The design and testing of a laser frequency stabilisation system is presented for potential use in the LISA mission. The system is based on a National Physical Laboratory (NPL) dual-axis cubic cavity. The cavity spacer is manufactured from Corning ultra-low expansion (ULE) glass and incorporates thermo-mechanically insensitive mounting to allow compliance to LISA frequency noise power spectral density (PSD) requirements within the ESA-specified thermal and vibration noise environments. The performance of this cavity-based frequency stabilised laser has been determined by beat frequency comparison versus an NPL optical clock reference cavity. Light is propagated via fibre from this reference laser and an optical path-length stabilisation system is implemented to cancel phase noise induced in the fibre link. We have measured the thermal expansion for both axes of the cube and control the temperature where the linear thermal expansion of one bore is near zero. We have also measured the contribution to the overall frequency stability of thermal noise in a proposed 5-m fibre link between the laser and cavity. Finally, we demonstrate that a laser locked to the NPL cubic cavity meets the LISA frequency noise requirements.
Optical clocks can now achieve a higher stability and lower systematic uncertainty than the highest performance microwave atomic clocks. For a Trapped Ion Space Optical Clock (TISOC) project funded by the European Space Agency (ESA) we are developing an optical clock based on a trapped laser-cooled strontium ion for future deployment in space. In a laboratory setting, a 88Sr+ system has been shown to provide excellent performance and crucially has reduced size, mass, laser power and complexity compared to alternatives such as lattice clocks. Spaceborne optical atomic clocks will offer transformative capabilities for future science, navigation, and earth observation programmes. As a first step towards space deployment, the design used in our existing single ion clocks was employed as a baseline to develop a set of finite element models. These were used to simulate the response of the ion trap and accompanying vacuum chamber to vibration, shock and thermal conditions encountered 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 and how they have helped design a more robust prototype for experimental testing.
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