1. Department of Applied Science and Technology (DISAT), Politecnico di Torino, C.so Duca degli Abruzzi 24, Torino, IT-10129, Italy
2. Quantum Research Laboratories and Nanofacility Piemonte, Nanoscience and Materials Division, Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, Torino, IT-10135, Italy
3. Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Albert-Einstein-Str. 7, Jena DE-07745, Germany