1. Atomic and Laser Physics sub-Department, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
2. Central Laser Facility, UKRI-STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX11 0QX, UK
3. Department of Physics, University of York, Heslington, York YO10 5DD, UK
4. Department of Physics and Astronomy, White Hall Box 5315, West Virginia University, Morgantown, WV 26506-6315, USA
5. Department of Mechanical and Aerospace Engineering, University of California San Diego, 9500 Gilman Dr., La Jolla, CA 92093, USA