Announcement: Rashid Zia, Doctoral Defense
zia at stanford.edu
Wed Apr 27 15:12:33 PDT 2005
I will be defending my dissertation this Friday morning. Please attend if you are interested.
Department of Electrical Engineering
University Ph.D. Dissertation Defense
Speaker : Rashid Zia (Advisor : Prof. Mark L. Brongersma)
Title : “Resolving the Subwavelength Transport of Light: Surface Polariton Optics and Near-Field Microscopy”
Date : April 29, 2005
Time : 9:30am (Refreshments at 9:15am)
Place : Packard, Room 101
For over three hundred years, the optical microscope has provided scientists with a uniquely intuitive tool for observing microscopic biology, chemistry, and physics. Unfortunately, the resolution of conventional optical imaging is limited by diffraction and uncertainty to roughly half the wavelength of light /2n). This diffraction limit also restricts the ( optical components which have enabled the telecommunicationsminimum size of integrated revolution. Not surprisingly, there has been significant effort devoted to circumventing the diffraction limit for both optical characterization and photonic devices. In the past two decades, the scanning near-field optical microscope (SNOM) has been developed to image samples with subwavelength resolution,  and more recently, the coupling of light to surface polaritons has been suggested as a method to realize subwavelength optical circuits.  Such research not only promises to enable unparalleled control over light-matter interactions at the nanoscale, but also provides a unique regime in which to reexamine the fundamental principles of optical physics. To illustrate the potential of nanophotonics and near-field optics, two related studies on surface polariton optics and near-field microscopy will be reviewed.
Surface Polariton Optics: Guiding Light with Metal
Surface plasmon-polaritons and surface phonon-polaritons have received much attention for their ability to guide electromagnetic energy at optical and infrared frequencies, respectively. It has been suggested that surface polariton modes are not diffraction limited, and specifically, that surface plasmon modes supported by metal stripe waveguides are inconsistent with a ray-optics interpretation of guided wave phenomena. However, we have recently derived solutions for the plasmon modes which suggest an interpretation consistent with conventional waveguide theory,  and we present a dielectric waveguide model for guided polariton optics.  Leveraging this physical model, we have designed a variety of plasmonic devices analogous to dielectric integrated optical components. To substantiate a diffraction limit for surface polaritons, we present near-field images of these structures obtained by photon scanning tunneling microscopy (PSTM).
Near-Field Microscopy: Probing Optical Fields
Despite the continued improvement of near-field optical instrumentation, the interpretation of SNOM/PSTM images remains a complex process. One must deconvolve the effects of probe-sample interactions from an image to develop a precise, quantitative analysis of acquired data. Moreover, as object dimensions become significantly smaller than the wavelength of light, the conventional interpretation of near-field images as measurements of the localized light intensity breaks down. For light confined by sub-wavelength structures, we have shown that PSTM measurements are complicated by the preferential sensitivity of near-field probes to particular field components and spatial frequencies.  However, through a novel formulation of the probe’s response function, we demonstrate that preferential scattering from the near-field can be predicted and, thus, that individual components of electromagnetic waves can be imaged with subwavelength resolution in the near-field. 
 E. Betzig and J. K. Trauhnan, Science 257 (1992), 189.
 W. L. Barnes, A. Dereux, and T. W. Ebbesen, Nature 424 (2003), 824.
 R. Zia, M.D. Selker, and M.L. Brongersma. Phys. Rev. B 71 (2005), 165431.
 R. Zia, A. Chandran, and M.L. Brongersma. To be appear in Opt. Lett. 30 (2005).
 R. Zia, J. A. Matteo, L. Hesselink, and M. L. Brongersma, Near-Field Optics Conf. (Seoul: 2004).
 R. Zia, J. A. Matteo, L. Hesselink, and M.L. Brongersma. In preparation.
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