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Photoinduced Metal-Like Phase of VO2 with Subns Recovery

Vanadium dioxide is a unique insulator–metal
transition
material with a near room temperature transition temperature that
is a major focus of interest in burgeoning fields such as all-optical
devices and neuromorphic computing. The photoinduced insulator–metal
transition of VO2 is of particular interest for the development
of ultrafast optical devices; however, the recovery dynamics of VO2 after a photoinduced insulator–metal transition must
be better understood. Here, the time-resolved differential transmittance
of VO2 after excitation by an ultrashort pump laser pulse
and the recovery of VO2 back to its equilibrium state are
studied. For pump laser fluences in a midfluence region, which is
found to match the midfluence region for the recently discovered photoinduced
monoclinic metal phase of VO2, a strong nonlinear change
in the differential transmittance of VO2 with fast recovery
is discovered. In the midfluence region, a 15 nm VO2 thin
film is shown to have a differential transmittance at the saturation
value of 14%, while exhibiting full recovery in less than 600 ps.
These results demonstrate that the large changes in the optical properties
of VO2 associated with its photoinduced insulator–metal
transition can recover on subns time scales, allowing for efficient
GHz speed all-optical and neuromorphic computing devices using VO2.