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  4. Vahid Sandoghdar

Prof. Vahid Sandoghdar

  • Director
  • Head of Nano-Optics Division

The research of our group aims to advance experimental and theoretical mastery of light-matter interaction at the nanometer scale and to achieve the same degree of control and finesse that is known from the gas-phase quantum optics in the condensed phase. To do this, we combine concepts from quantum optics, laser spectroscopy, cryogenics, optical imaging, scanning probe technology and nanofluidics. In this endeavour, we have addressed a wide spectrum of scientific questions, ranging from quantum optics to biophysics. For more information, please consult our research website and our list of publications.

2015

Light microscopy: an ongoing contemporary revolution

Siegfried Weisenburger, Vahid Sandoghdar

Contemporary Physics 56 123-143 (2015) | Journal

The optical microscope is one of the oldest scientific instruments that is still used in forefront research. Ernst Abbe's nineteenth century formulation of the resolution limit in microscopy let generations of scientists believe that optical studies of individual molecules and resolving subwavelength structures were not feasible. The Nobel Prize in 2014 for super-resolution fluorescence microscopy marks a clear recognition that the old beliefs have to be revisited. In this article, we present a critical overview of various recent developments in optical microscopy. In addition to the popular super-resolution fluorescence methods, we discuss the prospects of various other techniques and imaging contrasts and consider some of the fundamental and practical challenges that lie ahead.

Spectroscopic detection of single Pr3+ ions on the H-3(4)-D-1(2) transition

Emanuel Eichhammer, Tobias Utikal, Stephan Goetzinger, Vahid Sandoghdar

New Journal of Physics 17 083018 (2015) | Journal

Rare earth ions in crystals exhibit narrow spectral features and hyperfine-split ground states with exceptionally long coherence times. These features make them ideal platforms for quantum information processing in the solid state. Recently, we reported on the first high-resolution spectroscopy of single Pr3+ ions in yttrium orthosilicate nanocrystals via the H-3(4)-P-3(0) transition at a wavelength of 488 nm. Here we show that individual praseodymium ions can also be detected on the more commonly studied H-3(4)-D-1(2) transition at 606 nm. In addition, we present the first measurements of the second-order autocorrelation function, fluorescence lifetime, and emission spectra of single ions in this system as well as their polarization dependencies on both transitions. Furthermore, we demonstrate that by a proper choice of the crystallite, one can obtain narrower spectral lines and, thus, resolve the hyperfine levels of the excited state. We expect our results to make single-ion spectroscopy accessible to a larger scientific community.

Enhancing the radiative emission rate of single molecules by a plasmonic nanoantenna weakly coupled with a dielectric substrate

X. W. Chen, K. G. Lee, H. Eghlidi, Stephan Götzinger, Vahid Sandoghdar

Optics Express 23 32986-32992 (2015) | Journal

Enhancing the spontaneous emission of single emitters has been an important subject in nano optics in the past decades. For this purpose, plasmonic nanoantennas have been proposed with enhancement factors typically larger than those achievable with optical cavities. However, the intrinsic ohmic losses of plasmonic structures also introduce an additional nonradiative decay channel, reducing the quantum yield. Here we report on experimental studies of a weakly coupled dielectric substrate and a plasmonic nanoantenna for enhancing the radiative decay rate of single terrylene molecules embedded in an ultrathin organic film. We systematically investigate how the refractive index of the dielectric substrate affects the lifetime and the quantum efficiency and show that the coupled structure could moderately enhance the radiative decay rate while maintaining a high quantum efficiency. (C)2015 Optical Society of America

Nano-Quantenoptik

Tobias Utikal, Emanuel Eichhammer, Benjamin Gmeiner, Andreas Maser, Daqing Wang, Pierre Türschmann, Hrishikesh Kelkar, Nir Rotenberg, Stephan Götzinger, et al.

MPG Jahrbuch 2015 (2015) | Journal

Nanoskopische Quantensysteme in einem Festkörper finden in der Quantenoptik zunehmend an Bedeutung. Deren Integrierbarkeit in photonische Nanostrukturen machen sie zu aussichtsreichen Kandidaten zur Realisierung von zukünftigen Quantennetzwerken. Als Grundbaustein konnte kürzlich die effiziente Kopplung von einzelnen Molekülen an photonische Wellenleiterstrukturen gezeigt werden. Mit neuartigen Mikroresonatoren ist es möglich, die optische Kopplung zwischen einzelnen Quantensystemen zu untersuchen. Unterdessen kommen sogar einzelne Ionen in einem Kristall in der Nano-Quantenoptik zum Einsatz.

When excitons and plasmons meet: Emerging function through synthesis and assembly

Jennifer A. Hollingsworth, Han Htoon, Andrei Piryatinski, Stephan Goetzinger, Vahid Sandoghdar

MRS Bulletin 40 768-776 (2015) | Journal

To meet the challenge of precise nanoscale arrangement of emitter and plasmonic nanoantenna, synthesis and assembly methods continue to evolve in accuracy and reproducibility. This article reviews some of the many strategies being developed for "soft" chemical approaches to precision integration and assembly. We also discuss investigations of the Purcell effect, emission directionality control, and near-unity collection efficiency of photons, emitter emitter coupling, and higher-order emission processes that have been most deeply explored using individual-emitter- (or several-emitter-) nanoantenna pairs fabricated using traditional lithographic methods or dynamically and controllably manipulated using scanning probe methods. Importantly, these results along with theoretical analyses inspire and motivate continued advancements in large-scale synthesis and assembly. We emphasize assembly approaches that have been used to create nanosemiconductor-nanometal hybrids and, in particular, those that have afforded specific plasmonic effects on excitonic properties. We also review direct-synthesis and chemical-linker strategies to creating discrete, though less spatially extended, semiconductor-metal interactions.

Sensing Nanoparticles with a Cantilever-Based Scannable Optical Cavity of Low Finesse and Sub-lambda(3) Volume

Hrishikesh Kelkar, Daqing Wang, Diego Martin-Cano, Bjoern Hoffmann, Silke Christiansen, Stephan Goetzinger, Vahid Sandoghdar

Physical Review Applied 4 054010 (2015) | Journal

We report on the realization of an open plane-concave Fabry-Perot resonator with a mode volume below lambda(3) at optical frequencies. We discuss some of the less-common features of this microcavity regime and show that the ultrasmall mode volume allows us to detect cavity resonance shifts induced by single nanoparticles even at quality factors as low as 100. Being based on low-reflectivity micromirrors fabricated on a silicon cantilever, our experimental arrangement provides broadband operation, tunability of the cavity resonance, and lateral scanning. These features are interesting for a range of applications including biochemical sensing, modification of photophysics, and optomechanical studies.

Fabrication and characterization of plasmonic nanocone antennas for strong spontaneous emission enhancement

Bjoern Hoffmann, Simon Vassant, Xue-Wen Chen, Stephan Goetzinger, Vahid Sandoghdar, Silke Christiansen

Nanotechnology 26 404001 (2015) | Journal

Plasmonic antennas are attractive nanostructures for a large variety of studies ranging from fundamental aspects of light-matter interactions at the nanoscale to industry-relevant applications such as ultrasensitive sensing, enhanced absorption in solar cells or solar fuel generation. A particularly interesting feature of these antennas is that they can enhance the fluorescence properties of emitters. Theoretical calculations have shown that nanocone antennas provide ideal results, but a high degree of manufacturing precision and control is needed to reach optimal performance. In this study, we report on the fabrication of nanocones with base diameters and heights in the range of 100 nm with variable aspect ratios using focused ion beam milling of sputtered nano-crystalline gold layers. The controlled fabrication process allows us to obtain cones with tailored plasmon resonances. The measured plasmon spectra show very good agreement with finite-difference time-domain calculations. Theoretical investigations predict that these nanocones can enhance the spontaneous emission rate of a quantum emitter by several hundred times while keeping its quantum efficiency above 60%.

Born on April 29, 1966 in Tehran, Iran. Bachelor of Science in Physics from the University of California in Davis (1987), Ph.D. in Physics (supervisors: E. A. Hinds and S. Haroche) from Yale University (1993), Postdoctoral Fellow at École Normale Supérieure (group of S. Haroche) in Paris. Head of the Nano-Optics group und habilitation in Physics at University of Konstanz (Chair of J. Mlynek). Professorship at Eidgenössischen Technischen Hochschule (ETH) Zurich (2001-2011). Recipient of an ERC Advanced Grant (2010). Alexander von Humboldt Professorship at Friedrich-Alexander-Universität Erlangen-Nürnberg and Director and Scientific Member at the Max Planck Institute for the Science of Light in Erlangen since 2011. Fellow of the Optical Society (OSA) and recepient of the 2023 Quantum Electronics and Optics Award for Fundamental Aspects from the European Physical Society. Founder of the Max-Planck-Zentrum für Physik und Medizin, a joint research center that aims to address questions in fundamental medical research with physical and mathematical methods.

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