3.2 Solids and Nanostructures: Electrons, Spins, and Phonons

We generate short pulses with wavelengths longer than about 10 μm (corresponding to frequencies below 30 THz) and use them to study transitions in solids in this frequency range (e.g., intersubband transitions in semiconductor nanostructures, interlevel transitions in impurities, interband transitions in narrow-gap materials, and intraband transitions).

Ultrashort laser pulses offer unique capabilities for direct material modification on the micro- and nano- scales. In wide bandgap materials (such as crystal and glasses), tightly focusing sub-ps laser pulses provides peak intensities able to trigger the formation of an electron-hole plasma in the bulk of the target. The energy stored in the plasma fuels subsequent structural material modifications resulting in permanent changes of the refractive index in the irradiated region. The ambition of the topic dual: provide useful insights into the laser-induced plasma formation (taking place intrapulse) when focusing a fs-laser pulse in the volume of a solid dielectric and exploit the laser-induced refractive index changes to fabricate functional devices such as complex micro-optical photonic structures (optical chips) for (bio-)sensing applications

We investigate the fundamental limits of optoelectronic devices in terms of emission power, efficiency and reliability. The focus of our experimental work is the analysis of materials and devices that are relevant as optoelectronic emitters such as diode lasers and their gain media, e.g. quantum-well or quantum-dot structures. Understanding the relaxation processes of non-equilibrium carriers measured by transient spectroscopy helps to answer questions about intrinsic and extrinsic limitations of the gain materials and device structures.

We investigate how magnetic order is manipulated by femtosecond laser excitation. Our studies are focused on fundamental processes on ultrafast time and nanometre length scale. In addition to all-optical spectroscopy we use novel light sources like free electron laser and high harmonic sources in the extreme ultraviolet spectral range to probe the transient magnetic state with element-specificity and nanometre spatial resolution.

Photonics is the science and technology of the harnessing of light. It lies at the confluence of various disciplines: optics, material science, electrical engineering, nanotechnology, physics, and chemistry. Within this context, our research focusses on the theory of light propagation and light-matter interaction in complex optical and photonic systems. This includes the development of advanced computational and analytical approaches and their application to specific systems. Our mission is to: Discover and investigate novel physical effects; Develop concepts and designs for advanced photonic materials and functional elements; Provide interpretative as well as predictive support for experiments.