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Utilizing the insulator-metal phase transition of vanadium dioxide (VO2) crystal films, we develop a dual-functional sensor based on the coupling between VO2 nano-crystal films and Ag nanoparticles, which can probe fluorescence or Raman signals on the same substrate and it is switchable by changing temperature. At room temperature, the VO2 crystal films is insulator phase and the fluorescence signals of probe molecules (R6G) is detectable (Raman is in "off"). At high temperature (such as 85 °C), the VO2 crystal films become metallic phase. Ag nanoparticles interact with the metal phase of VO2 crystal films to produce stronger localized electric field. The stronger electric field can excite the Raman signals of probe molecules (R6G) and the coupled structure can also emit the Raman signals out efficiently (Raman is in "on"). The switchable probe of fluorescence and Raman signals would have potential applications in active photoelectric components, such as intelligent switch and multifunctional active sensor etc.

Wideband terahertz (THz) wave generation and detection technologies and 1550‐nm ultrafast laser technologies are presented. The usage of a 1550‐nm ultrafast fiber laser will make the THz time domain spectroscopy system a more compact one with much lower costs. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 439–443, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22165

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