Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
14 results
Search Results
Item Open Access Zukunft der Optik(1970) Tiziani, Hans J.Die Optik hat in den letzten Jahren neuen Aufschwung genommen. Mitverantwortlich für diese Entwicklung sind sowohl die Verwendung von leistungsfähigen Computern als auch die Nachfrage nach immer besserer Auflösung und Bildqualität. Besonders positiv haben sich die Entwicklungen des Laser (1960) und der Holographie ausgewirkt. Immer neue Applikationen des gebündelten, kohärenten Laserlichtes werden erschlossen, doch will ich mich in diesem Zusammenhang auf die mögliche Weiterentwlckung der erwähnten Gebiete beschränken.Item Open Access Nuclear magnetic shielding tensors for 1H, 13C, and 15N in organic solids(1975) Spiess, Hans Wolfgang; Haeberlen, Ulrich; Kempf, Jürgen; Schweitzer, DieterA survey will be given of nuclear magnetic shielding tensors obtained by multiple pulse techniques for 1H in carboxylic acids and by high field NMR for 13C in carbonyl- and carboxyl groups of aromatic compounds and for 15N in pyridine and nitrobenzene.Item Open Access Speckling in diffraction patterns and optical images formed with the laser(1970) Hopkins, Harold H.; Tiziani, Hans J.It has been shown that the known characteristics of speckling in both diffraction patterns and optical images can be explained on the basis of a simple physical model. This explains not only the occurence of a predominant size but also the high contrast in speckle patterns.Item Open Access Energy relaxation and intervalley relaxation of hot electrons in n-type germanium(1966) Seeger, Karlheinz; Schweitzer, DieterThe average current density in n-type germanium subjected to superimposed strong ac and weak dc electric fields was both measured and calculated for frequencies of 9 and 35 GHz. Repopulation relaxation of the conduction band valleys and energy relaxation were taken into account. Experimental and theoretical result agree qualitatively.Item Open Access Resonance and relaxation attenuation by neutral acceptors in a magnetic field(1977) Schad, Hanspeter; Lassmann, Kurt; Zeile, HeinrichFine structure, level splitting, and relaxation times of the acceptor ground state in cubic semiconductors can be deduced from ultrasonic attenuation. By the application of a magnetic field it is possible to vary the coupling strength and the number of acceptors on speaking terms with the ultrasonic wave. Making use of this possibility, we have determined directly effective coupling constants for relaxation attenuation and the temperature dependence of the critical intensity for saturation of the resonant interaction. Results obtained for p-type GaAs and Si are discussed in comparison with analogous results for glasses.Item Open Access Measurement of small movements and vibrations by laser photography(1973) Tiziani, Hans J.Most of the holographic techniques applied so far for non-contacting measurements of surface displacements are highly sensitive. But the interpretation of the interference fringes obtained is usually rather difficult for a non-expert, especially for the study of tilts in the presence of lateral in-plane movements. Moire techniques could be applied to overcome some of the difficulties encountered but they require a relatively flat surface, which needs to be specially prepared. The application of speckling, a well-known phenomenon in coherent optics, was found to be very convenient for the investigation of lateral in-plane displacements and vibrations in the presence of tilts. The speckle pattern can be regarded ,as related to the object and hence will be displaced if the object or part of it is moved. For the analysis of in-plane movements or tilts the speckle pattern is photographed in the image plane or the Fourier transform plane of the object, respectively, before and after the movement has taken place. From the diffraction effects of the recorded speckle patterns the movement of the object is determined. Different techniques to measure rigid-body translations, tilts and surface vibrations will be demonstrated and a comparison with other methods given together with the appropriate experimental results.Item Open Access ODMR of phanes and charge transfer phanes(1979) Schweitzer, Dieter; Goldacker, Wilfried; Hausser, Karl H.; Staab, Heinz A.Triplet zero field splitted parameters |D| and |E| and decay rates ki of the triplet sublevels of two stereoisomeric tetramethoxy [2.2] paracyclophanes as well as those of two CT [2.2] paracyclophanes in low concentration in glasses and small neat single ctystals as measured by ODMR in zero fields at 1,3 K are presented.Item Open Access Anisotropy of phonon emission from hot electrons in germanium(1976) Reupert, Wolfram; Lassmann, Kurt; Groot, Peter deWe have measured quantitatively the anisotropy of the electron-acoustical phonon scattering in n-germanium in five directions of the (lTO) plane utilizing tunneling junctions for calibrated detection of the phonon radiation emitted from a small avalanche breakdown region in the germanium surface. For comparison and evaluation of phonon focusing a constantan heater and a tunneling junction were also used as phonon sources. A similar experiment has been reported by A. Zylbersztejn, but he could only compare the ratio of the amplitudes of longitudinal and transverse phonon pulses in a given crystal direction to the calculation.Item Open Access Dynamic nuclear polarisation in p-doped silicon by microwave ultrasonics(1969) Hausser, Karl H.; Schweitzer, DieterWe have investigated the dynamic nuclear polarisation (DNP) of 29 Si nuclei in highly doped silicon single crystals. The saturation of the electronic Zeeman levels in a magnetic field of 3.3 kG at 1.6°K was obtained using microwave ultrasonics of about 9 GHz. The ultrasonic waves were generated in a cavity by means of a transducer consisting of a thin film of CdS evaporated on the polished surface of the silicon. Preliminary results obtained with a silicon-rod of 2 x 2 x 12 mm cut with the long axis parallel to the (110) direction rendered a reduction of the NMR signal to about ⅓ in agreement with the expected negative sign of the DNP.Item Open Access High frequency phonon emission from superconducting Al-tunnelling junctions(1976) Eisenmenger, WolfgangIn single particle tunneling between identical superconductors phonons are generated by relaxation - and recombination transitions of injected quasiparticles. Phonon detection is mediated by the breaking of Cooper-pairs by phonons with energy exceeding the superconducting energy gap 2Δ D. This leads to an increase of the quasiparticle population and a corresponding contribution to the tunneling current in the thermal tunneling regime 0