Paul-Eric Pottie

Three-dimensional cooling of cesium atoms in a reflecting copper cylinder

We present what is to our knowledge the first observation of spin-polarized atoms cooled within a reflecting cylinder in a high-power medium. A low-pressure vapor of cesium atoms is stored in a glass cell whose volume is 58 cm(3). Cooling laser light (lambda=852 nm) is injected into the cell by optical fibers and is recycled by multiple reflections from the walls of the cylinder. The technique used in this experiment greatly simplifies the generation of laser-cooled atoms. A maximum of 2.5 x 10(8) cold atoms was detected by a time-of-flight technique. The damping of atomic motion has lead to temperatures as low as 3.5muK .

Ultrastable optical frequency dissemination on a multi-access fibre network

We report a laboratory demonstration of the dissemination of an ultrastable optical frequency signal to two distant users simultaneously using a branching network. The ultrastable signal is extracted along a main fibre link; it is optically tracked by a narrow linewidth laser diode, which light is injected in a secondary link. The propagation noise of both links is actively compensated. We implement this scheme with two links of 50-km fibre spools, the extraction being set up at the mid-point of the main link. We show that the extracted signal at the end of the secondary link exhibits a fractional frequency instability of 1.4xa0×xa010−15 at 1-s measurement time, almost equal to the 1.3xa0×xa010−15 instability of the main link output end. The long-term instabilities are also very similar, at a level of 3–5xa0×xa010−20 at 3xa0×xa0104-s integration time. We also show that the setting up of this extraction device, or of a simpler one, at the main link input, can test the proper functioning of the noise rejection on this main link. This work is a significant step towards a robust and flexible ultrastable network for multi-users dissemination.

HORACE: atomic clock with cooled atoms in a cell

Our aim is to use cold atoms not for reducing instability or inaccuracy in the range of 10/sup -16/ or better, but to use them for reducing the size of atomic clocks. The key idea of HORACE is to fold in a microwave cavity every zone of the atomic resonator of a standard clock: zones of cooling and atomic preparation, zone of interrogation and zone of detection. Then the cell of HORACE has to be a microwave cavity as well as an optical cavity. Thus cooling of cesium atoms can only be obtained by isotropic cooling light generated inside it. In this paper, we first expose the main features of HORACE and two different configurations. Metrological aspects as well as the way the atoms would be efficiently cooled are then developed. A preliminary validation of HORACE is also demonstrated.

Hybrid optical link for ultra-stable frequency comparison

We present a hybrid fiber link to realize the local two-way optical frequency comparison with self-synchronization. It enables us to detect round-trip fiber noise and one-way fiber noise, and estimate the residuals. Moreover, we can check, to the best of our knowledge for the first time, the reciprocity of the accumulated noise forth and back over a bi-directional fiber, and also evaluate the noise correlation between two adjacent fibers with the hybrid setup.

Frequency comb-assisted QCL stabilization for high resolution molecular spectroscopy

We present a frequency comb-assisted experimental setup which enables us to both coherently transfer the stability and accuracy of a remote near-infrared (NIR) ultrastable laser to a mid-infrared (MIR) quantum cascade laser (QCL), and widely tune the QCL frequency for spectroscopic applications. The QCL is stabilized at the level of 2×10−15 from 1 to 100 s, with an accuracy of 10−14 after 100 s. The achievable frequency tuning paves the way for high-resolution saturated absorption spectroscopy of molecular transitions, in particular in spectral regions that were previously inaccessible with standard stabilized MIR lasers. Preliminary results show a sensitivity at the kHz level on transition center frequencies.

Time and frequency transfer over a 500 km cascaded White Rabbit network

We perform experiments with White Rabbit for time and frequency dissemination over long distance optical fiber links. We consider a unidirectional link setup to ensure compatibility with active telecommunication networks and build the first four-span 500 km cascaded White Rabbit link, using commercial White Rabbit equipment and improved software parameters. We demonstrate a frequency transfer stability at the level of 2 × 10−15 at 200 000 s of integration time. The time transfer stability reaches a minimum of 1.2 ps at 20 seconds of integration time. Finally, we compare our results with infield applications and discuss the limitations of the performance.

Progress on the REFIMEVE+ project for optical frequency standard dissemination

High-resolution time and frequency transfer between remote laboratories are of major interest for many fundamentals applications, such as tests of general relativity or temporal variation of fundamental constants performed by comparing clocks signals. We report on the progress of a metrological fiber network on the French territory, with extensions to Europe, which aims to provide an ultra-stable frequency signal to around 20 laboratories. This network is based on the dissemination of an ultra-stable signal using optical links through the academic fiber internet network. As a first step, we have demonstrated robust links of up to 1480 km with stability at 104 s and accuracy below 10−19.

CLONETS - clock network services: Strategy and innovation for clock services over optical-fibre networks

Methods for long-distance time and frequency transfer over optical fibers have demonstrated excellent performances and are evolving rapidly. CLONETS is a European Union-funded coordination and support action intended to facilitate the vision of a sustainable, pan-European optical fiber network for precise time and frequency reference dissemination.