RESUMO
Direct far-field visualization and characterization of surface plasmon polaritons (SPPs) are of great importance for fundamental studies and technological applications. To probe the evanescently confined plasmon fields, one usually requires advanced near-field techniques, which is typically not applicable for real-time, high-throughput detecting or mapping of SPPs in complicated environments. Here, we report the utilization of rare-earth-doped nanoparticles to quantitatively upconvert invisible, evanescently confined SPPs into visible photoluminescence emissions for direct far-field visualization of SPPs in a complicated environment. The observed interference fringes between the SPPs and the coherent incident light at the metal surface provide a quantitative measurement of the SPP wavelength and the SPP propagating length and the local dielectric environments. It thus creates a new signaling pathway to sensitively transduce the local dielectric environment change into interference periodicity variation, enabling a new design of directly measurable, spectrometer-free optical rulers for rapid, ultrasensitive label-free detection of various biomolecules, including streptavidin and prostate-specific antigen, down to the femtomolar level.
RESUMO
This paper discusses the influence of the setup on the measurement reliability and reproducibility for the secondorder inter-modulation distortion (IMD2) generated in RF BAW duplexers. Our measurement results show that the IMD2 level can be reliably and reproducibly measured when the port terminations are properly applied. For example, a filter and a relatively large (>20 dB) attenuator are necessary between an oscillator and the antenna port of the duplexer to suppress the nonlinear mixing and the impedance mismatching. If the order of these two devices were reversed, the IMD2 level would change significantly. Although an isolator is commonly used to stabilize the power amplifier output, our research results show that not using an ISO produced more accurate results.