Nonlinear optical imaging of nanomaterials and transient absorption microscopy

Yookyung Jung, Purdue University

Abstract

Optical properties of Gold nanorods have been studied intensively for the last ten years. And the possibility of Gold nanorods as imaging agents has emerged showing strong multi-photon luminescence which has no bleaching. Despite the brightness of the multiphoton luminescence, its spectral profile is generally broad and may overlap with fluorescence from other molecules in bio-imaging study, which makes it hard to distinguish gold particles from other fluorescent molecules. On the other hand, four-wave mixing (FWM) signals from nanoparticles have narrow spectral profiles at well defined frequencies. In this work, we demonstrated the four-wave mixing from gold nanorods could be enhanced by the surface Plasmon resonance of the gold nanorods. The enhanced foru-wave mixing enabled selective imaging of nanorods in live cells. We also have demonstrated that Silicon nanowires (SiNWs) exhibit intensive fourwave mixing (FWM) and third harmonic generation (THG) emissions with a cos6è polarization dependence. These properties open up exciting opportunities for using Silicon nanowires as a novel in vivo imaging agent offering intrinsic 3D spatial resolution, high photostability, and orientation information. With the advantages of highly controllable dimensions, versatile surface chemistry and an intensive intrinsic nonlinear optical (NLO) signals. Transient-absorption spectroscopy is an established method widely used to study the electronic energy structure and energy relaxation process of materials using a pump and a probe field. In this method, the pump light perturbs the electronic states of the material and the probe light responds to the changed electronic states, resulting in a transiently enhanced or reduced absorption of the probe field compared to the case of no perturbation by the pump field. However, it is only recently that transient absorption method is applied to microscopy. And the different phase of enhanced and reduced absorption may be used as new contrast in transient absorption microscopy. In this presentation, we will demonstrate a pump-probe transient absorption microscopy method for fast, contact-free mapping of metallicity in individual single-walled carbon nanotubes (SWNTs). We employ the phase of transient absorption as a contrast to discriminate metallic and semiconducting SWNTs. Considering that the coexistence of metallic and semiconducting SWNTs as a result of synthesis has hindered their electronic and photonic applications, transient absorption microscopy will play an important role in electronic research of SWNTs. Furthermore, the strong transient absorption signal from SWNTs open up new possibilities to advance the biomedical applications of them as imaging agents in microscopy.

Degree

Ph.D.

Advisors

Cheng, Purdue University.

Subject Area

Nanoscience|Optics

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