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Proceedings Paper

Optical nonlinearities and the ultrafast phase transition of VO2 nanoparticles and thin films
Author(s): Rene Lopez; Richard F. Haglund Jr.; Leonard C. Feldman; Lynn A. Boatner; Tony E. Haynes
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Paper Abstract

Z-scan and pump-probe measurements with ultra-fast 800 nm laser pulses were used to compare the ultrafast third-order optical nonlinearities of VO2 nanoparticles and thin films in both semiconducting and metallic states. It is found that when the samples are hold at temperatures above 67oC in their metallic state, both nanocrystals and thin films present a positive intensity-dependent nonlinear index of refraction. In this metallic state the nanocrystals exhibit a saturable optical nonlinearity and enhancement of the nonlinear effects larger than those found in thin films. Below the transition temperature, the optical nonlinearities are more complex, since they arise from alterations in the VO2 that arise both from the phase transition and from unrelated third-order nonlinear effects. Under these conditions, thin films exhibit a complete reversal to a negative nonlinear index of refraction while the nanocrystals, remarkably, show a smaller but still positive index. Pump-probe measurements on vanadium dioxide nanocrystals and thin films show they both exhibit an ultrafast response, undergoing the phase transition induced by a single laser shot in less than 120 fs. The speed of the solid-solid transformation, along with the striking reversal of the nonlinear properties across the phase transition, puts vanadium dioxide in a unique category among nonlinear materials.

Paper Details

Date Published: 15 February 2006
PDF: 9 pages
Proc. SPIE 6118, Ultrafast Phenomena in Semiconductors and Nanostructure Materials X, 61180O (15 February 2006); doi: 10.1117/12.640977
Show Author Affiliations
Rene Lopez, Vanderbilt Univ. (United States)
Richard F. Haglund Jr., Vanderbilt Univ. (United States)
Leonard C. Feldman, Vanderbilt Univ. (United States)
Oak Ridge National Lab. (United States)
Lynn A. Boatner, Oak Ridge National Lab. (United States)
Tony E. Haynes, Oak Ridge National Lab. (United States)

Published in SPIE Proceedings Vol. 6118:
Ultrafast Phenomena in Semiconductors and Nanostructure Materials X
Kong-Thon Tsen; Jin-Joo Song; Hongxing Jiang, Editor(s)

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