Linear and nonlinear nano-plasmonics

This work describes the fabrication and optical characerisation of metal nanoparticles. Gold-nanoparticles fabricated by kolloidal lithography could be manipulated on a surface using an atomic force microscope (AFM). Synthetically manufactored metal nanoparticles showed the same behaviour and could be manipulated with nanometer precision over a distance larger than 100 nm.Also rotations along the axis perpendicular to the surface are possible with the same accuracy.Moreover the optical properties of nanoparticles were messured. Kolloidal lithography and electronbeam lithography were used to produce so-called bowtie antennas. Using darkfield spectroscopy the resonance of the antenna could be determined. The resonances were meassured for different feedgap sizes. The spectrum showed a redshift of the resonance when decreasing the feedgap of the antenna. Kolloidal lithography enables us to produce gold-bowtie-antennas without the use of chromium. This makes it possible to manipulate those antennas on the surface allowing the meassurement to be performed on the same antenna while varying the feedgap. These meassurements reveal two resonances. These two resonances result from the tilted sidewalls of the antennas. The longer wavelength mode forms when the two surfaceplasmons at the the glas/gold interface of each particle interact. This leads to a redshift of the mode when the feedgap decreases because the interaction of the two surface plasmons increases. The two surfaceplasmons at the gold/air interface do not interact due to the bigger separation.The last part of the thesis presents the nonlinear optical properties of an ensemble of gold nanoparticles fabricated by kolloidal lithography.The continuum generated by this ensemble consists of three parts: the first part emerged from selfphase modulation (SPM), followed by a second part resulted from Two Photon Photolumenescence (TPPL) and the third part is Second Harmonic Generation (SHG)

Nanomechanical control of an optical antenna

Resonant optical nanoantennas hold great promise for applications in physics and chemistry. Their operation relies on their ability to concentrate light on spatial scales much smaller than the wavelength. In this work, we mechanically tune the length and gap between two triangles comprising a single gold bow-tie antenna by precise nanomanipulation with the tip of an atomic force microscope. At the same time, the optical response of the nanostructure is determined by means of dark-field scattering spectroscopy. We find no unique single 'antenna resonance'. Instead, the plasmon mode splits into two dipole resonances for gap sizes on the order of a few tens of nanometres, governed by the full three-dimensional shape of the antenna arms. This result opens the door to new nano-mechanical devices, where mechanical changes on the nanometre scale control the optical properties of artificial structures