Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.658864
Title: Beamshaping and fluorescent enhancement from nanostructures and arrays
Author: Stokes, Jamie Lee
ISNI:       0000 0004 5356 693X
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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Abstract:
This thesis presents novel results in the field of light manipulation for the purpose of improving lasing in the mid-infrared. It presents comprehensive studies that encompass the design, fabrication, testing and characterisation of nano and microscale plasmonic nanostructures. The main aim of the work is to incorporate nanostructures directly onto the emitting facet of mid-infrared lasers during their fabrication process. The purposes of the structures are to collimate, focus or shape the beam profile of the lasers whilst simultaneously modifying the lasers properties by selecting appropriate feedback radiation reflected into the laser. The thesis introduces the reader to the state of the art in the field of plasmonic nanostructures and the mid-infrared technologies. It then guides the reader through the required background theory before introducing the finite-difference time-domain method, the author's preferred method of simulating nanostructures. Methods of fabricating plasmonic nanostructures are then discussed before as-step Focussed Ion Beam (FIB) milling technique is introduced that can be used for reliable fabrication of features on the nanometer scale (~30nm). A systematic and comprehensive study is presented in chapter 4 of plasmonic nanoantennas. The strong dependency of nanoantennas optical properties on their geometries is explored alongside how they resonantly enhance point-like dipole source emissions. The work then continues to investigate dual resonant plasmonic structures that have the potential to resonantly enhance both the absorption and emission of point-like emitters such as quantum dots and dye molecules. Nanoantenna arrays are then introduced and are designed for the purpose of fluorescent enhancement and focussing in chapter 4. The chapter then presents the successful fabrication process of the nanoantenna arrays and introduces the experimental setups and equipment used to test and characterise them. An analytical model to predict the beamshape of plasmonic nanoantenna arrays is developed and compared to measurements. The comparison shows an extremely good agreement, demonstrating that plasmonic beamshaping has occurred. This chapter also presents a novel way of measuring field enhancement in the presence of both focussing effects and Purcell enhancement. An overall, measured field enhancement of ~50,OOOX is shown in the presence of a plasmonic nanoantenna array. Finally the thesis investigates plasmonic gratings that can be more reliably fabricated as potential lenses for the mid-infrared wavelength region. A standalone lens is shown to collimate laser light and the results are supported by simulation. Chapter 6 then finishes by demonstrating the possibilities of modal selection when fabricated onto the facet of a laser. In this section the 4th TE mode is selected to be reflected back into the laser to undergo gain and become dominant and the measured results are again, predicted by simulation .
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.658864  DOI: Not available
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