Photoemission electron microscopy for nanoscale imaging and attosecond control of light-matter interaction at metal surfaces

Electron dynamics at solid surfaces unfold on the nanometer length and attosecond timescale when driven by electromagnetic fields at optical frequencies, enabling vast scientific and technological applications in the field of nano-optics and nanoplasmonics. Direct imaging of the electrons upon interaction with light is a highly desirable tool for understanding and control of the dynamics, which requires ultrahigh spatiotemporal resolution. This thesis explores the combination of photoemission electron microscopy (PEEM) with few-cycle femtosecond laser pulses and attosecond extreme ultraviolet (XUV) pulses for studying ultrafast electron dynamics from metallic surfaces and nanosystems. The work involves development and implementation of new experimental tools including detection, data acquisition and analysis techniques for PEEM measurements. The first approach is using a combination of PEEM with attosecond streaking spectroscopy (atto-PEEM) for direct, non-invasive probing of nanoplasmonic fields from supported nanostructures. As a first step towards the implementation of the atto-PEEM concept, PEEM imaging on lithographically fabricated gold structures employing 93 eV attosecond XUV pulses from a 1 kHz high-harmonic generation (HHG) source is performed. The spatial resolution is limited to ~200 nm due to space charge effects when working with such a low-repetition-rate HHG source and chromatic aberrations caused by the large energy bandwidth of XUV-generated photoelectrons. Nevertheless, we show that microspectroscopic imaging of core-level and valence band electrons is achievable using our energy-resolved PEEM despite the aforementioned issues. Most importantly, we find that the fast photoelectrons from the valence band, which carry the attosecond temporal structure of the plasmonic field, are not affected by space charge effects. The currently developed megahertz-repetition-rate attosecond XUV sources are therefore expected to enable the experimental realization of nanoplasmonic streaking with ultrahigh spatiotemporal resolution in the near future. Second, PEEM is coupled with a single-shot stereographic above-threshold ionization phase meter, which allows carrier-envelope phase (CEP) tagging for studying attosecond control of photoemission. First experiments performed on gold nanospheres on a gold plane and on a random rough gold surface using few-cycle near-infrared pulses show a CEP artefact with a modulation period of π. The artefact is found to be caused by a laser intensity dependence of both the photoelectron spectra and the CEP measurement. Intensity tagging is therefore added to the current CEP tagging technique to correct this intensity-dependent artefact. As a result, a very weak CEP modulation (~1% amplitude) of the photoemission yield from a bulk tungsten surface with a 2π modulation period (as expected from solids) is successfully detected in the above-threshold photoemission regime after applying appropriate corrections based on the intensity tagging. Entering the tunneling regime, the CEP modulation increases to ~7% despite the presence of space charge effects due to high laser peak intensity. We also apply this technique to investigate the CEP dependence on gold nanotriangles and find no apparent CEP modulation within an accuracy of ~0.6% as given by our experimental conditions, which constitutes an upper limit for a possible CEP modulation from this nanostructure.Elektronendynamik an Festkörperoberflächen, die von elektromagnetischen Feldern mit optischen Frequenzen getrieben wird, findet auf einer Längen- und Zeitskala im Bereich von Nanometern bzw. Attosekunden statt und ermöglicht eine Vielzahl wissenschaftlicher und technischer Anwendungen auf dem Gebiet der Nanooptik und Nanoplasmonik. Die direkte Visualisierung der Elektronen in Folge ihrer Wechselwirkung mit Licht, was eine ultrahohe räumlich-zeitliche Auflösung erfordert, ist ein sehr nützliches Instrument zum Verständnis dieser Dynamik und ihrer Kontrolle. In dieser Dissertation wird eine Kombination aus Photoemissionselektronenmikroskopie (PEEM) mit Femtosekundenlaserpulsen von wenigen Zyklen Dauer sowie extrem ultravioletten (XUV) Attosekundenpulsen erforscht, um ultraschnelle Elektronendynamik an Metalloberflächen und in Nanosystemen zu untersuchen. Diese Arbeit beinhaltet die Entwicklung und Implementierung neuer Messinstrumente und Methoden für PEEM-Experimente, insbesondere Detektion, Datenerfassung und Datenanalyse. Der erste Ansatz für eine direkte, nichtinvasive Untersuchung nanoplasmonischer Felder an ortsfesten Nanostrukturen ist eine Kombination von PEEM mit Attosekunden-Streaking (Atto-PEEM). Als eine Voraussetzung für die Implementierung des Atto-PEEM-Konzepts wird eine PEEM-Abbildung von lithographisch hergestellten Goldstrukturen mittels 93 eV XUV Attosekundenpulsen aus einer 1 kHz Quelle für die Erzeugung hoher Harmonischer realisiert. Wegen Raumladungseffekten, die durch die niedrige Repetitionsrate der hohen Harmonischen zustande kommen, sowie chromatischer Aberrationen aufgrund der hohen Energiebandbreite der durch die XUV-Strahlung erzeugten Photoelektronen, ist die räumliche Auflösung auf ~200 nm begrenzt. Dennoch wird gezeigt, dass trotz dieser Schwierigkeiten eine mikrospektroskopische Abbildung von inneren Elektronen und Valenzelektronen mittels unserer energieaufgelöster PEEM möglich ist. Unsere wichtigste Erkenntnis ist, dass die schnellen Photoelektronen aus dem Valenzband, die die zeitliche Struktur der plasmonischen Felder auf der Attosekundenskala abtasten, nicht durch Raumladungseffekte beeinträchtigt werden. Die sich derzeit in Entwicklung befindenden Quellen für Attosekunden-XUV-Pulse mit Megahertz Repetitionsraten sind daher vielversprechend für die experimentelle Realisierung von nanoplasmonischem Streaking mit ultrahoher räumlicher und zeitlicher Auflösung in naher Zukunft. Zweitens wird PEEM mit einem stereographischen, auf Above-Threshold-Ionisation basierenden Einzelschuss-Phasenmessgerät verbunden, was eine Zuordnung (Tagging) der Träger-Einhüllenden-Phase (carrier-envelope phase, CEP) erlaubt und dadurch ermöglicht, die Kontrolle der Photoemission auf der Attosekundenskala zu erforschen. Erste Experimente an Goldnanosphären auf einer Goldebene sowie an einer rauen Goldoberfläche mit wenige Zyklen kurzen Laserpulsen im Nah-Infraroten weisen ein CEP-Artefakt mit einer Modulationsperiode von π auf. Es wird gezeigt, dass dieses Artefakt durch eine Abhängigkeit sowohl der Photoelektronenspektra als auch der CEP-Messung von der Laserintensität hervorgerufen wird. Die bisherige CEP-Tagging-Technik wird deshalb um Intensitäts-Tagging erweitert, um dieses intensitätsabhängige Artefakt zu korrigieren. Als Resultat wird nach angemessenen Korrekturen basierend auf dem Intensitäts-Tagging eine schwache CEP-Modulation (~1% Amplitude) der Photoemissionsergiebigkeit von einer unstrukturierten Wolframoberfläche mit einer Modulationsperiode von 2π (wie bei Festkörpern erwartet) im Above-Threshold-Photoemissionsregime erfolgreich nachgewiesen. Im Tunnelregime wächst die CEP-Modulation auf ~7% trotz aufkommender Raumladungseffekte aufgrund der starken Spitzenintensität der Laserpulse. Es werden ebenfalls Goldnanodreiecke mit dieser Technik untersucht, jedoch kann keine CEP-Modulation innerhalb der experimentellen Genauigkeit von ~0.6% gefunden werden. Dies stellt eine Obergrenze für eine mögliche CEP-Modulation an dieser Nanostruktur dar

Fiber Bragg Grating Based Sensors and Systems

This book is a collection of papers that originated as a Special Issue, focused on some recent advances related to fiber Bragg grating-based sensors and systems. Conventionally, this book can be divided into three parts: intelligent systems, new types of sensors, and original interrogators. The intelligent systems presented include evaluation of strain transition properties between cast-in FBGs and cast aluminum during uniaxial straining, multi-point strain measurements on a containment vessel, damage detection methods based on long-gauge FBG for highway bridges, evaluation of a coupled sequential approach for rotorcraft landing simulation, wearable hand modules and real-time tracking algorithms for measuring finger joint angles of different hand sizes, and glaze icing detection of 110 kV composite insulators. New types of sensors are reflected in multi-addressed fiber Bragg structures for microwave–photonic sensor systems, its applications in load-sensing wheel hub bearings, and more complex influence in problems of generation of vortex optical beams based on chiral fiber-optic periodic structures. Original interrogators include research in optical designs with curved detectors for FBG interrogation monitors; demonstration of a filterless, multi-point, and temperature-independent FBG dynamical demodulator using pulse-width modulation; and dual wavelength differential detection of FBG sensors with a pulsed DFB laser

Air Force Institute of Technology Research Report 2009

This report summarizes the research activities of the Air Force Institute of Technology’s Graduate School of Engineering and Management. It describes research interests and faculty expertise; lists student theses/dissertations; identifies research sponsors and contributions; and outlines the procedures for contacting the school. Included in the report are: faculty publications, conference presentations, consultations, and funded research projects. Research was conducted in the areas of Aeronautical and Astronautical Engineering, Electrical Engineering and Electro-Optics, Computer Engineering and Computer Science, Systems and Engineering Management, Operational Sciences, Mathematics, Statistics and Engineering Physics

Optical Signal Processing For Data Compression In Ultrafast Measurement

Today the world is filled with continuous deluge of digital information which are ever increasing by every fraction of second. Real-time analog information such as images, RF signals needs to be sampled and quantized to represent in digital domain with help of measurement systems for information analysis, further post processing and storage. Photonics offers various advantages in terms of high bandwidth, security, immunity to electromagnetic interference, reduction in frequency dependant loss as compared to conventional electronic measurement systems. However the large bandwidth data needs to be acquired as per Nyquist principle requiring high bandwidth electronic sampler and digitizer. To address this problem, Photonic Time Stretch has been introduced to reduce the need for high speed electronic measurement equipment by significantly slowing down the speed of sampling signal. However, this generates massive data volume. Photonics-assisted methods such as Anamorphic Stretch Transform, Compressed Sensing and Fourier spectrum acquisition sensing have been addressed to achieve data compression while sampling the information. In this thesis, novel photonic implementations of each of these methods have been investigated through numerical and experimental demonstrations. The main contribution of this thesis include (1) Application of photonic implementation of compressed sensing for Optical Coherence Tomography, Fiber Bragg Grating enabled signal sensing and blind spectrum sensing applications (2) Photonic compressed sensing enabled ultra-fast imaging system (3) Fourier spectrum acquisition for RF spectrum sensing with all-optical approach (4) Adaptive non-uniform photonic time stretch methods using anamorphic stretch transform to reduce the the number of samples to be measured