapor cell frequency standards
No full text
Laser-frequency stabilization using light shift in compact atomic clocks
Full text linkThis paper describes the light-shift laser-lock (LSLL) technique, an alternative method intended for laser-based compact atomic clocks. The technique greatly simplifies the laser setup by stabilizing the pumping-laser frequency to the same atoms involved in the clock operation, without the need of an external reference. By alternating two clock sequences, the method estimates and cancels out a controlled amount of induced light shift, acting on the laser frequency. The LSLL technique is compatible with state-of-the-art three-level clocks and was demonstrated with field-programmable-gate-array-based electronics on a pulsed-optically-pumped vapor-cell clock developed at INRIM. The results have shown that the LSLL technique operates robustly, having a capture range of gigahertz without significantly compromising clock stability. In our tests, the clock exhibited a white frequency noise of 3.2×10-13τ-1/2 for averaging times τ up to 4000 s, reaching a floor below 1×10-14 up to 100 000 s. This level of performance meets the requirements of future global navigation satellite systems on-board clocks, adding the benefits of a reduced clock footprint, as well as increased reliability and robustness
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