Nanoantennas for visible and infrared radiation

Nanoantennas for visible and infrared radiation can strongly enhance the interaction of light with nanoscale matter by their ability to efficiently link propagating and spatially localized optical fields. This ability unlocks an enormous potential for applications ranging from nanoscale optical microscopy and spectroscopy over solar energy conversion, integrated optical nanocircuitry, opto-electronics and density-ofstates engineering to ultra-sensing as well as enhancement of optical nonlinearities. Here we review the current understanding of optical antennas based on the background of both well-developed radiowave antenna engineering and the emerging field of plasmonics. In particular, we address the plasmonic behavior that emerges due to the very high optical frequencies involved and the limitations in the choice of antenna materials and geometrical parameters imposed by nanofabrication. Finally, we give a brief account of the current status of the field and the major established and emerging lines of investigation in this vivid area of research.Comment: Review article with 76 pages, 21 figure

Advanced Focused Beam-Induced Processing for Nanoscale Synthesis and 2D Materials Device Architectures

Nanofabrication has come to prominence over recent years due to miniaturization of electronic devices as well as interesting physical phenomena that arise in material systems at the nanoscale. Particle beam induced processing enables additive as well as subtractive nanoprocessing techniques. Focused beam induced processing facilitates direct-write processing, thus making it a common technique for fabrication and synthesis on the nanoscale and is typically carried out with charged particles such as electrons or ion species, each of which offer distinct capabilities. This dissertation addresses several challenges which currently plague the focused beam-induced processing community and explores novel applications.Chapter I explores laser based purification strategies for electron beam induced deposition. This addresses the challenge of material purity, which currently limits broader application of the nanofabrication technique. Chapter II covers advanced helium ion beam induced processing using a Gas Field Ionization source. This chapter explores novel applications for the helium ion beam as well as the mitigation of helium-induced subsurface damage, which currently prevents ubiquitous adoption of the helium ion microscope as a nanofabrication tool. Chapter III studies defect introduction in 2D materials under helium ion irradiation, which proves to be an ideal nanoprocessing application for the helium ion beam

Atoms in intense ultrashort laser pulses and the absolute phase

Diese Arbeit beschäftigt sich mit der experimentellen Analyse atomarer Prozesse in intensiven ultrakurzen Laserpulsen. Der Schwerpunkt liegt hierbei bei den Zwillingseffekten der Erzeugung hoher Harmonischer (``high-order harmonic generation'', HHG) und der Ionisation über Zustände im Kontinuum (``above-threshold ionization'', ATI). Besonders letzterer Effekt wird detailliert in Verbindung mit der Wechselwirkung mit Laserpulsen von nur wenigen Zyklen Länge untersucht. Während es heutzutage Routine ist solche Pulse von weniger als 5 fs zu erzeugen, war die vollständige Kontrolle über das zugrundeliegende elektrische Feld bisher noch nicht möglich. Dies wurde in dieser Arbeit durch die erste eindeutige Messung der den Laserpuls charakterisierenden ``absoluten Phase'' erreicht. Die Genauigkeit und Zuverlässigkeit dieser Messung erweist sich als hinreichend, um eine neue Methode der aktiven Phasenstabilisierung einzuführen, welche voraussichtlich eine tragende Rolle in zukünftigen phasenstabilisierten Lasersystemen spielen wird. Die beschriebenen Experimente widmen sich zudem auch allgemeinen optischen Effekten, wie beispielsweise der Gouy'schen Phasenanomalie in einem fokussierten Strahl, welche hier erstmals im optischen Bereich und über den gesamten Fokusbereich gemessen wurde. Schliesslich wird gezeigt, wie ATI in Verbindung mit Wenig-Zyklen-Laserpulsen nicht nur als leistungsfähiges Werkzeug zur Phasendiagnostik genutzt werden kann, sondern auch einen neuen Zugang zur Untersuchung der Wechselwirkung von Atomen und Licht mit bis dato unerreichter Zeitauflösung bietet.The subject of this work is the experimental investigation of atomic processes under the influence of intense, ultrashort laser pulses. Emphasis is given to the twin effects of high-order harmonic generation (HHG) and above-threshold ionization (ATI). In particular, the latter is explored in detail here for the case of few-cycle laser pulses. While the generation of light pulses of duration below 5 fs is today routine, a complete control of the constituting electric-field waveform was so far not possible. This is here achieved with the first unambiguous measurement of the absolute phase of the laser pulses. The precision and reliability of the measurement permitted to establish a new approach for active phase stabilization, which will presumably play a major role in future research. The experiments described here address also general optical properties such as the Gouy phase anomaly showing up in a focused wave, being precisely measured for the first time. Finally, it is shown how ATI with few-cycle laser pulses can be regarded not only as a powerful tool for phase diagnostics, but also as a novel method for studying the interaction of atoms with light with unprecedented sub-fs time resolution