MCLAREN: Miniaturised Cold Atom Gravimeter for Space Applications

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The overall aim of the present project will be to develop a compact gravimeter demonstrator, test the gravimeters compactsubsystems for space compatibility and establish a development roadmap for space deployment. During the project criticalsubsystems will be designed and developed that will address SWaP requirements either during the project, or provide aclear path to their attainment.Addressing the limitations of current cold atom sensor designs will not only identify a route to space readiness butovercome barriers to adoption in the more immediate terrestrial gravimetry markets, and in general identify a route to makethe commercial ambitions of cold atom sensors realisable. This project will output compact and space compatiblesubsystems that can form early revenue streams including space compatible drive electronics, signal generators,miniaturised vacuum systems, fibre networks, optical architectures and wavemeters.From the specific viewpoint of the University of St Andrews, our part of this project is to exploit the interference of light for akey aspect of the proposal. The interference of light is an ubiquitous phenomenon due to its wave nature. In particular, lightpropagating in a disordered medium undergoes repeated scattering and interference, creating a "grainy" pattern known asspeckle. This is regarded as a randomization process which destroys information contained within the initial beam and isdeleterious to many optical systems. Indeed many engineers study speckle to remove its effect. Intriguingly however thereis recently growing recognition - including key observations by St Andrews - that this complex pattern is rich in usefulinformation on both the incident laser source and the environment, with startling potential uses. The aim of the St Andrewsteam is to use laser speckle and apply it to new forms of measurement and analysis that would benefit the gravimeterWe aim to demonstrate that the speckle patterns can be used to determine the wavelength of the light source. Theadvantages of using such speckle patterns are that they are complex, and can therefore embody information in a verysmall footprint, offering a departure which can supersede traditional methods for wavelength determination which use onedimensional gratings and principles of dispersion. Furthermore, this scheme obviates the need for gas cells by using thesespeckle patterns to feedback electronically to control and stabilise the output of a laser system. We would stress that verylow noise and locked laser systems are essential to operate and enable numerous cold atom technologies. In particular fora gravimeter, locking the cooling and Raman lasers at subfemtometer resolution will yield significant advances in accuracy.Coupling this with a system that is suited to ruggedisation and compactness for space based applications makes all-fibrespeckle based locking methods ideal subsystems for space based applications, and represents a step change for the field.