INSTIGATING CHIRAL-SELECTIVE NONLINEAR OPTICAL PHENOMENA IN METAMATERIALS A Thesis Presented to The Academic Faculty By Sean P. Rodrigues In Partial Fulfillment of the Requirements for the Doctoral Degree in the School of Electrical and Computer Engineering Georgia Institute of Technology August 2018 Copyright © by Sean Rodrigues 2018 i INSTIGATING CHIRAL-SELECTIVE NONLINEAR OPTICAL PHENOMENA IN METAMATERIALS Approved by: Dr. Wenshan Cai, Advisor Dr. Ali Adibi Jointly School of Electrical & School of Electrical & Computer Computer Engineering Engineering School of Materials Science & Georgia Institute of Technology Engineering Georgia Institute of Technology Dr. Vladimir Tsukruk Dr. Zhuomin Zhang School of Materials Science & School of Mechanical Engineering Engineering Georgia Institute of Technology Georgia Institute of Technology Dr. Mohan Srinivasarao School of Materials Science & Engineering Georgia Institute of Technology Date Approved: May 01, 2018 ii To my grandparents and family, Whose endless love and support made this work possible. iii ACKNOWLEDGEMENTS I would like to thank my advisor Prof. Wenshan Cai. His advocacy and his persistence in helping me to surpass my limits is more than I imagined in an advisor and I’m undeniably thankful. I’m indebted to the dedication of my labmates, Dr. Shoufeng Lan, Dr. Yonghao Cui, Dr. Lei Kang, Mohammad Taghinejad, and Zhaocheng Liu. I cannot speak enough to your guidance, support and vast knowledge of the field. Thank you so much for being there for me. A special thanks to our collaborators including Dr. Yongmin Liu, Jiahao Yan, and Prof. Shengxiang Wang. I wish the best of luck to the new graduate students Kyu-tae Lee, Lakshmi Raju, Andrew Kim, Muliang Zhu, and Dayu Zhu. I would also like to thank my thesis committee Dr. Ali Adibi, Dr. Mohan Srinivasarao, Dr. Vladimir Tsukruk, and Dr. Zhuomin Zhang for their support. I wouldn’t be in graduate school if it wasn’t for the amazing mentorship I’ve had from mentors at my alma mater: Dr. Lukas Novotny (now at ETH Zürich), Dr. Matthew Yates, Dr. James Farrar and Nicholas Valentino. Thank you to the National Science Foundation (NSF) Graduate Research Fellowship for funding me under Grant No. DGE-1148903. Thank you to the Goizueta Foundation for supporting me via the GoSTEM Fellowship for two years and Dr. Diley Hernandez for her relentless dedication to the Hispanic and Latino communities. iv Thank you to Air Force Research Labs for funding me on two separate programs, Soft Materials and Data Science, and allowing me to work at their research labs during the later summers. I want to especially thank Dr. Timothy Bunning (Chief Scientist of the Materials Research Directorate), Dr. Augustine Urbas (Optoelectronics Lead), Dr. Manuel Ferdinandus, Dr. Ben Griffin, Dr. Ekaterina Poutrina, and Dr. Dean Brown. Thank you for funding support from the Intel Foundation, the Materials Research Society, Sigma Xi, American Physical Society: Forum on Graduate Student Affairs (FGSA), IEEE Photonics. I want to also thank SPIE Cycle Outreach Grant, for allowing me to put on my workshop titled a “Day of Light.” The event was hosted in conjunction with the Hispanic and Latino College Fair 2015 and the Atlanta Day of Science (thanks to Diley Hernandez) allowing for the workshop to impact a much larger number of students than I could have reached on my own. A summary of the event can be found here: https://cos.gatech.edu/hg/item/591331 Thank you to Dr. Felicia Benton-Johnson, and Ms. Jackie Cox from CEED for making my years at GaTech so much more bearable, providing a happy and healthy environment in all the arduous days that I experienced as a graduate student. With the outmost gratitude and love for my mother, who I thank for insisting that I pursue my dreams no matter the cost. I want to thank my family, Rianna, Justin, and Joe: I may not have been physically present while I’ve been pursuing my degrees, but I’m indebted for your kindness and understanding. Finally, I want to thank all my friends for their support throughout the years. Just writing this sentence is bringing a slew of memories rushing into my v brain and with it, an enormous amount of emotion and gratitude. I feel a great deal for all of you; thank you and if I haven’t it mentioned it lately, bop me. vi TABLE OF CONTENTS ACKNOWLEDGEMENTS iv LIST OF FIGURES xi LIST OF SYMBOLS AND ABBREVIATIONS xv SUMMARY xvi FOREWORD xviii CHAPTER I. Chirality 1 1.2 Measuring Chirality 4 1.3 Chirality in Nature 7 1.4 Chirality in Metamaterials 10 1.4.1 Origin of Chirality in Metamaterials 14 1.4.2 Negative Refraction 15 1.4.3 Giant Chiral Signals 15 1.4.4 Extreme Signal Properties 17 1.4.5 Chirality for Biosensing 18 1.4.6 Nonlinear Optical Activity 19 1.4.7 Filing the Gap 20 CHAPTER II. Pertinent Nonlinear Optics 22 vii 2.1 Expansion of the Taylor Series 24 2.2 Chirality implies a lack of centrosymmetry 29 2.3 Chiral, molecular, nonlinear optics 32 2.4 Chiral Sum-Frequency Generation 33 2.5 Intensity Dependent Refractive Index 36 CHAPTER III. Nonlinear Imaging and Spectroscopy of Chiral Metamaterials 39 3.1 Design & Simulation 40 3.2 Fabrication process 42 3.3 Linear Response 45 3.4 Linear Optical Characterization 49 3.5 Second Harmonic Response 51 3.6 Imaging 58 3.7 Conclusions & Outlook 62 CHAPTER IV. Metamaterials Enable Chiral-Selective Enhancement of Two-Photon Luminescence from Quantum Emitters 63 4.1 Fabrication 68 4.2 Linear Response and Simulation 71 viii 4.3 Linear Optical characterization. 74 4.4 Imaging 76 4.5 Two photon luminescence 77 4.6 Nonlinear Characterization 79 4.7 Conclusion 87 Chapter V. Intensity-dependent modulation of optically active signals in a chiral metamaterial 89 5.1 Introduction 90 5.2 Fabrication 94 5.3 Linear Optical Response 98 5.4 Nonlinear Circular Dichroic Response 108 5.5 Nonlinear Optical Rotation 111 5.6 Conclusion 118 5.7 Recommendation 119 CHAPTER VI. Preserving Spin States upon Reflection: Linear and Nonlinear Responses of a Chiral Meta-M irror 121 6.1 Designing a Spin Maintaining Material 126 6.2 Analysis of Spin States from a Chiral Meta-mirror 132 ix 6.3 Visualizing Spin-Selective Preservation and Absorption 135 6.4 Generating chiral-responsive nonlinear signals 138 CHAPTER VII. Conclusions and Outlook 146 REFERENCES 159 x LIST OF FIGURES Page Figure 1.1: Definition of ellipticity 5 Figure 1.2: Chirality in nature: Chrysina Gloriousa 7 Figure 1.3: Metamaterial structures from the literature 11 Figure 1.4: Chiral properties of a twisted nanoarc pair in the infrared. 12 Figure 3.1: Design and simulation of the metamaterial pattern 41 Figure 3.2: Fabrication flowchart of the twisted-arc photonic metamaterial 43 Figure 3.3: Simulated transmission spectra of enantiomer A 45 Figure 3.4: Linear spectroscopy of the two enantiomers 46 Figure 3.5: Circular dichroic response 48 Figure 3.6: Linear transmission setup 50 Figure 3.7: Nonlinear spectral measurements of enantiomer A 52 Figure 3.8: Second harmonic response from enantiomer A 54 Figure 3.9: Second harmonic circular dichroism of enantiomer A 55 Figure 3.10: SHG generation dependence on pump intensity 56 Figure 3.11: Stokes polarimetry of SHG light 57 xi Figure 3.12: Transmission images of the GT logo 58 Figure 3.13: Nonlinear imaging 60 Figure 4.1: QD’s fill the volume around the metamaterial structure 66 Figure 4.2: SEM images and nanoarc patterning 67 Figure 4.3: Chiral spectral resonances for selective enhancement 71 Figure 4.4: Linear transmission images of the GT mascot 75 Figure 4.5: Emission profiles and absorption spectra for the QDs 77 Figure 4.6: Two-photon excitation profile 79 Figure 4.7: Two-photon excitation spectroscopy 81 Figure 4.8: Chirally distinct two photon luminescence 81 Figure 4.9: Two-photon luminescence – circular dichroism 85 Figure 4.10: Two-photon luminescence dependence on pump intensity 87 Figure 5.1: Schematic and micrographs of chiral metamaterial enantiomers 95 Figure 5.2: Experimental chiroptical responses for the two enantiomers 97 Figure 5.3: Optical rotation as a function of input angle 101 Figure 5.4: Orientation of linearly polarized wave incident on the chiral metamaterial 102 xii Figure 5.5: Simulations of circular dichroism and optical rotatory dispersion 106 Figure 5.6: Intensity-dependent circular dichroism 107 Figure 5.7: Powder dependent transmission at a single wavelength 111 Figure 5.8: Intensity-dependent optical rotation 112 Figure 5.9: Intensity-dependent chiral optical rotation when CD=0 116 Figure 6.1: Schematics and SEM images of the metamaterial based chiral mirror for both enantiomers 127 Figure 6.2: Schematics of the reflection behavior of the meta-mirror and a regular mirror 129 Figure 6.3: Simulated linear chiroptical responses of both enantiomers 131 Figure 6.4: Measured linear chiroptical responses of both enantiomers 133 Figure 6.5: Visualization of the chiral selective absorption and the circular polarization preservation of the meta-mirrors 137 Figure 6.6: Chiral-selective nonlinear responses from both enantiomers 139 Figure 6.7: SHG excitation spectra for enantiomers 141 Figure 6.8: Nonlinear imaging of the chiral meta-mirror 143 Figure 6.9: Creating a chiral mirror from a 3D chiral metamaterial 143 Figure 7.1: Overview of SHG study 147 xiii Figure 7.2: Overview of QD embedded chiral metamaterial 148 Figure 7.3: Overview of nonlinear optical activity study 150 Figure 7.4: Overview of chiral meta-mirror study 152 xiv LIST OF SYMBOLS AND ABBREVIA TIONS CD Circular Dichroism OR Optical Rotation SHG Second Harmonic Generation SHG-CD Second Harmonic Generation – Circular Dichroism TPL Two Photon Luminescence TPL-CD Two Photon Luminescence – Circular Dichroism NIR Near Infrared xv SUMMARY As naturally occurring chiral materials demonstrate limited circularly dichroic contrast, enhancement of these polarization dependent signals has been the focus of chiral metamaterial research.