Microwavephysics and Atmospheric Physics
Biomedizinische Photonik
Ultrafast Science and Technology
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Last update: 07.05.2018
HS 2013: Seminare über Ultrafast Science and Technology
Thursday 11:15am
Vorträge, die innerhalb der nächsten Tage stattfinden, sind speziell markiert.
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Donnerstag, 19.09.2013

Generation of high field enhancement of THz light using Nano-antennas

Zeit: 10:15 Uhr
Hörsaal: B116
Salvatore Bagiante
PSI Paul Scherrer Institut

THz meta-materials or rather fundament building blocks thereof can be useful, if modified slightly, in a completely different area of research, namely THz science. Recent experiments conducted by Seo and coworkers [1], using a gold film with a single nano-slit, showed that it is possible to significantly enhance the THz field strength inside the gap region. Starting from this investigation we designed and tested a range of nano-structure components. They were built to further enhance the THz field strengths and to allow previously impossible nonlinear THz experiments. In this talk the concept of a nano-antenna and its fabrication process will be introduced and discussed. Moreover, the field enhancement in arrays of nano-slits, split ring resonators, and other sub-wavelength antennas will be shown. 3D electromagnetic simulations as well as sophisticated near-field measurements will be also presented.

Donnerstag, 26.09.2013

A mechanical sensor to study movement at the nanoscale

Zeit: 10:15 Uhr
Hörsaal: B116
Giovanni Longo
Laboratory of the Physics of Living Matter LPMV

The importance of the characterization of movement in biological samples ranges from the fields of biology and microbiology to pharmaceuticals and drug development. For instance, the movement of living systems can deliver useful information regarding the metabolism of the specimen under investigation and can be used to define their response to external stimuli. In this presentation I will show how nanomechanical sensors can be used to characterize the nano-sized fluctuations of biologically-interesting specimens. I will discuss the metabolism-related movements of different bacterial species, of yeasts and fungi and of plant and mammalian cells when exposed to various external stimuli. For instance I will show how bacteria react to antibiotics and how nanomechanical sensors can be used as extremely fast tools (minutes, compared to hours or days) to characterize bacterial resistances. Furthermore I will discuss how this system can be applied to the study of conformational changes in proteins and protein complexes. These studies have defined how this new diagnostic tool can be used to characterize biological samples and how this information can be used to understand better their metabolic pathways. The speed and sensitivity of the technique will have a massive impact, with applications in general and molecular biology, microbiology, drug development and medicine. Its versatility allows also foreseeing its possible future use to identify and characterize life in hostile environments.

Montag, 30.09.2013

PhD defense: Shaping of Energy-Time Entangled Photons

Zeit: 10:15 Uhr
Hörsaal: B78
Christof Bernhard
Institute of Applied Physics
University of Bern

Donnerstag, 10.10.2013

Theory and Simulation of Laser Cutting of metals

Zeit: 10:15 Uhr
Hörsaal: B116
Dr. Michael Brügmann
Institute of Applied Physics
University of Bern

Theoretical aspects and calculations of the process of fusion laser cutting of metals will be presented. After a short introduction to the process and most important methods of laser cutting of metals we shall focus on the problem of laser cutting from the theoretical point of view.
The dynamics of the cutting front and the molten layer as well as its relation to cut quality affecting phenomena like ripple formation and adherent dross will be discussed. Specifically we investigated the dependence of relevant parameters, such as the maximum cutting speed, the shape of the cutting front, the absorptivity profiles and other relevant quantities on the wavelength, polarization and beam properties of the laser source. Special emphasis was placed on the comparison between results obtained for solid state lasers around 1 µm and CO2 lasers at 10 µm wavelength respectively. In general, we found good agreement between theoretical and experimental results and showed that the main differences between laser cutting with 1 µm and 10 µm beams arise from the different absorptivity profiles and absorbed intensities.

Donnerstag, 17.10.2013

7.36 nm Ni-like Sm Soft-x-ray Laser

Zeit: 10:15 Uhr
Hörsaal: B116
Fei Jia
Institute of Applied Physics
University of Bern

Compared with modern short wavelength sources, working in the wavelengths of sub-10 nm or less, the plasma soft-X-ray laser offers outstanding spectral resolution with high peak brilliance of several orders of magnitude greater than any other existing sources such as HHG, synchrotron radiation and FELs. The recent introduction of the grazing-incidence pumping (GRIP) and travelling wave excitation (TWE) schemes have greatly improved the efficiency of soft-X-ray lasers operating in the 10-20 nm regions.
In this talk, I will present the latest results which we attempt to move towards shorter wavelengths down to 7.36 nm by using Ni-like samarium (Sm) as the gain medium and pumped by the 10-TW Nd:glass CPA (chirped-pulse amplification) laser system. With a infrared pump pulse energy of 13 J in 1.5 ps pulse duration, a near-saturated soft-X-ray lasing on the 4d -> 4p, J = 0-1 line of Sm at the wavelength of 7.36 nm was achieved and delivers pulse energy of 3-4 µJ. Since the intrinsic character of ASE signal group velocity variation and the relatively short gain life-time, the temporal-spatial synchronization of ASE signal with respect to the TWE velocity becomes significant. Therefore, I will show a novel method to introduce a varied TWE velocity with a positive slope along the gain medium by modifying our grating compressor and focusing optics according to the results of numerical simulations.

Donnerstag, 24.10.2013

Toward experimental two-photon absorption with entangled photons

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

In 1930, Maria Goeppert-Mayer predicted for the first time two-photon absorption (TPA). With femtosecond lasers it became possible to measure TPA. About 70 years later, the cross-section for two-photon absorption with entangled photons was theoretically introduced. We will present in particular the linear dependence of the two-photon absorption rate on the light intensity and the possibility to gain spectroscopic information out of it. It has been shown that it is even possible to resolve virtual states which contribute to the TPA but whose energies exceed the sum of the entangled photon energies. This phenomena is accordingly termed “Entangled-Photon Virtual-State Spectroscopy”. The second part of the talk focus on the experimental setup which will allow to measure entangled TPA on different absorbers, for instance fluorescent molecules or atomic Rubidium. By means of Zemax and Lab2 simulations, I will illustrate the work going on in order to improve the present setup of the entangled photon source and shaper.

Dienstag, 29.10.2013

PhD defense: Steady State and Time-resolved Raman and Absorption Spectroscopies for Chemical Recognition and Molecular Dynamical Studies

Zeit: 09:15 Uhr
Hörsaal: B7
Nina Schönbächler
Institute of Applied Physics
Universtity of Bern

Donnerstag, 07.11.2013

Distortion-free enhancement of THz signals measured by electro-optic sampling

Zeit: 10:15 Uhr
Hörsaal: B116
Dr. Fabian Brunner
Institute of Applied Physics
University of Bern

A tutorial on the detection of THz pulses in cubic electro-optic crystals (known as electro-optic sampling) will be given. A method for the distortion-free enhancement of the THz signal will be explained in three different setup configurations derived from optically heterodyne detected optical Kerr effect spectroscopy. We could experimentally demonstrate enhancement factors larger than 10. It will be shown that electro-optic sampling can be interpreted as optical heterodyne detection under certain conditions. Furthermore, the investigation of a novel organic electro-optic crystal for efficient THz generation will be presented. Finally, ongoing work about the shift of the resonance frequency of split ring resonators at high THz electric field strengths will be discussed.

Donnerstag, 14.11.2013

Self-photopumped Ne-like and Ni-like X-ray laser

Zeit: 10:15 Uhr
Hörsaal: B116
Michael Siegrist
Institute of Applied Physics
University of Bern

The very successful collisional excitation scheme has been studied for decades and several pump techniques have been developed such as grazing-incidence pumping (GRIP), multipulse pumping and traveling wave excitation (TWE). The pumping mechanism is not necessarily limited to the collisional excitation scheme. A self-photopumped mechanism has already been proposed, but the requirement of high intensity has always been an issue. Since the CPA technique has been well developed, Terawatt infrared pump pulses are accessible on the lab scale. Applying those already matured pump technologies, one can achieve lasing on the „self-photopumped“ 3d -> 3p and the 4f -> 4d laser lines for Ne- and Ni-like ions, respectively. I will mainly focus on presenting results achieved on photopumped laser lines for materials in the Ne-like and the Ni-like ionization states.

Donnerstag, 21.11.2013

Time resolved Stark effect of proteins some attempts from the past, what is possible now?

Zeit: 10:15 Uhr
Hörsaal: B116
Dr. Frank van Mourik
Institute of Chemical Sciences and Engineering
Laboratory of Ultrafast Spectroscopy
EPFL Lausanne

Donnerstag, 28.11.2013

Heralded entanglement between distant atoms.
Towards a loophole free test of Bell's inequality ?

Zeit: 16:15 Uhr
Hörsaal: B116
Prof. Dr. Harald Weinfurter
Fakultät für Physik, Ludwig-Maximilians-Universität, München, Germany
and Max-Planck-Institut für Quantenoptik, Garching, Germany

We report on the generation and analysis of heralded entanglement between spins of two single 87Rb atoms trapped independently 20 meters apart. The data observed violate a Bell type entanglement without the detection loophole even for the large separation.

We discuss the progress towards an experiment to close both detection loophole and the locality loophole simultaneously.

Freitag, 29.11.2013

PhD defense: Shaped Energy-Time Entangled Two-Photon States for Quantum Information

Zeit: 10:15 Uhr
Hörsaal: B77
Bänz Bessire
Institute of Applied Physics
University of Bern

Donnerstag, 05.12.2013

Progress on rare earth doped optical fiber fabrication by Sol-Gel and granulates silica method

Zeit: 10:15 Uhr
Hörsaal: B116
Dereje Etissa
Institute of Applied Physics
University o Bern

In 1961, Elias Snitzer and colleagues constructed and operated the world's first fiber optical amplifier. The real breakthrough of fiber optic amplifiers was then achieved in 1987 by the invention of the erbium-doped fiber amplifier that allowed long-haul intercontinental fiber optic communication. Since then, the optical output power of fiber optic amplifiers and fiber laser has increased dramatically, enabled by the invention of specialty optical fibers with always larger cores. However the upper limit is still not reached.
The Optical Fibers and Fiber Lasers group also participates in the fabrication of innovative optical fibers and operates a fiber drawing tower. Our approach is based on the unique granulated silica method, offering great simplification of manufacturing optical fibers with a large variety of dopants, choice of index distributions, flexible fiber geometries and dopant concentrations. This is especially true if the solgel method is used to produce the doped granulated silica. In particular, the sol-gel method allows the inclusion of P2O5 and thus, in combination with Al2O3, higher dopant concentration of active rare earths such as Ytterbium is possible. The price one has to pay for these advantages over standard preform and fiber production techniques are the intrinsically higher OH content and the high scattering losses. However, both disadvantages are of low importance in applications where only short fiber lengths are involved, such as fiber lasers and amplifiers. In this talk the state of the art of our granulated silica method is presented as well as the last progresses in the production of rare earth doped optical fibers.

Donnerstag, 12.12.2013

High – performance LiF crystal and film quantum beam detectors for high-resolution imaging

Zeit: 10:15 Uhr
Hörsaal: B116
Prof. Anatoly Faenov
Joint institute for High Temperature
Russian Academy of Sciences
Moscow, Russia and
Quantum Beam Science Directorate
Japan Atomic Energy Agency, Japan

Main principles of operation and review of results, obtained by using recently proposed high-performance imaging detector, based on formation of color centers in LiF crystal and film will be presented. It will be discussed applications of such detectors for:
1) Submicron soft X-ray radiography of low-contrast objects, including nanofoils, membranes and biological structures. A spatial resolution of ~ 700 nm in the field of view of few square centimeters has been demonstrated in the imaging system consisted of a specially developed, very bright, debris-free femtosecond-laser-driven cluster-based plasma soft X-ray source and a submicron, high dynamic range LiF crystal detector. High performance absorption and propagation-based phase-contrast images of ultrathin foils with few nanometer variations of thickness and of micron size point defects presence have been obtained. The homogeneity of 100 nm Mo or Zr foils were measured with the accuracy ± 3%. Altogether, it has opened a new opportunity for novel ultrafast soft X-ray diagnostics and metrology of large size free standing or mesh supported nano-thickness foils or other nanostructures.

2) In situ sub-micron measurements of near-field and far-field properties of soft X-ray laser-driven transient-collision plasma and free electron laser beams. It has been shown that due to favorable combination of high spatial resolution, high dynamic range and wide field of view the LiF detectors allow measuring a highly detailed intensity distribution across the full size of the beams well as permit to evaluate spatial distribution of coherence and spectral properties of radiation across the beam. Newly applied, based on the diffraction imaging of periodical structures illuminated by investigated beam allowed to estimated accuracy of measurements in order of ~ 10-20%.

3) A single shot imaging of relativistic high order harmonic (HOH) beams. That is a new type of HOH, generated by an oscillating electron spikes formed in underdense gas jet plasma created by relativistically self-focusing laser pulses. The LiF film was used for near-field diffraction imaging of the HOH beam and investigation of its coherent properties. The focusability of the HOH beam was investigated using spherical Mo/Si mirror and LiF crystal. Using such technique the sizes and complexity of the HOH source structure have been measured with spatial resolution of ~ 200 nm.

4) High-performance neutron imaging. It was demonstrated that the LiF detectors have practically linear response on the thermal neutron fluence in the dynamic range of at least 103 and allow obtaining neutron radiographic images with spatial resolution of ~ 5 µm. The images are almost free from granular noise. Moreover, detailed evaluation using a standard sensitivity indicator for neutron radiography showed that two holes with less than 2% transmittance differences could be distinguished. Additionally, we recently demonstrated that the high resolution neutron imaging with LiF crystals could be useful for quantitative characterizations of neutron sources and electric devices, comprising of low-Z elements, for example, such as fuel cells. All of this gives new opportunity for microns scale spatial resolution imaging by neutrons in areas, where a high spatial resolution with a high image gradation resolution is needed.