Microwavephysics and Atmospheric Physics
Biomedizinische Photonik
Ultrafast Science and Technology
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FS 2012  ·  HS 2011
Last update: 07.05.2018
FS 2015: Seminare über Ultrafast Science and Technology
Thursday 11:15am
Vorträge, die innerhalb der nächsten Tage stattfinden, sind speziell markiert.
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Donnerstag, 19.02.2015

Scientific workshop marking the retirement
of Prof. Dr. Jürg Balmer

Zeit: 15:15 Uhr
Hörsaal: B5
Prof. Dr. Peter Mulser
Institute of Applied Physics
Darmstadt University of Technology

Dr. Ernst Fill
Max Planck Institute of Quantum Optics
Attosecond Physics

see special announcement

Donnerstag, 26.02.2015

Optical and structural properties of Carbon nanodots and Metal-Organic Frameworks

Zeit: 11:15 Uhr
Hörsaal: B116
Dr. Fabrizio Messina
Laboratory of Advanced Materials Physics (LAMP)
Dipartimento di Fisica e Chimica
Università degli Studi di Palermo (Italy)

This seminar will focus on two separate scientific subjects we recently began investigating at the Laboratory of Advanced Materials Physics (LAMP).
1: Carbon nanodots (CDs) are a novel and rapidly emerging family of carbon-based nanomaterials. They are tiny (< 10 nm) and optically-active carbonaceous nanoparticles, which combine the capability of yielding intense fluorescence with water solubility, bio-compatibility and ease of synthesis. In our labs, we synthesize nitrogen-doped CDs and study them via a combination of optical and non-optical techniques. Our experiments eventually aim at elucidating the optical properties of these frontier nanomaterials, poorly understood so far.
2: Metal Organic Frameworks (MOFs) are porous crystalline materials built from a network of metal ions coordinated by organic ligands. Their large porosities, due to the presence of voids in the three-dimensional structure, combined with an extraordinary compositional variety, are extremely promising for a wide panel of applications such as storage and separation of gases, sensing, catalysis and drug-delivery. Our undergoing studies on MOFs mostly aim to learn how their structures are influenced by the adsorption of small molecules, and to investigate their stability, typically hindered by substantial aging processes occurring even in standard ambient conditions.

Donnerstag, 19.03.2015

Electron transport theories from the quantum to the ultra high field regimes

Zeit: 11:15 Uhr
Hörsaal: B116
Dr. Antonino La Magna
Istituto per la Microelettronica e Microsistemi
Catania, Italy

We review the formalism and the associated computational methods applied to the theoretical investigations of electronic transport in different regimes: From the quantum coherent to the semi-classical regimes, from the low to the high field regimes. The various conditions are characterized by device feature size, electrons energy distribution and transient response. Independently of the level and accuracy of the theory two necessary requirements are: a) the adequate description of the electronic structure of the studied systems and b) the self-consistent coupling with a Poisson solver for the evaluation of the electric field due to the external bias. The calculations of quantum transport rely on non-equilibrium Green's function formalism, where the estimate of the electronic structure is an inner part of the computation; whilst semi-classical schemes derived from the Boltzmann equation represent reliable approaches when quantum effects can be neglected. Particular examples of applications will be discussed for the case graphene based device (quantum transport) and the electron kinetics in semiconductors device under THz excitation at high electric field strength (semi-classical quasi-ballistic transport). In the first case, by varying both the width and the length of two-terminal devices from the nano- to the micro-scale, we discuss localization, pseudo-gap formation, transport length scales and conductance characteristics for variable defect/impurity concentrations. Ensemble Monte Carlo method can accurately simulate the semiconductor device features for transient electric field with strengths up to several hundred of kV/cm and device with feature length scale significantly larger than 10nm. Among the different scattering mechanisms carrier generation has to be consistently included in the computational model. Moreover, matter migration due to the hot electrons effects should be evaluated in order to understand observed permanent modifications of the device materials in operation conditions.

Donnerstag, 26.03.2015

Bloch surface waves, a 2D platform for planar optical integration

Zeit: 11:15 Uhr
Hörsaal: B116
Dr. Hans Peter Herzig
Optics & Photonics Technology Laboratory (OPT)
Swiss Federal Institute of Technology in Lausanne (EPFL)

A novel platform suitable for fundamental investigations of light propagation through micro- and nano-structures will be discussed. This platform is based on a dielectric multilayer that sustains Bloch surface waves (BSWs). BSWs are electromagnetic surface waves excited at the interface between a truncated periodic dielectric multilayer and a surrounding media. The modification of the top surface to customize a complete 2D micro-system can be produced using e-beam writing, optical lithography or other patterning techniques. The results obtained confirm the possibility of developing a robust multilayer platform that would pave the way for integration of photonic components in photonic chips using standard wafer-scale production.

Donnerstag, 02.04.2015

Temporal Diagnostics Measurements with the Pulse Arrival and Length Monitor (PALM) at SACLA

Zeit: 11:15 Uhr
Hörsaal: B116
Dr. Pavle Juranic
Paul Scherrer Institut PSI

Free Electron Lasers’ advantages over synchrotrons and other light sources lie in their shorter pulse lengths, higher intensities, and the possibility of performing pump-probe experiments with better time resolutions that what has been done thus far. The accurate, non-destructive measurement of FEL pulse length and arrival time relative to an experimental laser is, therefore, necessary for operators and users alike. The FEL operators can get a better understanding of their machine and the optics of an FEL by looking the pulse length changes of the photons coming to the user stations, and the users can use the arrival time and pulse length information to better understand their data. PSI has created the pulse arrival and length monitor (PALM) based on the THz-streak camera concept for measurement at x-ray FELs, meant to be used at the upcoming SwissFEL facility. The first results from the experimental beamtime at SACLA will be presented, showcasing the accuracy and reliability of the device. The prototype conducted the first THz streaking experiment with hard x-ray beams, and has not reached the limits of its accuracy. Further upgrades and possible developments will also be presented and discussed.

Donnerstag, 30.04.2015

Fundamentals and Applications of Plasma Filaments

Zeit: 11:15 Uhr
Hörsaal: B116
Prof. Ludger Wöste
Freie Universität Berlin, Institut für Experimentalphysik
Berlin, Germany

When sufficiently powered femtosecond laser pulses are launched into the atmosphere, white light emitting plasma filaments or even bundles of those are generated along the beam. Under well chosen pulse conditions these bundles may extend even over kilometre lengths. Their formation is based on a fascinating interplay of non-linear optical processes like Kerr lensing, plasma defocusing and self phase modulation. Filaments exhibit along their trajectory extraordinary properties, from which fascinating applications emerge. They emit, for example, directional white light in a wide spectral range from the IR to the UV, which can efficiently (> 60%) be extracted to produce ultra-short pulses (< 5fs). Further they allow the remote and simultaneous analysis of a rich variety of gaseous atmospheric constituents (fs- LIDAR), and when they hit solid or liquid targets, they emit intensive characteristic plasma light, which allows the remote identification of soil, vegetation, waters, etc. (F-LIBS). Until energy levels of 5mJ single filaments are formed. Their diameter is about 100 ? and their length reaches up to 100 metres. So at sufficient repetition rates (> 100 kHz) they cut materials or tissue at meters distance, without focussing the beam and without melting or burning the material.
Most interesting properties result from the plasma character of such filament bundles in air. Amazingly they can even be heard by ear, which provides a good and simple plasma monitor. More important, however, is the phenomenon, that the air along filament bundles becomes electrically conductive. The effect allows not only to guide and control electric discharges and currents, it provides a realistic chance to control lightings. With the advent of non-metallic airplanes this aspect has become most important for air traffic safety, namely for situations, when airplanes are obliged to land across thunderclouds. We have successfully demonstrated an influence of fs-laser induced filaments on a lightning. We are, however, still far off from reliably controlling them. So, in the future we wish to explore all critical parameters and develop concepts, how the requirements be met.
Another still fully unexplored, but quite relevant effect resulting from the plasma character of filaments is the formation of fog traces and droplets along their path in humid air. The basic effect is quite similar to the formation of charge traces in a Wilson-type fog chamber; but there are also striking differences: As our recent laboratory and field measurements clearly showed, laser-induced water condensation and droplet formation was not only observed in super saturated air but even when the air humidity was the below its saturation threshold. The effect is very promising and can well become a new and important tool in atmospheric research, namely the better understanding and possibly even local control of cloud formation. First, however, the effect must fully be characterized and understood.
The work was performed in the frame of the French-Swiss-German Teramobile project : together with J.P.Wolf, J.Kasparian, A. Mysyrowicz and R. Sauerbrey www.teramobile.org

Donnerstag, 07.05.2015

Development and application of a Raman spectrometer (Master's Thesis)

Zeit: 11:15 Uhr
Hörsaal: B116
Mehmet Oezdemir
Institute of Applied Physics
University of Bern

The first part of this thesis covers Raman spectroscopy in general and the specifications of the 532nm Raman setup in the IAP. The second part is about the measurement and analysis of several Raman spectra. It was used to qualitatively distinguish several chemicals and quantitatively the Ethanol content of various liquors. The spectrometer is able to resolve 5 cm^{-1}. Ethanol content of commercial liquors was measured with a precision of ~1% and an accuracy of ~0.5% depending on the sample.

Donnerstag, 14.05.2015

public holiday (Ascension Day)

Zeit: 11:15 Uhr
Hörsaal: B116

Donnerstag, 21.05.2015

Exciton-polariton Bose-Einstein condensation with a polymer at room temperature

Zeit: 11:15 Uhr
Hörsaal: B116
Dr. Thilo Stöferle
IBM Research GmbH
Zurich Research Laboratory

Integrated photonics is key for future data communication systems. A brief overview of the activities at IBM Research – Zurich will be given, with focus on our Quantum Photonics section, which investigates new microcavity structures and materials for enhanced light-matter interaction. In our experiments, we create exciton-polariton quasiparticles by exciting optically a microcavity filled with a ladder-type conjugated polymer in the strong coupling regime. At room temperature thermalization of these quasi-particles occurs while it is suppressed at low temperature because of a relaxation bottleneck. Above a certain excitation threshold with incoherent off-resonant picosecond laser pulses, we observe the emergence of non-equilibrium Bose-Einstein condensation in the lower polariton branch. This is evidenced by several distinct features such as a blue-shifted emission peak at zero in-plane momentum, accompanied by a nonlinear increase in the emission intensity and a sudden drop of the linewidth. Furthermore, the emission becomes polarized and the emission dynamics is drastically shortened. Spatially-resolved measurements with a Michelson interferometer show a macroscopic phase relation over almost the whole spot, and the fringe pattern exhibits non-flat phase fronts and fork-like dislocations, indicating a large number of vortices and excitations. Our approach demonstrates a radically simplified route to Bose-Einstein condensation physics at ambient conditions with easy-to-process non-crystalline materials.

Donnerstag, 28.05.2015

Dispersion measurements of fibres

Zeit: 11:15 Uhr
Hörsaal: B116
Jos Kohn
Université de Fribourg and Institute of Applied Physics
University of Bern

The dispersion properties of a fibre are important for studying the signal transmission through fibres. I will present a method for chromatic dispersion measurements using a white light Mach Zehnder interferometer. Furthermore I propose a modified reference arm by superposing beams of different optical path lengths. This modification simplifies the dispersion measurement of high dispersion Fibre Bragg gratings. In addition I will present an outlook for a measurement method for determining the chromatic dispersion of short few mode fibres. The technique relies on ultrafast coincidence detection based on the up-conversion of energy-time entangled photons.

Donnerstag, 30.07.2015

In-flight Density profiles and Non-uniformities in ICF Implosions

Zeit: 11:15 Uhr
Hörsaal: B116
Dr. Riccardo Tommasini
Lawrence Livermore National Laboratory
Livermore, CA (USA)

no abstract