NONLINEAR NANOPROBES FOR CHARACTERIZING ULTRAFAST OPTICAL NEAR FIELD

Open Access
Author:
Li, Haifeng
Graduate Program:
Electrical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 25, 2011
Committee Members:
  • Zhiwen Liu, Dissertation Advisor
  • Zhiwen Liu, Committee Chair
  • Qiming Zhang, Committee Member
  • Shizhuo Yin, Committee Member
  • Siyang Zheng, Committee Member
  • William Kenneth Jenkins, Committee Member
Keywords:
  • Nanoprobes
  • Nonlinear optics
  • Ultrafast optics
  • Pulse measurement
Abstract:
With the rapid development of ultrafast optics and nanophotonics, it is crucial to measure the spatiotemporal evolution of an ultrafast optical near field in nanometer spatial and femtosecond temporal resolution with minimal perturbation. Although near-field scanning optical microscopy (NSOM) can achieve nanoscale spatial resolution and various ultrashort pulse diagnostic tools can characterize femtosecond laser pulses, yet such capability to non-invasively characterize the nanoscale characteristics of femtosecond pulses in all three spatial dimensions remains elusive. In this dissertation, we developed different types of nonlinear optical probes to characterize ultrashort optical pulses. The nonlinear optical probe is composed of three parts, a silica fiber taper, a single nanowire bonded to the end of the fiber and nonlinear nanoparticles attached on the tip of the nanowire. The optical fiber taper can be readily mounted on a mechanical stage and served as a macroscopic interface for handling and positioning control. The single nanowire bridges the dimension gap between the nanocrystals and the fiber taper, and is critical for achieving large aspect ratio and hence minimizing optical scattering and perturbation. The nonlinear nanoparticles give rise to its capability to characterize ultrashort optical pulses. The unique fusion of nanoscale and nonlinear features in developed nonlinear optical probes provides the ability of probing ultrafast optical field in complex 3D micro- and nano- structures. The demonstration of such ability is crucial for understanding the interaction of ultrafast optical fields and nanoscale systems. The fabrication processes of the nonlinear optical probes are illustrated in detail and the optical properties of the probes are investigated. Two different types of nonlinear optical probes, two-photon fluorescent nanoprobes and Second HARmonic nanoProbes (SHARP), are fabricated. Interferometric autocorrelation measurements near the focal point of an objective through two-photon fluorescent nanoprobes are presented. By replacing the two-photon fluorescent nanoparticles with second harmonic nanocrystals on the tip of optical nanoprobes, more advanced pulse characterization technique, frequency resolved optical gating (FROG), can be applied and detailed pulse profile information, including both amplitude and phase profiles, can be retrieved. The spatial resolution of SHARP is limited by the size of the nanocrystal on the tip. By employing auxiliary focused ion beam (FIB) nanomilling technique, we also fabricated SHARP containing only a single nonlinear nanocrystal. Pulse characterization near the focal point of a high numerical aperture objective by using the SHARP is demonstrated. Furthermore, ultrashort optical pulse characterization results in complex micro- or nano-structures, such as in the core region of a hollow-core photonics crystal fiber, based on collinear second harmonic generation-frequency resolved optical gating (SHG-FROG) measurements are presented. Last but not the least, preliminary ultrashort optical pulse characterization capability of the SHARP in turbid medium (diluted milk) is investigated.