Microwavephysics and Atmospheric Physics
Biomedizinische Photonik
Ultrafast Science and Technology
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Last update: 07.05.2018
FS 2012: Seminare über Ultrafast Science and Technology
Thursday 11:15am
Vorträge, die innerhalb der nächsten Tage stattfinden, sind speziell markiert.
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Mittwoch, 08.02.2012

The brightest issues of 10 years of seeding soft X-ray lasers

Zeit: 14:15 Uhr
Hörsaal: B116
Philippe Zeitoun
ENSTA-Paris Tech
Palaiseau cedex, France

Since the very first experiment on soft X-ray laser in the early 70’s, these lasers attracted a lot of interests for applications. The short wavelength opens up the possibility of getting new insight on matter by performing high-resolution images. However, contrary to most lasers, and despite many attempts, soft X-ray lasers were not demonstrating coherent beam for very long time. Also, at small spatial-scale matter tends to evolve very quickly requiring most often to use sub-picosecond flash of X-rays for catching a frozen picture. However, for decades, soft X-ray laser were blocked to pulse duration above several picoseconds. Since 2001, we are working both theoretically and experimentally in order to achieve the next generation of soft X-ray lasers using a laser-created plasma as amplifier. Our goal is to generate fully coherent, femtosecond soft X-ray lasers able to drive the most exciting and complex applications. From our first concept, to the first experiment and the last numerical studies, we discover that seeding soft X-ray lasers opens an outstanding sight inside atomic and plasma physics. Finally, we will expose a detailed design of a possible second generation soft X-ray laser able to produce the most intense beam worldwide, about 10,000 times more intense than best previous soft X-ray lasers.

Mittwoch, 22.02.2012

Electron acceleration through spatiotemporal pulse shaping (Promotionsvortrag)

Zeit: 10:00 Uhr
Hörsaal: B6
Reto Bloch
Institute of Applied Physics
University of Bern

Donnerstag, 01.03.2012

What are leap seconds? The atomic time and its relation to astronomical time scales

Zeit: 10:15 Uhr
Hörsaal: B116
Prof. André Stefanov
Quantum Optics Lab
Institute of Applied Physics
University of Bern

After a short history of the astronomical time scales used through the Ages, we will describe the actual realisation of the Coordinated Universal Time UTC, computed from an ensemble of atomic clocks. UTC is a post-processed paper time scale not accessible to everyone; we will show how the actual dissemination of UTC is performed by national institutes.

Leap seconds are additional seconds introduced in UTC to cope with the irregularities of the earth rotation. We will present how the parameters of the earth rotation are measured and how they affect UTC. The suppression of the leap seconds has been proposed and is actually discussed at the International Telecommunication Union. We will discuss the future of UTC depending on the decision which will be taken in 2015.

Mittwoch, 07.03.2012

Nonlinear Optical Effects in Hydrogenated Amorphous Silicon Wire Waveguides

Zeit: 10:15 Uhr
Hörsaal: B78
Edoardo Baldini
Faculty of Engineering
University of Pavia

Hydrogenated amorphous silicon (a-Si:H) is increasing its role as a promising material for the CMOS-compatible fabrication of optical waveguides in silicon photonics, as it allows more efficient nonlinear interactions than crystalline silicon. We want to investigate the ultrafast optical nonlinear response of a-Si:H wire waveguides using heterodyne pump-probe measurements, evaluating the cross-absorption and the cross-phase modulation and calculating the two-photon absorption figure of merit of the waveguides. Furthermore, we aim at describing the material degradation that can be observed after prolonged exposition of the waveguides to high-power laser radiation.

Donnerstag, 15.03.2012

joint IAP and DCB seminar on Physical Chemistry

From Computational Photobiology to the Development of Biomimetic Molecular Devices

Zeit: 11:15 Uhr
Hörsaal: B116
Prof. Massimo Olivucci
Laboratory for Computational Photochemistry & Photobiology
Bowling Green State University, OH, USA

During the last few years QM/MM computations based on the CASPT2//CASSCF approach have been employed to investigate spectroscopic and photochemical properties of light-sensitive proteins. In this lecture we will show how the same technology could be used to design light-driven molecular devices. In our lab we are exploring the possibility of designing and synthesizing molecules that could mimic the photoisomerization of the visual pigment Rhodopsin and, in particular its low-temperature photochromism [1]. When embedded in the opsin cavity the Rhodopsin chromophore displays an ultrafast and stereoselective photoisomerization with high quantum yield. In order to design a chromophore displaying a similar efficiency in common solvents we have been looking at diverse alkylated Schiff bases featuring a single isomerizable double bond. In this lecture we show that the indanylidene-pyrroline (NAIP) framework [2-4] provides a computationally and synthetically viable prototype for the development of systems that reproduce the excited state electronic structure and photoisomerization dynamics of Rhodopsin in methanol. We will also show that, on the basis of these studies we have been able to achieve systems that, in perspective, can be used as mechanical or electrostatic switches capable of inverting, reversibly, a ca. 15 D dipole moment upon double bond photoisomerization [5]. [1] Shapiro I., Ryazantsev M. N., Frutos L.-M., Ferré N., Lindh R. & Olivucci M. (2011) J Am Chem Soc 133:3354-3364. [2] Lumento F., Zanirato, V., Fusi, S., Busi, E., Latterini, L., Elisei, F., Sinicropi, A., Andruniów, T., Ferré, N., Basosi, R. & Olivucci, M. (2007) Angew Chem Int Ed Engl 46:414-420. [3] Sinicropi A., Martin, E., Ryasantsev, M., Helbing, J., Briand, J., Sharma, D., Léonard, J., Haacke, S., Cannizzo, A., Chergui, M., Zanirato, V., Fusi, S., Santoro, F., Basosi, R., Ferré, N. & Olivucci, M. (2008) Proc. Nat. Acad. Sci. USA 105:17642-17647. [4] Briand J., Bräm, O., Réhault, J., Léonard, J., Cannizzo, A., Chergui, M., Zanirato, V., Olivucci, M., Helbing, J. & Haacke, S. (2010) Phys Chem Chem Phys 12:3178 - 3187. [5] Melloni A., Rossi Paccani, R., Donati, D., Zanirato, V., Sinicropi, A., Parisi, M. L., Martin, E., Ryazantsev, M., Ding, W. J., Frutos, L. M., Basosi, R., Fusi, S., Latterini, L., Ferré, N. & Olivucci, M. (2010) J Am Chem Soc 132:9310-9319.

Donnerstag, 29.03.2012

Entangled photon sources based on spontaneous down conversion
(Masterarbeit Stefan Lerch)

Cavity enhanced coincidence detection of entangled photons
(Masterarbeit Markus Roesch)

Zeit: 10:15 Uhr
Hörsaal: B116
Stefan Lerch
Markus Rösch
Institute of Applied Physics
University of Bern

Donnerstag, 26.04.2012

Multi-stage ytterbium fiber-amplifier for weak picosecond laser pulses generated by a gain-switched laser-diode

Zeit: 10:15 Uhr
Hörsaal: B116
Dr. Manuel Ryser
Institute of Applied Physics
University of Bern

In the frame of a CTI project we have developed a five stage fiber-amplifier that is seeded by a gain-switched laser diode. The system delivers laser pulses of 11 picosecond pulse width (FWHM), with a peak power of >0.6MW and at a repetition rate of 1MHz. In this project was followed an interesting approach for the generation of energetic picosecond pulses: a gain-switched laser diode was combined with a multi-stage fiber amplifier. Gain-switching of laser diodes allows electronic triggering of the laser pulses that can be a very attractive feature for manifold applications such as for example material processing or nonlinear wave-mixing. Drawback of gain-switched laser diodes is the weak output pulse energy in the order of few 100fJ. However, fiber amplifiers allow the low-noise amplification of weak signals and are thus ideally suited to amplify the weak pulse trains from the gain-switched laser diodes. Our fiber-amplifier amplifies the input signal from the gain-switched laser-diode by 72dB. The core diameters of the fibers were increased for the successive stages from 4µm at the first stage to 70µm at the final amplification stage in order to minimize undesired non-linear effects or prevent from damage of the fibers due to the high peak powers. For the final amplification-stages was used a recently developed special fiber that only guides few modes, i.e. exhibits good beam quality, in spite of its large fiber core diameter of 70µm. In this talk details of the developed fiber laser system will be discussed. The low-noise Ytterbium fiber based amplification of the weak laser pulses generated by the gain-switched laser diode will be presented. Furthermore the fundamental physical limitations for ultra-short pulse amplification when reaching peak powers i.e. nonlinearities and fiber damage thresholds and ways to push these limits will be shown.

Donnerstag, 03.05.2012


joint IAP and DCB seminar on Physical Chemistry

Molecular monolayers on well defined surfaces: structure, bonding and dynamics

Zeit: 11:15 Uhr
Hörsaal: Chemie S481
Prof. Dr. Jürg Osterwalder
Universität Zürich

Donnerstag, 10.05.2012

A novel device for characterizing the index profile of optical fibers
(Masterarbeit Jonas Scheuner)

Cloaking at THz Frequencies
(Masterarbeit Yannik Waeber)

Zeit: 10:15 Uhr
Hörsaal: B116
Jonas Scheuner
Yannik Waeber
Institute of Applied Physics
University of Bern

Donnerstag, 31.05.2012

joint IAP and DCB seminar on Physical Chemistry

Rare-Earth Metal Cluster Complexes with Endohedral Atoms

Zeit: 11:15 Uhr
Hörsaal: Chemie S481
Prof. Dr. Gerd Meyer
Institut für Anorganische Chemie
Universität zu Köln

Donnerstag, 21.06.2012

Time & frequency activities at CSEM : from atomic clocks to stabilized lasers

Zeit: 10:15 Uhr
Hörsaal: B116
Steve Lecomte, PhD, Section Head, Time & Frequency Systems Division, CSEM Centre Suisse d'Electronique et de Microtechnique SA, Neuchâtel

Modern technologies and recent scientific breakthroughs have allow for massive improvement of devices like atomic clocks in the microwave and optical domains. Levels of frequency stabilities or size, power consumptions and costs are the focus of several activities at CSEM. The description of these activities as well as the on-going laser sources development and LIDAR projects will be presented.

Freitag, 06.07.2012

Light Sheet and Projection Tomography Techniques for in-vivo time-lapse imaging

Zeit: 10:15 Uhr
Hörsaal: A97
Prof. Jorge Ripoll Lorenzo, Physics Department, University of Fribourg

Light sheet techniques have gained considerable interest in microscopy, and have become one of the most useful approaches for high resolution imaging of large samples. In this talk I will present two approaches which use different illumination schemes, namely Selective Plan Illumination Microscopy and Optical Projection Tomography and showcase how each technique has its own advantages. The use of them combined will also be discussed, all based on the presence or absence of scattering.

Donnerstag, 02.08.2012

Präsentation der Bachelorarbeiten

Raman Spectroscopy (Sabine Joos)
Raman Microscopy (Gregory Gäumann)
Measuring Photon Statistics (Benjamin Gerber)

Zeit: 10:15 Uhr
Hörsaal: B116
Sabine Joos
Gregory Gäumann
Benjamin Gerber
Institute of Applied Physics
University of Bern