Near-infrared saturable and reverse saturable absorption of ion beam synthesized VO2 nanocrystals
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Date
2020-06-17
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Abstract
We investigate the nonlinear optical response of a thin film of ion-implanted VO2
nanocrystals with open aperture z-scans involving femtosecond near-infrared pulses. Beyond
the established nonlinearity related to the insulator-metal phase transition of VO2, the metallic
state features a pronounced saturable absorption for 100 fs pulses from a modelocked Yb:fiber
source at = 1036 nm. In contrast, we find a pronounced reverse saturable absorption for 90 fs
pulses in the telecom window at = 1550 nm. We attribute these nonlinearities to a transient
red-shift of the plasmonic resonance of the nanocrystals, in line with the temperature dependence
of the linear absorption and the theoretical expectation for electronic heating. Details of the
transmissivity characteristics can be tailored by the lattice temperature and/or the size of the
nanocrystals. The results hold promise for the use of VO2 nanocrystals as a saturable absorber,
e.g., to mode-locked near-infrared lasers.