Spectroscopic characterization of optically trapped semiconductor nanowires and nanoparticles

Abstract

In this thesis I describe a number of novel techniques of combining dynamic optical tweezers with spectroscopic modalities to provide important information about optically trapped nanoscale objects. These include: (i) the use of synchronous beam steering and position sensing to provide absolute position calibration of particle motion; (ii) the incorporation of micro-photoluminescence ( -PL) spectroscopy with optical tweezers to characterize the direct PL properties of trapped semiconductor nanowires, such as intensity quenching; (iii) the use of the tweezers beam as a nonlinear photo-excitation source for studying parametric and nonparametric processes in optically active materials; (iv) the incorporation of confocal arrangement with dynamic position control to map the crystal phase transition and equilibrium trapping position along the trapped nanowires. Besides, I present two suits of modeling methods for standard Holographic Optical Tweezers (HOTs) system to calculate the beam information for optical trapping and excitation of trapped nanoscale object. These include: (i) the use of Zernike polynomials phase mask to theoretically tailor optical beam shape and simulate system aberration. (ii) the incorporation of Mie scattering, dipole force calculation and beam calculation to simulate the trapping force for nanoparticles with materials of Au, InP, InSb and Si.