Kolloquien

Die Gastvorträge im Rahmen des MPQ-Kolloquiums finden von April bis Juli sowie von Oktober bis Januar jeweils dienstags um 14:30 Uhr statt. Verantaltungsort ist der Herbert-Walther-Hörsaal im Foyer des Max-Planck-Instituts für Quantenoptik.

Ansprechpartner für die wissenschaftliche Organisation:

Dr. Stephan Dürr und Dr. Thomas Udem

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"Casimir forces are macroscopic manifestations of QED and can be designed by altering the shape and material of the interacting bodies. In addition to experiments on attractive and repulsive forces that emphasize this dependence, I will discuss a number of exotic yet –to-be-observed effects such as the vacuum torque, vacuum radiation from oscillating cavities and related phenomena. Casimir forces offer both limits and exciting opportunities for the operation of future Nano-ElectroMechanical-Systems (NEMS)." [mehr]
"A new class of plasmonic interfaces is presented which greatly expands the capability of plasmonics for science and technology. I will discuss: polarization controlled tunable directional coupling of surface plasmons (SP); holographic metasurfaces that generate broadband radially polarized beams, holographic vortex detectors and the generation for the first time of straight propagating diffraction less SP beams (cosine-Gauss beams and bottle beams). These findings have potential applications in quantum information processing, chip interconnects and nanoparticle trapping." [mehr]
"Acceleration of particles at high gradient is an intense research topic. Without new acceleration methods allowing for future accelerators to be of reasonable size and cost, accelerator-based high-energy physics may reach an end. Plasmas can sustain very large longitudinal electric fields that can travel at velocities close to the speed of light. Large energy gains where demonstrated for electrons in plasma-based accelerators driven by intense laser pulses or short electron bunches. Research on the beam-driven, plasma wakefield accelerator (PWFA) scheme is experiencing an increasing interest. This is motivated by the 42GeV energy gain in 85 cm of plasma (50GeV/m accelerating gradient) demonstrated at SLAC [Blumenfeld, Nature 445, 741 (2007)]. Current PWFA experiments focus on two aspects: first, on the production of high quality accelerated bunches (narrow energy spread, low emittance, etc.) for example at SLAC FACET; second, on a new scheme based on the transverse self-modulation of long particle bunches in dense plasmas to resonantly drive wakefields [Kumar, Phys. Rev. Lett. 104, 255003 (2010)]. After briefly introducing the PWFA and the recent results I will focus on the second aspect and begin by introducing the physics of the self-modulation instability (SMI). I will discuss initial experiments at the Brookhaven National Laboratory Accelerator Test Facility that have shown that long electron bunches do indeed drive multiple period wakefields. They also suggest that the seeding of the self-modulation instability is possible. After presenting these results, I will describe experiments that we are planning at SLAC-FACET to study the physics of the SMI of electron and positron bunches. This experimental program is known as E209. Then I will describe the AWAKE project that was recently approved at CERN. AWAKE will use the long SPS, 400GeV bunch with 3x10^11 protons and a 10m-long plasma to address the issues related to driving GeV/m accelerating gradients over large distances to accelerate electrons to high energies in a single plasma section. This experiment will operate at lower gradient than other plasma-based accelerators, but aims at avoiding the staged-acceleration necessary when using drivers (laser pulse or particle bunch) carrying small amounts of energy. The SPS bunch carries ~20kJ, while LHC bunches carry more than 100kJ, more than necessary to produce an ILC-like electron bunch (2x10^10 e -500GeV or ~1.6kJ)! Operating at lower plasma density and therefore with a larger accelerating structure also eases the injection process and the beams generation and alignment tolerances. The purpose of the presentation is to give an overview of the experimental programs we are developing while explaining the basic concepts." [mehr]
"New degrees of freedom in optical design can be attained by introducing in the optical path phase discontinuities in addition to the usual propagation phase. This enables wavefront engineering with unprecedented flexibility, including a generalization of the classical laws of reflection and refraction and a wide variety of new planar optical components. These include aberration-free flat lenses and axicons, background free broadband wave platesand flat phase plates that create optical vortices." [mehr]
"A revision of our system of units, the SI, is currently discussed and may be implemented as early as 2018. The new SI is a logical extension of an argument made in 1983 when the meter was redefined to be based on the exact value of the speed of light. In the new SI all units will be derived from seven fundamental reference constants, thus replacing the seven base units of the current system.For example, the unit of mass, the kilogram, is currently defined by an artifact called the International Prototype of the Kilogram (IPK). In the future we will be able to realize the unit of mass, not just at the kilogram level, from a fixed value of the Planck constant, which has units of kg m^2/s.One condition for redefinition is agreement between different measurements of the Planck constant. Currently two measurement strategies lead to values with relative uncertainties less than 100 parts per billion (ppb): (1) Avogadro’s number can be determined by estimating the number of atoms in a well characterized crystal. From Avogadro’s number h can be calculated using the Rydberg constant, which is known with much smaller uncertainty (2) A watt balance can be used to measure mechanical power in units of electrical power. Electrical power can be measured as the product of the Planck constant and two frequencies by utilizing the Josephson effect and the Quantum Hall effect.NIST has carried out measurements of h with watt balances for over 20 years. In the past 18 months a new team has performed a largely independent determination of h. I will describe this measurement and measurements from other laboratories." [mehr]
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