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Physics & Astronomy
Ernst Knoesel Associate Professor Biography: Ph.D., Free University Berlin, Germany Field: Experimental Optical Physics THz (Terraherz) time-domain spectroscopy is applied to detect the complex dielectric properties of solid state materials and fluids at THz frequencies (1012 Hz). The analysis yields information on the properties of charge carriers (density and mobility) and on the structure and conductivity in fluids. Since THz EM-waveforms are generated by ultrafast laser pulses, electron lifetimes and recombination dynamics in dielectrics (quartz, sapphire) can be followed with picosecond temporal resolution (10-12 seconds) using pump-probe techniques. In this experimental field students will learn the use of ultrafast lasers, general optics and non-linear optics (second and third harmonic generation, THz generation), concepts of electronic excitation and relaxation mechanism in solids and fluids, data acquisition with computer interfaces and programming in LABVIEW. In collaboration with Prof. Chary (Chemistry) we investigate the variable temperature optical reflectance of quasi-low-dimensional crystals with show electronic instabilities. Materials with low-dimensional electronic correlations have long been known to exhibit interesting and often technologically important phenomenon such as high-temperature superconductivity, charge-density wave (CDW) driven phase transitions and magnetic order below a critical temperature. Our studies on low-dimensional molybdenum oxides have revealed for the first time the presence of anomalous oscillations in the reflectance spectra, which are interpreted as the existence of a surface domain. In the future we plan to extend our investigations on other materials, as well as uncovering the mystery of the nature of the surface domain.
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