Space-Time Physics in QUEST: Basics, Experiments and Technologies
07.10.2009
Fundamental constants and the realization of units
Fritz Riehle, PTB
To be able to compare the measurements with highest accuracy obtained at different locations or at different times the measurements have to be conducted in a universal and accepted system of units. In the first lecture, an introduction to the International System of Units (SI) will be given together with its evolution dictated by the fast progress in measurement technology and the needs of industry, science and technology. The basic properties of the SI will be outlined at the example of the candela as one of its seven base units. The second part of this lecture will concentrate on the currently attempted transition to a system based on fundamental constants rather than on material artefacts.
14.10.2009
Electrical Units
Fritz Riehle, PTB
Quantum effects like the Josephson effect and the quantum Hall effect allows one to relate electrical and other units to frequency measurements which are by far the most accurate measurement techniques. In this lecture the basics of these two effects will be outlined and their relation to the SI will be contrasted with the current definition of the ampere as the base unit of electric current. The second part of this lecture will deal with most accurate experiments conducted with superconducting quantum interferometric devices (SQUIDS) based on the Josephson effect. Particular emphasis will be laid on the similarities and differences between electron interferometry and other kinds of matter wave interferometry.
21.10.2009
Mass and related quantities
Fritz Riehle, PTB
In the current SI, the base unit of the mass, the kilogram, is defined via an artefact i.e. the international kilogram prototype which seems to have changed its mass during the past decades. In this lecture novel approaches to base the mass unit on fundamental constants will be explained and discussed like the watt balance and the associated most accurate determination of Planck's constant. The measurement of atomic masses and mass ratios by ion traps and mass spectrometry will complement the lecture.
28.10.2009
Linking Chemistry with Physics
Fritz Riehle, PTB
The Mole as the base unit for the amount of substance links the measurements in the fields of physics and chemistry. In the first part of this lecture the International Project will be discussed in some detail where Avogadro's number is determined by using an 28Si sphere using X-ray interferometric, optical and mechanical precision methods. In the second part of the lecture the current quantum optical and other high precision experiments will be discussed that will allow one to define the Kelvin as the base unit of temperature via the Boltzmann constant and abandon the current definition based on the triple point of water.
04.11.2009
Time, Frequency and Length
Fritz Riehle, PTB
Time and frequency measurements allow by far for the highest accuracy in basic and applied metrology. This lecture will start with an introduction to the basics of atomic clocks and atomic time scales. Based on the fundamental constant of the speed of light the methods of highly precise length measurements will be outlined for long and short distances. Particular emphasis will be laid on the questions that are at the heart of QUEST i.e. the influence of General Relativity on the most accurate time and length measurements and on experiments that allow one to test the validity of these assumptions.
11.11.2009
Optical Clocks and the future of time measurements
Fritz Riehle, PTB
The rapid progress with novel optical atomic clocks that are superior to the best caesium clocks with respect to the attainable accuracy and stability will require a future new definition of the second as the base unit of time in the SI. The lecture will first concentrate on optical clocks with neutral atoms and single ions and the attempts to solve fundamental questions. Among them is the possible drift of fundamental constants with time with its impact on the newly devised Quantum SI. The last part of the lecture will deal with novel and unconventional methods of time and frequency transfer that are capable to make full use of the properties of optical clocks and that are an active research field in QUEST.
25.11.2009
Overview of time scales and laser induced phenomena
Manfred Lein, ITP
The various types of motion of the electrons and nuclei in molecules occur on time scales ranging from picoseconds down to attoseconds. The most convenient tool for the observation of ultrafast phenomena in the femtosecond and attosecond regime consists of using ultrashort laser pulses both to start and to probe dynamics. Ultrashort pulses can be made very intense, leading to a multitude of laser-induced phenomena. We give an overview of laser induced processes with focus on strong laser fields. This includes multiphoton and tunneling ionization, laser-induced dissociation and Coulomb explosion, high-order harmonic generation.
02.12.2009
High order harmonic generation
Manfred Lein, ITP
The generation of coherent radiation in the extreme ultraviolet regime is named high-order harmonic generation (HHG). It is a by-product of laser-matter interactions and very useful as a light source because of the high frequency and since it can be used to make attosecond pulses. We discuss in detail the mechanism and the theory of HHG. This includes the semiclassical three-step model of HHG (ionization, acceleration and recombination), the strong-field approximation (the quantum mechanical version of the three-step model) as well as direct numerical approaches.
09.12.2009
Molecular Imaging
Manfred Lein, ITP
The response of molecules to strong laser fields is highly sensitive to the molecular properties. Laser-induced phenomena can therefore be used to image the structure and dynamics of molecules. We distinguish three approaches by the sort of observed particles: electrons, ions or photons. When observing electrons, one can study diffraction from molecules with their own electrons. Ions from Coulomb explosion yield a picture of the molecular geometry before fragmentation. When observing photons, molecular orbitals can be approximately reconstructed from HHG spectra.
13.01.2010
Laser development for precision metrology
Peter Weßels, LZH
In this lecture, the current status of laser research carried out at the LZH within the QUEST research area D "enabling technologies" will be reviewed. Different types of precision metrology demand for different, specialized laser sources tailored for the specific type of measurement. The different demands and the realized solutions will be demonstrated on a couple of exemplary laser solutions. These will range from single-frequency laser systems for the second generation of gravitational wave detectors over specially designed fiber components needed e.g. for high efficiency amplifier solutions up to the demands set by the laser development for space based lasers.
20.01.2010
Limitations in high power fiber amplifiers
Peter Weßels, LZH
For the third generation of gravitational wave detectors, the output power of the current lasers systems will have to be scaled up towards 1 kW. To reach this goal, fiber amplifiers seem to be a good approach as the beam quality is mainly determined by the fiber design and the excellent spectral properties of a low power seed source can be maintained in the amplification process. However, due to the long interaction length and high intensities within the fiber core, the output power is finally limited by nonlinear scattering processes like stimulated Brillouin scattering (SBS). In this lecture, the effect of SBS will be discussed and its impact on fiber amplifier performance and the degradation of the several beam parameters will be shown on the example of Ytterbium doped fiber amplifiers. I will present different methods for the characterization and possible approaches for the suppression of the SBS process.
27.01.2010
Laser sources for 3rd generation gravitational wave detectors
Peter Weßels, LZH
While 1064 nm laser sources are used for the first and second generation of gravitational wave detectors, the final wavelength for the third generation is not chosen yet. As silicon is considered as mirror substrate material, one option is to change to the 1.55 µm range due to the high transmission of silicon in this wavelength range. In this lecture, I will present recent results on the fiber amplifier development around 1.55 µm. In the first part of the lecture, the fundamentals of the Erbium ion in glass, which is used as the laser active material, will be discussed. Although this material is well understood in the small signal regime due to its use by the telecom industry, there are still a lot of challenges to achieve high output powers above 100 W. Thus, I will present both investigations carried out in the low power regime to understand the basic properties of these amplifiers as well as the latest results in the high power amplification. Finally, in order to achieve high output power stability, an active control loop for power noise reduction will be necessary for all laser systems considered for gravitational wave detectors. To understand the controllability of such fiber amplifiers, a theoretical model and corresponding experiments about the systems reaction to pump and seed variations will be presented.
