A. Görlitz

The space optical clocks project: Development of high-performance transportable and breadboard optical clocks and advanced subsystems

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 Einsteins 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 1×10−15 at 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 todays 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.

A transportable optical lattice clock using 171 Yb

We present first results on the spectroscopy of the ¹S₀ → ³P₀ transition at 578nm in a transportable ¹⁷¹Yb optical lattice clock. With the Yb atoms confined in a one-dimensional optical lattice, we have observed linewidths below 200 Hz, limited by saturation broadening. Currently the system is being upgraded towards full clock operation and use of more compact and robust subsystems.

Towards Neutral-atom Space Optical Clocks (SOC2): Development of high-performance transportable and breadboard optical clocks and advanced subsystems

The use of ultra-precise optical clocks in space (“master clocks”) will allow for a range of new applications covering the fields of fundamental physics (tests of Einsteins 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 (which is based on a cesium microwave clock), 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-SPACE2010-1 project no. 263500 (SOC2) (2011-2015) will develop two “engineering confidence“, accurate transportable lattice optical clock demonstrators having relative frequency instability below 1×10 -15 at 1s 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. This paper will give an overview of the project and of the results achieved during theProject ReCover aims at developing beyond state-of-the-art service capabilities to support fighting deforestation and forest degradation in the tropical region. The service capabilities mean provision of a monitoring system of forest cover, forest cover changes, and biomass including a robust accuracy assessment. This paper presents the forest monitoring concept and the first results on Recover study sites. ReCover contributes to the efforts to reduce the errors in the estimates of the terrestrial carbon balance that result from uncertain rates of tropical deforestation. It develops methods for the REDD (Reducing Emissions from Deforestation and Forest Degradation) process by developing and implementing satellite image based methods for the monitoring of tropical forests. The REDD will be a major driver for the development of more effective and more reliable procedures for the monitoring of tropical forests. Many developing countries lack human resources and funding for detailed forest inventories. This paper reports the achievements of the first year of ReCover and the results of services in Mexico, Guyana, Democratic Republic of Congo, and Fiji. Altogether 42 products were delivered to the users of Recover. The accuracy in forest and non-forest classification was from 85 % to 91 % with one exception (76 %).

The space optical clocks project

The Space Optical Clocks project aims at operating lattice clocks on the ISS for tests of fundamental physics and for providing high-accuracy comparisons of future terrestrial optical clocks. A pre-phase-A study (2007- 10), funded partially by ESA and DLR, included the implementation of several optical lattice clock systems using Strontium and Ytterbium as atomic species and their characterization. Subcomponents of clock demonstrators with the added specification of transportability and using techniques suitable for later space use, such as all-solid-state lasers, low power consumption, and compact dimensions, have been developed and have been validated. This included demonstration of laser-cooling and magneto-optical trapping of Sr atoms in a compact breadboard apparatus and demonstration of a transportable clock laser with 1 Hz linewidth. With two laboratory Sr lattice clock systems a number of fundamental results were obtained, such as observing atomic resonances with linewidths as low as 3 Hz, non-destructive detection of atom excitation, determination of decoherence effects and reaching a frequency instability of 1×10-16.

Mass scaling in photoassociation of spin-singlet atoms

Photoassociation spectroscopy, based on forming of molecules from colliding atoms in the presence of light, is a priceless tool for the study of atomic interactions. It enables direct measurements of bound state energies, both in excited and ground state molecules. Applications include determinations of s-wave scattering lengths, as well as atomic state lifetimes. In this work we present the results of our research on the mass-scaling behaviour of molecular bound state energies and collisional properties in spin-singlet atoms. We will concentrate on two such species: strontium and ytterbium, both of which offer several stable isotopes, enabling mass tuning of the systems properties.

Development of compact lattice optical clocks towards future space clocks

Within the ELIPS 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. In this project two accurate transportable lattice optical clock demonstrators having relative frequency instability below 1×10-15 at 1 s integration time and relative inaccuracy below 5×10-17 are under development. Crucial requirements are moderate volume, electrical power consumption and mass, and robustness. Furthermore, a modular concept is favourable.

A compact source of ultracold ytterbium for an optical lattice clock

In this paper, we present the development of a compact source of ultracold Yb atoms for an optical lattice clock. All laser systems that are required for the operation of the compact source are based on diode lasers. We have already implemented the first cooling stage using laser diodes at 399nm and could realize a magnetooptical trap of 174Yb with 3 × 107 atoms.