| dc.description.abstract | In this thesis, plasmonically enhanced local electromagnetic (EM) field and chiral polarization manipulation in random and isolated nanoparticles are studied. Based on extinction spectrum measurement, generalized multi-particle Mie (GMM) scattering simulation, super-resolved four wave mixing (FWM), and digitized chromatic space, one had dug out plasmonically modal distribution, resonant wavelength shift, linear and nonlinear optical responses, polarization rotation, and the potential for nano-environment sensing.
For random structures, Na+-Ag+ ion exchanged composite glass and sputtering deposited thin films with a variety of filling fractions (FF) are studied. By controlling fabrication parameters, composite glasses with resonant wavelength ranges from 380 to 540 nm are obtained. These can be used as a series of stop band filters. As for the random films, it is found that the highest enhancement for the local EM field occurs when the FF reaches to the percolation threshold. Due to the property of self-similarity at percolation threshold, a single nano-interstice associated with the plasmonic hot spot over a large range can be located using the 3rd order FWM effect in far field. Besides, the position of hot spots with various resonant wavelength can be traced within a region of 120 nm × 70 nm, reflecting the mophlogical features of the film.
Regarding to isolated nanoparticle clusters, plasmonic monomer, dimer, and trimer are studied. This part research rules out the ensemble averaged effect and thereby the physical mechanisms behind can be clearly seen. For plasmonic monomer, GMM simulation is combined with digitized color space, which establishes a new nano-environment sensing method. Without utilizing spectrometer, index variation as small as 0.0021 can be resolved based on the corresponding chromaticity shift measured by a 24 bit color CCD. Compared with conventional portable spectrometers, this resolution is more than 4.8 times. In the case of plasmonic dimers, we show that this is the very fundamental unit which can generate homo optical chirality. Apart from the discussion of the origin of homo optical chirality, we also assess the capability of identifying the handedness of chiral molecules by means of the enhanced chromaticity shift. Finally, for the case of plasmonic trimmers, the manipulation of polarization at nanoscale is studied. By pumping along 2 eigen-directions in combination of optical FWM, the polarization and the output wavelength can be controlled. We successfully obtained nearly linear polarized light with extinction = 20 and elliptical light with = 2.31, demonstrating the potential of constructing nanoemitters with tunable wavelength and polarization. | en_US |