1. Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA
2. Department of Applied Physics, Stanford University, Stanford, California 94305, USA
3. Department of Chemistry, University of California, Berkeley, California 94720, USA
4. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
5. Department of Physics, University of California, Berkeley, California 94720, USA