Jacques Morel

All-Fiber Multi-Purpose Gas Cells and Their Applications in Spectroscopy

We demonstrate a multi-purpose all-fiber design for gas-filled cavities based on hollow core photonic crystal fibers and on a specially designed fiber connector system. The connector system allows to evacuate and to fill the fiber core with a gaseous medium and keeping it pressure-tight. It also allows connecting the hollow core fiber to standard fibers. We demonstrate the flexibility and functionality by realizing three different all-fiber spectroscopic devices. Firstly, a single pass gas cell for linear absorption spectroscopy, secondly, a double pass gas cell and, thirdly, an all-fiber Fabry-Perot cavity for nonlinear saturation spectroscopy.

All-fiber frequency-stabilized erbium doped ring laser

We present an all-fiber frequency-stabilized ring laser system with an integrated reference gas cell consisting of a hollow core fiber filled with acetylene. Through nonlinear absorption spectroscopy the laser frequency is stabilized to a specific absorption line of acetylene. Three different stabilization schemes are investigated and the minimum Allan deviation obtained after 100 s is 4.4 · 10(-11).

Pulsed erbium fiber laser with an acetylene-filled photonic crystal fiber for saturable absorption

We investigate the dynamics of an erbium-doped fiber ring laser that is equipped with an intracavity hollow core photonic crystal fiber gas cell. The cell is filled with acetylene as a saturable absorber. We observe cw operation at low pressures, Q switching at intermediate pressure levels, and mode locking at high pressures applied. Moreover, we show that the transition from the cw to the pulsed mode may be exploited for sensitive gas detection.

First investigation of the noise and modulation properties of the carrier-envelope offset in a modelocked semiconductor laser

We present the first characterization of the noise properties and modulation response of the carrier-envelope offset (CEO) frequency in a semiconductor modelocked laser. The CEO beat of an optically-pumped vertical external-cavity surface-emitting laser (VECSEL) at 1030 nm was characterized without standard f-to-2f interferometry. Instead, we used an appropriate combination of signals obtained from the modelocked oscillator and an auxiliary continuous-wave laser to extract information about the CEO signal. The estimated linewidth of the free-running CEO beat is approximately 1.5 MHz at 1-s observation time, and the feedback bandwidth to enable a tight CEO phase lock to be achieved in a future stabilization loop is in the order of 300 kHz. We also characterized the amplitude and phase of the pump current to CEO-frequency transfer function, which showed a 3-dB bandwidth of ∼300  kHz for the CEO frequency modulation. This fulfills the estimated required bandwidth and indicates that the first self-referenced phase-stabilization of a modelocked semiconductor laser should be feasible in the near future.

Measurement of the magnetic field profile in the atomic fountain clock FoCS-2 using Zeeman spectroscopy

We report the evaluation of the second order Zeeman shift in the continuous atomic fountain clock FoCS-2. Because of the continuous operation and its geometrical constraints, the methods used in pulsed fountain are not applicable. We use here time-resolved Zeeman spectroscopy to probe the magnetic field profile in the clock. The pulses of ac magnetic excitation allow us to measure the Zeeman frequency with spatial resolution and to evaluate the Zeeman shift with an uncertainty smaller than 10E-16 in relative units.

First Investigation of the Noise and Modulation Properties of the Carrier Envelope Offset Frequency in a Semiconductor Modelocked Laser

We report the first characterization of the CEO-frequency in a modelocked semiconductor laser, in terms of noise and modulation bandwidth, performed using a novel approach that does not require an octave-spanning spectrum and a self-referencing scheme.

Status and prospect of the Swiss continuous Cs fountain FoCS-2

The continuous cesium fountain clock FoCS-2 at METAS presents many unique characteristics and challenges in comparison with standard pulsed fountain clocks. For several years FoCS-2 was limited by an unexplained frequency sensitivity on the velocity of the atoms, in the range of 140 • 10-15. Recent experiments allowed us to identify the origin of this problem as undesirable microwave surface currents circulating on the shield of the coaxial cables that feed the microwave cavity. A strong reduction of this effect was obtained by adding microwave absorbing coatings on the coaxial cables and absorbers inside of the vacuum chamber. This breakthrough opens the door to a true metrological validation of the fountain. A series of simulation tools have already been developed and proved their efficiency in the evaluation of some of the uncertainties of the continuous fountain. With these recent improvements, we are confident in the future demonstration of an uncertainty budget at the 10-15 level and below.

Design and realization of a low phase gradient microwave cavity for a continuous atomic fountain clock

Recently, microwave phase gradients were identified as the main source of uncertainty in the continuous fountain clock. Indeed, because of its particular geometry with two interaction zones, a dedicated research effort was necessary to reduce this effect. With the help of 3D finite element simulations and ultra-precise machining, we report here on the design and realization of a new kind of low phase gradient microwave cavity. The proposed geometry based on a ring waveguide of rectangular cross-section has a theoretical spatial phase variation of 30 μrad over the interaction zones, which corresponds to a predicted relative frequency shift below 10-15.

Final report on EURAMET.PR-S3: Bilateral intercomparison of measurements of chromatic dispersion reference fibres between METAS (Switzerland) and VNIIOFI (Russian Federation)

This supplementary intercomparison was requested by VNIIOFI in order to establish the link with previous works, which were performed in the frame of EUROMET-PR.S1 and EUROMET-PR.S1.1. This bilateral intercomparison was carried out by using the same rules and technical procedures that were applied for the two previous studies. Measurements of the total chromatic dispersion, of the zero dispersion wavelength and of the dispersion slope were performed on two references, namely one G.652 fibre and one G.653 fibre. The measurement of the chromatic dispersion and of the dispersion slope showed a very good agreement between VNIIOFI and METAS results. The determination of the zero dispersion wavelength of the G.653 fibre showed deviations that were at the limit of the measurement uncertainty. This bilateral intercomparison allowed the VNIIOFI measurement system to be validated and also provided the link to the results of the EUROMET-PR.S1 project. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

All-fiber Fabry-Perot cavity enhanced spectroscopy of acetylene

Cavities are widely used in spectroscopy, for example to increase the absorption path and thus the detection sensitivity. With the advent of Hollow Core Photonic Crystal Fibers (HCPCF) it became possible to realize long absorption paths by using long fibres and, moreover, providing high electric field strength due to the small core diameters. In the recent past these fibres have been used to demonstrate saturation spectroscopy of acetylene [1] or stimulated Raman scattering in hydrogen [2].