Research at the University of Strathclyde on geomagnetic sensors has resulted in a succession of highly sensitive scalar instruments. The latest of these, exploiting free-induction-decay optically pumped magnetometer (FID-OPM) techniques achieves 200 fT.Hz-1/2 in Earth’s field and is self-calibrating, with instrumental drift below 10 pT over long timescales (10 ks+). As such it is an enabling technology for magnetic survey imaging and measurement of geomagnetic transients at unprecedented levels of resolution. Realising these benefits in practice by development and deployment of a field-portable FID-OPM is now feasible. The PhD research proposed will carry out this development, and, with AWE, quantify new capabilities across a range of key challenges. The project will progress through three interlinked aspects of parallel development on the FID-OPM

–           Hardware design, build and laboratory validation: the FID-OPM can be realised in a field package using microfabricated alkali vapour cells (available at Strathclyde through ongoing development work), chip-scale VCSEL lasers, high-performance analogue electronics for signal acquisition and laser control, and efficient scalable digital signal processing. By contrast with a spin maser OPM, the FID-OPM does not require firmware level FPGA programming, and so the student will, through close working with experts in each of these, build FID-OPM sensors at TRL5/6. Strathclyde’s facilities in optical and magnetic precision testing will allow these devices to be fully characterised in the lab.

–           Fundamental optimisation of the FID-OPM operation mode: FID-OPMs achieve ultra-high accuracy and precision because they exploit precise and controlled state preparation in the alkali sample. This unlocks fundamental physical processes known as light-narrowing, which are the key to the performance of the device. The interplay between these processes, sublevel dynamics and measurement systematics is a rich and valuable field for scientific enquiry, for which the student will, using both the portable devices and laboratory-scale controlled experimentation, complete and publish high-impact academic research on these topics. Deepening understanding on these will also drive development of higher performance in next-gen field devices.

–           Use-case-led demonstration, evaluation and system integration: the FID-OPM is an intentionally disruptive technology and it is not at this point clear which of the use-cases that it can be applied to will benefit most from the accuracy and precision enhancement it offers. Having a fieldable demonstration system offers the great advantage of allowing testing across use cases, and in this the academic team will work closely with technical authorities at AWE in forming meaningful test plans, running field evaluations and developing system requirements and interfaces (such as integration with GPS and non-GPS data registration) from the outset of the project.