Oscillations, Waves, and Interactions - GWDG

Applied physics at the “Dritte” 13
Lectures in all fields of vibrations and waves, usually supplemented by
experiments, have been a continual element of academic life at the “Dritte”.
Pottel’s idea lead to more than forty years of research into the molecular behaviour
of liquids [146,147]. Although other aspects, such as the dielectric [153,154] and ultrasonic
[155] relaxations of non-dipolar liquids, were also considered, attention was
predominantly directed towards hydrogen network fluctuations, self-associations, and
conformational variations in associating systems. Because of its omnipresence on our
planet, special attention was given to water in its different states of interaction.
More recently, critical phenomena and their crossover to the noncritical dynamics of
demixing binary and ternary liquids were (and still are) the focus of interest. Some
aspects are summarised in contributions to this book [146,147].
11 Hypersonic spectroscopy of solids
The discovery of surface excitation and detection by Baransky and by Bömmel and
Dransfeld in the late 1950s opened up new vistas for high-frequency ultrasonic investigations
of materials. Klaus Gottfried Plaß took the opportunity to develop
an ultrasonic spectrometer for liquid attenuation measurements up to GHz frequencies
[145]. Wolfgang Eisenmenger and his group performed a comprehensive investigation
of the hypersonic attenuation in cylindrical quartz rods up to 10 GHz [156].
Measurements at temperatures between 4 K and 273 K involved a helium liquefier
which subsequently was used in various low temperature investigations.
A breakthrough in phonon spectroscopy was reached by Eisenmenger during a stay
at Bell Telephone Laboratories in the summer 1966. Together with A. H. Dayem
he succeeded in quantum generation and detection of incoherent phonons, using
superconducting tunnel diodes [157,158]. Hypersonic measurements at frequencies
between 1 GHz and 1 THz were made possible by this pioneering work.