31 research outputs found
Reducing cavity-pulling shift in Ramsey-operated compact clocks
We describe a method to stabilize the amplitude of the interrogating
microwave field in compact atomic clocks working in a Ramsey approach. In this
technique, we take advantage of the pulsed regime to use the atoms themselves
as microwave amplitude discriminators. Specifically, in addition to the
dependence on the microwave detuning, the atomic signal after the Ramsey
interrogation acquires a dependence on the microwave pulse area (amplitude
times duration) that can be exploited to implement an active stabilization of
the microwave field amplitude, in a similar way in which the Ramsey clock
signal is used to lock the local oscillator frequency to the atomic reference.
This stabilization results in a reduced sensitivity of the clock frequency to
microwave amplitude fluctuations that are transferred to the atoms through the
cavity-pulling effect. The proposed technique is then effective to improve the
clock stability and drift on medium and long term. We demonstrate the method
for a vapor-cell clock working with a hot sample of atoms but it can be
extended to cold-atom compact clocks.Comment: Accepted for publication by IEEE UFFC on April 16th 201
Measurement of the Blackbody Radiation Shift of the 133Cs Hyperfine Transition in an Atomic Fountain
We used a Cs atomic fountain frequency standard to measure the Stark shift on
the ground state hyperfine transiton frequency in cesium (9.2 GHz) due to the
electric field generated by the blackbody radiation. The measures relative
shift at 300 K is -1.43(11)e-14 and agrees with our theoretical evaluation
-1.49(07)e-14. This value differs from the currently accepted one
-1.69(04)e-14. The difference has a significant implication on the accuracy of
frequency standards, in clocks comparison, and in a variety of high precision
physics tests such as the time stability of fundamental constants.Comment: 4 pages, 2 figures, 2 table
Frequency transfer via a two-way optical phase comparison on a multiplexed fiber network
We performed a two-way remote optical phase comparison on optical fiber. Two
optical frequency signals were launched in opposite directions in an optical
fiber and their phases were simultaneously measured at the other end. In this
technique, the fiber noise was passively cancelled, and we compared two optical
frequencies at the ultimate 1E-21 stability level. The experiment was performed
on a 47 km fiber that is part of the metropolitan network for Internet traffic.
The technique relies on the synchronous measurement of the optical phases at
the two ends of the link, that is made possible by the use of digital
electronics. This scheme offers several advantages with respect to active noise
cancellation, and can be upgraded to perform more complex tasks
Loaded microwave cavity for compact vapor-cell clocks
Vapor-cell devices based on microwave interrogation provide a stable
frequency reference with a compact and robust setup. Further miniaturization
must focus on optimizing the physics package, containing the microwave cavity
and atomic reservoir. In this paper we present a compact cavity-cell assembly
based on a dielectric-loaded cylindrical resonator. The structure accommodates
a clock cell with inner volume and has an outer volume
of only . The proposed design aims at strongly reducing
the core of the atomic clock, maintaining at the same time high-performing
short-term stability (
standard Allan deviation). The proposed structure is characterized in terms of
magnetic field uniformity and atom-field coupling with the aid of
finite-elements calculations. The thermal sensitivity is also analyzed and
experimentally characterized. We present preliminary spectroscopy results by
integrating the compact cavity within a rubidium clock setup based on the
pulsed optically pumping technique. The obtained clock signals are compatible
with the targeted performances. The loaded-cavity approach is thus a viable
design option for miniaturized microwave clocks.Comment: Submitted to IEEE-UFF
Planar-Waveguide External Cavity Laser Stabilization for an Optical Link with 1E-19 Frequency Stability
We stabilized the frequency of a compact planar-waveguide external cavity
laser (ECL) on a Fabry-P\'erot cavity (FPC) through a Pound-Drever-Hall scheme.
The residual frequency stability of the ECL is 1E-14, comparable to the
stability achievable with a fiber laser (FL) locked to a FPC through the same
scheme. We set up an optical link of 100 km, based on fiber spools, that
reaches 1E-19 relative stability, and we show that its performances using the
ECL or FL are comparable. Thus ECLs could serve as an excellent replacement for
FLs in optical links where cost-effectiveness and robustness are important
considerations
Rabi resonances in the Λ excitation scheme
We consider the interaction of a three-level system with phase-modulated resonant fields in the Λ excitation scheme. We treat theoretically the case of a sinusoidal phase modulation, a phase step perturbation, and a stochastic phase modulation. The appearance of a Rabi resonance both in the spectrum of the optical transmitted signal (electromagnetically induced transparency) and in the spectrum of the microwave emission (coherent population trapping maser) is considered in detail. All the theoretical results are compared with the analogous ones reported for the two-level system and with our experimental observations obtained for the case of rubidium in a buffer gas
Propagation and density effects in the coherent-population-trapping maser
The coherent microwave emission from an optically thick atomic ensemble in a cavity under coherent population trapping is analyzed. Transient and continuous operations are theoretically examined within the frame of a closed three-level system in the Dicke regime. The effects related to the atomic density and to the propagation in the active medium are examined with particular reference to the subnatural linewidth, the low group velocity and the shifts of the maser emission profile from the unperturbed atomic transition. The case of alkali-metal atoms submitted to a Î excitation scheme is addressed in view of applications in the atomic frequency standard field. Experimental observations in agreement with the theoretical predictions are reported for the case of rubidium in a buffer gas. Apparent superluminal propagation is also reported and briefly discussed