1. Biomedical Spectroscopy Lab, School of Physics and Astronomy, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Stoker Road, Exeter EX4 4QL, U.K.
2. Institute of Biomedical and Clinical Science, University of Exeter Medical School, Exeter, EX1 2LU, U.K.
3. Royal Devon and Exeter Hospital, Barrack Road, Exeter, EX2 5DW, U.K.
4. Central Laser Facility, Research Complex at Harwell, STFC Rutherford Appleton Laboratory, UKRI, Harwell Campus, Oxfordshire OX11 0QX, U.K.