Universität Stuttgart
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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 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 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 Phonon detection by the fountain pressure in superfluid 4Helium films(1980) Eisenmenger, WolfgangThe importance of phonon focussing was first demonstrated by Taylor, Maris and Elbaum, who calculated the phonon intensities or different modes in single crystals from the detailed form of the angle or k-dependent sound velocity surfaces. The results of these calculations are well-confirmed by experiment. It is quite surprising that phonon focussing leads in several crystals to very narrow beams of phonon energy propagation especially for transverse modes, as recently calculated by Rosch and Weis, who presented their computer results in a very instructive form. From these theoretical results it appears worthwhile to devise methods by which the intensity distribution of incoherent phonons propagating in single crystals can be measured in detail or directly imaged.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 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 Phonon scattering at acceptors with gamma8 ground states in semiconductors(1980) Sigmund, Ernst; Lassmann, KurtThe ground state of acceptors in cubic semiconductors is fourfold degenerate and the interaction with the lattice vibrations leads to the possibility of a Jahn-Teller effect, causing a dynamical splitting of the electronic levels. However, due to the extended nature of the wave function of the defect, random internal fields may have dominant influence to destroy the J.T. effect. Such an influence should be smaller for deeper acceptors, where the wavefunctions are more concentrated.Item Open Access 15N and 13C spin lattice relaxation in neat liquids at high magnetic fields(1975) Schweitzer, Dieter; Spiess, Hans WolfgangGeneral features of 15N spin lattice relaxation in nitrobenzene, pyridine and triethanolamine are discussed and compared with l3C relaxation mechanisms.Item Open Access Image quality criteria for aerial survey lenses(1978) Tiziani, Hans J.An image quality criterion based on MTF is highly desirable. The quality specification should be appropriate for the application of the optical system and simple for the user. The proposed quality criteria look promising and comparisons with subjective image quality techniques commonly used are favourable. Further evaluations are needed before quality specification can be recommended.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.