We report the design and in-orbit demonstration of a compact optical system for a 87Sr optical lattice clock aboard the Chinese Space Station. This system adopts a compact and robust vertically stacked architecture with a total volume of 0.11 m3 and a mass of 53.6 kg. It passed thermal and vibration qualification tests and remained fully operational after launch. In orbit, it achieved automated multi-stage laser stabilization and a blue magneto-optical trap for 87Sr atoms. This marks a significant step toward operational optical clocks in space.
We report the design and in-orbit demonstration of a compact optical system for a 87Sr optical lattice clock aboard the Chinese Space Station. This system adopts a compact and robust vertically stacked architecture with a total volume of 0.11 m3 and a mass of 53.6 kg. It passed thermal and vibration qualification tests and remained fully operational after launch. In orbit, it achieved automated multi-stage laser stabilization and a blue magneto-optical trap for 87Sr atoms. This marks a significant step toward operational optical clocks in space.
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.
A compact and robust design of an optical lattice clock with high stability and accuracy is needed for the implementation of optical clocks operating on the space station. Here, we present the proof-of-concept model of a 87Sr optical lattice clock for space constructed at the National Time Service Center. The design is different from that of a laboratorial optical clock in that it focuses on the aspects of compactness and robustness, such as the modular design, compact components, low power consumption, and all-fiber links. The physics package is placed on an aluminum alloy rack with dimensions of 40 × 55 × 28 cm3. As far as we know, this is the most compact physics package of the Sr optical clock reported. The time interleaved self-comparison frequency instability is determined to be 2.6 × 10−15/τ.
Abstract This study presents an achievement of laser cooling of alkaline-earth atoms in the Chinese Space Station’s strontium (Sr) atomic space optical clock. The system’s core components, physical unit, optical unit, and electrical unit, have a total volume of 306 L and a total mass of 163.8 kg. These compact and robust units can overcome mechanical vibrations and temperature fluctuations during space launch. The laser sources of the optical unit are composed of diode lasers, and the injection locking of slave lasers is automatically performed by a program. In the experiment, a blue magneto-optical trap of cold atoms was achieved, with the atom numbers estimated to be approximately (1.50 ± 0.13) × 10 6 for 87 Sr and (8.00 ± 0.56) × 10 6 for 88 Sr. This work establishes a foundation for atomic confinement and high-precision interrogation in space-based optical clocks and expands the frontiers of cold atom physics in microgravity.
Optical atomic clocks with precisions and accuracies in the
10−18 level [1] are now the most advanced man-made timekeeping devices. They outperform the microwave cesium atomic clocks that realize the SI definition of the second. Scaling down the size of optical atomic clocks may open the door to a range of industrial and space applications.
In this thesis, the design and preliminary results of a compact strontium cooling system are presented. In the first cooling stage, the high power 461 nm laser with 300 mW output features a modular design, while smaller laser sources for demonstrating a strontium magneto-optical trap have also been investigated. An innovative design that couples a spectroscopy cell directly into the scientific chamber reduces the overall size and power consumption of the system. Additionally, using strontium oxide as a source of strontium atoms suitable for optical clocks has achieved initial success. For the first time, a single-beam MOT configuration is applied to strontium. In this novel apparatus, the blue MOT and red MOT broadband cooling phases are able to trap 5x106 and 1000 atoms, respectively. This work shows promising progress towards developing a functional miniaturized strontium optical lattice clock.
Optical clocks are being developed worldwide and are at the forefront of frequency metrology. Today they outperform microwave clocks instability and inaccuracy by two orders of magnitude, raising discussion about the redefinition of the SI second. Their outstanding performances are paving the way to applications in different fields apart from metrology. Optical clocks can be used for geodetic measurements, such as chronometric levelling, and fundamental physics experiments. These applications require transportable, and even space-born optical clocks that are in development. Space optical clocks will serve as a high accurate references for intercontinental clock comparisons, and will also provide a unique test bench for fundamental physics theories, such as Einstein’s prediction of time dilation and equivalence principle.
This work presents the development and characterization of a transportable strontium optical lattice clock, realised in the framework of the ESA I-SOC (Space Optical Clock on the ISS) mission. The aim of the project is to investigate new technologies and techniques, in order to develop a robust apparatus as demonstrator for space applications. Special effort has been made to reduce the size and weight of the clock, so as to meet the stringent requirements of a space mission. The system reported here is one of the most compact optical clock to date, with a total volume of only 1 m3, excluding electronics.
The clock is operated with the strontium bosonic isotope 88Sr: this is preferable to the fermionic counterpart 87Sr, commonly used in optical lattice clocks, if simplicity and reliability are required. However, in terms of accuracy, bosonic clocks present some disadvantages compared with the fermionic ones, which have significantly slowed down their development for metrological applications.
We characterised the relevant operating parameters and their effect on the clock accuracy and instability. Exploiting a clock laser offering an outstanding stability, we were able to demonstrate a clock fractional instability of 3×10-18 , and an inaccuracy of 2×10-17: both values represent a factor of 30 improvement compared with previous works on bosonic optical clocks. These results suggest that, in the near future, bosonic clocks may become competitive to their fermionic counterparts. This is of interest for applications such as time scale realization, transportable clocks, or for test of fundamental physics. As an example, we measured the 88Sr-87Sr isotope shift, with an uncertainty of 12 mHz.
Optical atomic clocks demonstrate a better stability and lower systematic uncertainty than the highest performance microwave atomic clocks. However, the best performing optical clocks have a large footprint in a laboratory environment and require specialist skills to maintain continuous operation. Growing and evolving needs across several sectors are increasing the demand for compact robust and portable devices at this capability level. In this paper we discuss the design of a physics package for a compact laser-cooled 88 Sr + optical clock that would, with further development, be suitable for space deployment. We review the design parameters to target a relative frequency uncertainty at the low parts in 10 18 with this system. We then explain the results of finite-element modelling to simulate the response of the ion trap and vacuum chamber to vibration, shock and thermal conditions expected during launch and space deployment. Additionally, an electrostatic model has been developed to investigate the relationship between the ion trap geometrical tolerances and the trapping efficiency. We present the results from these analyses that have led to the design of a more robust prototype ready for experimental testing.