PHARAO flight model: optical on ground performance tests
Ch. Delaroche, Ph. Gasc, Andria Ratsimandresy, Serge Beraud, Patrizia Torresi, Ph. Larivière, Ch Salomon, Michel Abgrall, Daniele Rovera, Igor Morić, Thomas Lévèque, B. Faure, François-Xavier Esnault, Olivier Grosjean, D. Massonnet, C. Escande, Fabrice Buffe, V. Bernard, Thomas Bömer, Stéphane Thomin, Philippe Laurent
PHARAO (Projet d'Horloge Atomique par Refroidissement d'Atomes en Orbite), which has been developed by CNES, is the first primary frequency standard specially designed for operation in space. PHARAO is the main instrument of the ESA mission ACES (Atomic Clock Ensemble in Space). ACES payload will be installed on-board the International Space Station (ISS) to perform fundamental physics experiments. All the sub-systems of the Flight Model (FM) have now passed the qualification process and the whole FM of the cold cesium clock, PHARAO, is being assembled and will undergo extensive tests. The expected performances in space are frequency accuracy less than 3.10-16 (with a final goal at 10-16) and frequency stability of 10-13 τ-1/2. In this paper, we focus on the laser source performances and the main results on the cold atom manipulation.
PHARAO (Projet d'Horloge Atomique par Refroidissement d'Atomes en Orbite), which has been developed by CNES, is the first primary frequency standard specially designed for operation in space. PHARAO is the main instrument of the ESA mission ACES (Atomic Clock Ensemble in Space). ACES payload will be installed on-board the International Space Station (ISS) to perform fundamental physics experiments. All the sub-systems of the Flight Model (FM) have now passed the qualification process and the whole FM of the cold cesium clock, PHARAO, is being assembled and will undergo extensive tests. The expected performances in space are frequency accuracy less than 3.10-16 (with a final goal at 10-16) and frequency stability of 10-13 τ-1/2. In this paper, we focus on the laser source performances and the main results on the cold atom manipulation.
Ultra-precise optical clocks in space will allow new studies in fundamental physics and astronomy. Within an European Space Agency (ESA) program, the “Space Optical Clocks” (SOC) project aims to install and to operate an optical lattice clock on the International Space Station (ISS) towards the end of this decade. It would be a natural follow-on to the ACES mission, improving its performance by at least one order of magnitude. The payload is planned to include an optical lattice clock, as well as a frequency comb, a microwave link, and an optical link for comparisons of the ISS clock with ground clocks located in several countries and continents. Within the EU-FP7-SPACE-2010-1 project No. 263500, during the years 2011–2015 a compact, a modular and robust strontium lattice optical clock demonstrator has been developed. The goal performance is a fractional frequency instability below 1 × 10 − 15 τ − 1 / 2 and a fractional inaccuracy below 5 × 10 − 17 . Here we describe the current status of the apparatus' development, including the laser subsystems. The robust preparation of cold 88 Sr atoms in a second-stage magneto-optical trap (MOT) is achieved.
The PARCS (Primary Atomic Reference Clock in Space) project is a joint NIST-JPL-University of Colorado venture aimed at placing a cesium (CS) atomic clock aboard the International Space Station (ISS). This orbiting clock will achieve high accuracy, in part due to the long Ramsey times afforded by the microgravity environment, and allow for precision tests of fundamental physics including relativity theory. As part of this effort, we are evaluating the characteristics of a prototype cold CS source based on launching atoms from an optical molasses. The apparatus described here will be used to develop other PARCS components such as the microwave cavity structure and detection systems, and to investigate two-dimensional cooling schemes for future CS fountains and space clocks.
We describe a space cold atom clock prototype and its operation on board an aircraft. We have recorded the atomic resonance in zero gravity during parabolic flights. This experiment must be considered as an essential step toward the construction of a space clock using cold atoms. In a microgravity environment, a cold atomic clock would outperform all ground-based clocks. By the year 2002, we plan to operate a cold atom clock on board the international space station. This mission is called Atomic Clock Ensemble in Space (ACES). We have also performed a preliminary accuracy evaluation of the prototype. The interrogation of the cold atoms is performed inside a TE/sub 013/ cavity. On earth, the phase variations of the field induce a relative frequency shift of about 1/spl times/10/sup -13/. Although the frequency shift is expected to strongly decrease in microgravity, this cavity does not seem suitable for a 1/spl times/10/sup -16/ frequency uncertainty.
The use of ultra-precise optical clocks in space (“master clocks”) will allow for a range of new applications in the fields of fundamental physics (tests of Einstein's theory of General Relativity, time and frequency metrology by means of the comparison of distant terrestrial clocks), geophysics (mapping of the gravitational potential of Earth), and astronomy (providing local oscillators for radio ranging and interferometry in space). Within the ELIPS-3 program of ESA, the “Space Optical Clocks” (SOC) project aims to install and to operate an optical lattice clock on the ISS towards the end of this decade, as a natural follow-on to the ACES mission, improving its performance by at least one order of magnitude. The payload is planned to include an optical lattice clock, as well as a frequency comb, a microwave link, and an optical link for comparisons of the ISS clock with ground clocks located in several countries and continents. Undertaking a necessary step towards optical clocks in space, the EU-FP7-SPACE-2010-1 project no. 263500 (SOC2) (2011–2015) aims at two “engineering confidence“, accurate transportable lattice optical clock demonstrators having relative frequency instability below 1×10−15at 1 s integration time and relative inaccuracy below 5×10−17. This goal performance is about 2 and 1 orders better in instability and inaccuracy, respectively, than today's best transportable clocks. The devices will be based on trapped neutral ytterbium and strontium atoms. One device will be a breadboard. The two systems will be validated in laboratory environments and their performance will be established by comparison with laboratory optical clocks and primary frequency standards. In order to achieve the goals, SOC2 will develop the necessary laser systems - adapted in terms of power, linewidth, frequency stability, long-term reliability, and accuracy. Novel solutions with reduced space, power and mass requirements will be implemented. Some of the laser systems will be developed towards particularly high compactness and robustness levels. Also, the project will validate crucial laser components in relevant environments. In this paper we present the project and the results achieved during the first year.
The Primary Atomic Reference Clock in Space (PARCS) project is a joint NIST-JPL-University of Colorado venture aimed at placing a Cs atomic clock aboard the International Space Station (ISS). This orbiting clock will achieve high accuracy, in part due to the long Ramsey times afforded by the microgravity environment, and allow for precision tests of fundamental physics including relativity theory. As part of this effort, we are evaluating the characteristics of a prototype cold Cs source based on launching atoms from an optical molasses. Experimental results, in conjunction with theoretical modeling of atom flux requirements, will be applied to the design and construction of a robust, space-qualified device. The apparatus described here will be used to develop other PARCS components such as the microwave cavity structure and detection systems, and to investigate two-dimensional cooling schemes for future Cs fountains and space clocks.
The purpose of the PHARAO project is to develop a new atomic clock generation in space. This clock takes advantage of the very low atomic velocities obtained by laser cooling techniques and the microgravity environment. Designing the PHARAO optical bench, which provides all the laser tools for the atomic manipulations, is a difficult task. In this paper we will give a global overview of the optical bench in term of functions, interfaces and performances. After establishing the optical parameters, which have an impact on the atomic clock performance, we present the model and software, which are used for the design and analysis of the optical system, taking into account the Gaussian laser beams. Some critical functions have been experimented and characterized to prove the model’s accuracy.