COALESCe - COmpAct Light Engines for Strontium Clocks

A large number of applications, including those in research, defence, and finance require compact optical clocks that retain
their accuracy and reliability for lower costs and footprints than existing systems. Optical clocks are capable of better
stability and lower uncertainty than the current standard of time; however, each clock requires a range of lasers with
demanding requirements specific to the atomic species at the heart of the clock. Neutral strontium is one of the most
widely used atoms. It has a key transition that must be addressed using a laser source with emission wavelength at 461nm,
power >1W and linewidth (spectral purity) <32MHz. Currently researchers must use expensive or inadequate laser
sources to meet these requirements. In this project we will meet all the above requirements of neutral strontium in a low
cost, compact system based on semiconductor disk laser (SDL) technology. The advantageous properties of SDLs for
tunable, narrow linewidth operation have previously been demonstrated in the laboratory; however, their potential to
address wavelengths of interest for optical clocks, and moreover to achieve this in a compact commercial format, have yet
to be realised. We will engineer a stabilised, narrow linewidth 922nm SDL with frequency doubling to 461nm within the
cost and volume parameters required for strontium optical clock-based systems to emerge from the research laboratory
and address applications in the field.

The following groups will be amongst the main beneficiaries of this project, with impact in the scientific community, the
economic sector, the military, and society:
Academic community working in quantum science and spectroscopy (scientific) - see 'Academic Beneficiaries'.
Nascent quantum technology industry (scientific, economic, society) - The UK has set the challenge for the
commercialisation of quantum technology. This will only be achieved through the development of a supply chain for the
key components, such as the laser systems to be developed and marketed as a result of this project. The consortium will
engage with the quantum technology community to ensure compatibility of the laser system for integration.
Satellite-free navigation (military) - Portable and accurate clocks are required to improve the navigational accuracy of
submarines, currently ~2km accuracy over 24 hours, to around 100m over months. This will be achieved with the
implementation of compact and robust optical clock systems enabled by these laser sources.
Finance sector (economic, society) - Latencies within electronic trading platforms lead to significant losses, e.g. a
microsecond of latency can lead to losses of several million $. The development of accurate, cost effective, and practical
optical clock systems, enabled by these laser sources, is expected to lead to their wide application in stock exchanges
around the world.
Collaboration and exploitation:
This project will build on the successful working relationship between the Institute of Photonics (IoP), the Fraunhofer Centre for Applied Photonics, and M Squared Lasers Ltd, and expand its scope to encompass the IoP's pioneering research in the
field of semiconductor disk lasers supported by previous and current EPSRC grants. This project will transfer the
knowledge and skills of these leading research groups to industry, strengthen industry access to an established academic
network, and thus enhance the expertise and reach of a rapidly growing UK company. Similarly, this project will expose the
academics of the IoP to the requirements of industry in a highly relevant sector, thus informing the direction of future
applied research.
This consortium will enable a UK company (M Squared) to be the first to market with a core component for quantum
technology. Following the developments in this project, M Squared will commercialise and manufacture the lasers in
Glasgow and market them via their established sales and marketing channels across Europe, Asia and the US. The
quantum technology research community has been identified as an early route for exploitation. Particularly in the UK, this
community has the parallel objective, supported by the EPSRC Quantum Technology Hub initiative, to develop commercial
quantum technology systems. The lasers developed by this consortium will form a key component of the supply chain
necessary to achieve this goal and ensure the impact of the Hubs.