We have preformed femtosecond time-resolved and nanometer spatially resolved measurements of the photo-excited insulator to metal transition (IMT) in Vanadium Dioxide (VO2). This work was made possible by several technical advances made by the authors including the development of a nano-imaging technique that is compatible with pulsed laser sources, which is guaranteed to be artifact free . Additionally the authors have combined the Pharos Yb:kGW solid state laser system, which operates at relatively low repetition rates (750 kHz) with a commercial microscope from Neaspecc. This laser system provides the intense pumping that is required to photo-excite the IMT in VO2 and provides extremely broad spectral coverage for probing the IMT (660-20,000 nm). Using these technological advances the authors have obtained femtosecond time-resolved nano-imaging data on VO2, which are guaranteed to be artifact free. our findings expose that the non-equilibrium photo-induced IMT is highly inhomogeneous. The authors are able to extract the length scale of emergent metallic domains as a function of time-delay between the pump and probe channels to provide insight into the mechanisms of growth. Furthermore, by monitoring the monoclinic phonon with nanometer spatial resolution and femtosecond temporal resolution the authors are able to provide insight into the role that the monoclinic to rutile structural transition plays in the IMT. Our advances pave a pathway to study a wide range of systems with nanoscopic spatial, and ultrafast temporal resolution.
 A. Sternbach et al., "Artifact free time resolved near-field spectroscopy" Optics Express 25 (23), 28589-28611 (2017)
Aaron Sternbach, "Time-resolved near-field investigation of the insulator to metal transition in vanadium dioxide (Conference Presentation)," Proc. SPIE 10638, Ultrafast Bandgap Photonics III, 106380U (Presented at SPIE Defense + Security: April 17, 2018; Published: 14 May 2018); https://doi.org/10.1117/12.2315512.5783262013001.
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