Imaging Light with Photoelectrons on the Nano-Femto Scale

ISBN-13: 9783030528386 / Angielski / Miękka / 2021 / 132 str.

Yanan Dai

Opis

This thesis presents significant advances in the imaging and theory of the ultrafast dynamics of surface plasmon polariton fields. The author details construction of a sub-10 femtosecond and sub-10 nanometer spatiotemporal resolution ultrafast photoemission microscope which is subsequently used for the discovery of topological meron and skyrmion-like plasmonic quasiparticles. In particular, this enabled the creation of movies of the surface plasmon polariton fields evolving on sub-optical wavelength scales at around 0.1 femtosecond per image frame undergoing vortex phase evolution. The key insight that the transverse spin of surface plasmon polaritons undergoes a texturing into meron or skyrmion-like topological quasiparticles (defined by the geometric charge of the preparation) follows. In addition, this thesis develops an analytical theory of these new topological quasiparticles, opening new avenues of research, while the ultrafast microscopy techniques established within will also be broadly applicable to studies of nanoscale optical excitations in electronic materials.

Spis treści

1.0 Introduction ............................................................................................................................. 1

1.1 Collective Electron Oscillations ..................................................................................... 2

1.1.1 Plasma Model ...................................................................................................... 2

1.1.2 Localized Surface Plasmons (LSPs) .................................................................. 4

1.1.3 Surface Plasmon Polaritons (SPPs) ................................................................... 7

1.2 Techniques of Imaging Plasmon Related Phenomena .............................................. 12

1.2.1 Photoemission Electron Microscopy (PEEM) ................................................ 13

1.2.2 Low Energy Electron Microscopy (LEEM) .................................................... 17

1.2.3 Low Energy Electron Diffraction (LEED) ...................................................... 19

2.0 Experimental Methods ......................................................................................................... 21

2.1 UHV Components of LEEM/PEEM ........................................................................... 21

2.1.1 Cold Field Electron Emission Gun .................................................................. 21

2.1.2 Electron Optics .................................................................................................. 22

2.1.3 Projection Column ............................................................................................ 25

2.1.4 Apertures ........................................................................................................... 26

2.2 Sample Preparation ...................................................................................................... 27

2.2.1 Sample Stage ...................................................................................................... 27

2.2.2 Silicon Substrate Preparation .......................................................................... 28

2.2.3 Single Crystal Silver Pyramids and Wires ..................................................... 29

2.2.4 Single Crystal Silver Islands ............................................................................ 30

2.2.5 Polycrystal Silver Film ...................................................................................... 31

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2.2.6 Surface Structuring by Focused Ion Beam ..................................................... 32

2.3 Source of Photoemission .............................................................................................. 34

2.3.1 Mercury Lamp .................................................................................................. 34

2.3.2 Non-colinear Optical Parametric Amplifier (NOPA) .................................... 34

2.3.3 Interferometric Pump Probe setup.................................................................. 36

3.0 Simulation Framework ......................................................................................................... 38

3.1 Finite Difference Time Domain Algorithm ................................................................ 38

3.2 Reproduction of Static PEEM Images ........................................................................ 42

3.3 Reproduction of Time-Resolved PEEM ..................................................................... 45

3.4 Huygens Principle Algorithm ...................................................................................... 48

4.0 Propagating Surface Plasmon Polaritons (SPPs) ............................................................... 52

4.1 Propagating SPPs on Ag Wire ..................................................................................... 52

4.1.1 Co-propagation between Light and SPPs ....................................................... 52

4.1.2 Orthogonal Propagation between Light and SPPs ........................................ 56

4.2 Propagating SPPs on Ag Islands ................................................................................. 61

4.2.1 The Vectorial Nature of SPPs Coupling ......................................................... 61

4.2.2 Dynamics of the Propagating SPPs ................................................................. 65

5.0 Spin Angular Momenta and Chirality of SPPs .................................................................. 68

5.1 Spin-Angular Momentum (SAM) coupled SPPs on Ag Island ................................ 68

5.1.1 Polarization Dependent SPP Excitation and PEEM Imaging ...................... 68

5.1.2 Polarization Dependent Photoemission Yield ................................................. 76

5.1.3 Polarization Dependent SPP Phases ................................................................ 83

5.1.4 Longitudinal and Transverse Coupling of SPPs ............................................ 85

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5.2 Dynamics of Spin-Angular Momentum coupled SPPs .............................................. 88

5.3 Quantum Spin Hall Effect on Plasmonic Focusing ................................................... 92

5.3.1 Symmetrical Focus of Plasmonic Lens ............................................................ 92

5.3.2 SAM Dependent Focusing ................................................................................ 95

5.4 Focus of Chirality of SPP field .................................................................................. 101

5.4.1 Field Chirality at the Focal Point .................................................................. 101

5.4.2 Chirality Density at the Focal Point .............................................................. 104

6.0 Plasmon Orbital Angular Momentum Generation .......................................................... 108

6.1 SPP Vortex Generation by Archimedean Spirals .................................................... 109

6.1.1 Sample Design and Preparation .................................................................... 109

6.1.2 Vortex Generation with Circularly Polarized Light .................................... 113

6.1.3 In-plane Component of SPPs Vortex............................................................. 114

6.2 SPPs Vortex with Pure Geometric Charge .............................................................. 116

6.2.1 Field Evolution of SPPs Vortex Excited by Linearly Polarized Light ....... 116

6.2.2 Static PEEM imaging of SPPs Vortex ........................................................... 117

6.2.3 ITR-PEEM imaging of SPPs Vortex Dynamics ........................................... 119

6.3 The Spin Texture of the Plasmonic Vortex .............................................................. 120

6.3.1 Plasmonic Spin Texture .................................................................................. 120

6.3.2 Optical Spin Skyrmion at an SPPs Vortex Core .......................................... 125

6.3.3 Locating Optical Spin Skyrmion ................................................................... 127

7.0 Summary and Perspectives ................................................................................................ 131

Appendix A Time-Resolved PEEM Software......................................................................... 133

Appendix B Huygens Principle Simulation Package ............................................................. 138

O autorze

Yanan Dai is a postdoctoral researcher at Columbia University. He received his PhD from the University of Pittsburgh in 2019.