Research - Forschung

UNDER CONSTRUCTION Jan/Feb 2012 - I am sorry for any inconvenience due to the rearrangement of my website.

Nano-world: from molecules to living cells
Nano-Welt: von Molekülen zu lebenden Zellen

Chemical imaging, microscopes, nanoscopes, infrared and terahertz waves
Chemische Bildgebung, Mikroskope, Nanoskope, Infrarot und Terahertz Wellen

past and present	Terahertz (THz) research Infrared (IR) research see below
	NASA mission (Sept. 1993: photos) on the Kuiper Airborne Observatory ( KAO), Ames, California. Observation flights in astronomy: study fine-structure emission lines of N+ at 205 µm (1.46 THz) in objects DR21, S106, W49. Further reading - references on N+: J. M. Brown et al., ApJ 428, L37 (1994): The fine-structure intervals of (N-14)+ by far-infrared laser magnetic resonance, COBE FIRAS full sky map of N+ at 205 µm (1.46 THz, see Fig. 1 of the publication).
	Terahertz Laser Chapter 6: E. Bründermann "Widely Tunable Far Infrared Hot Hole Semiconductor Lasers", 279 - 350 (2004) ISBN: 0-471-39200-6 in Long-wavelength Infrared Semiconductor Lasers. Germanium Laser (RSI 76, 063110)
	THz germanium lasers U.S. Patent 6,011,810 (2000), E. E. Haller, E. Bründermann Technology transfer Milestones
	Multilayer mirrors (1D photonic band gap material, Bragg mirrors): APL 83, 4119 Cavity enhanced - Resonator (CE) and ATR: Attenuated total reflection: APL 86, 201116
	Quantum Cascade Laser (QCL) Opt. Express 14 Photonik (in color/in German): Animation
	Camera - Array technology Time-Domain (THz TDS): abstract Coherent Synchrotron Radiation (THz CSR): Presentation
	Imaging/Spectroscopy Imaging - Scanning NASA - Gas - Plasma Liquid

Infrared (IR) research Laser microscopy: Presentation, Near-field microscopy / SNIM Applications of semiconductor terahertz lasers in biomolecular spectroscopy and imaging Proc. SPIE 6194, 619406 (2006) - Conf. 6194: Millimeter-Wave and Terahertz Photonics, Strasbourg, April 6, 2006 (invited) - Link to pdf at SPIE. COVER - Article: SNIM - Scanning near-field infrared microscopy Annu. Rep. Prog. Chem. C104, 235 - 255 (2008).

Currently I am a permanent staff scientist and researcher. Teaching is a major part of my work starting with students in their second year. My long-term interest is in how electromagnetic waves are influenced by geometry. This leads naturally to microscale and nanoscale materials as well as artificial materials. I am further interested in developing new experimental methods to answer questions posed in biophysical chemistry and in medicine at the crossroads of such disciplines. My access to THz semiconductor lasers led to a THz applications sub-group in the department. In addition, I initiated imaging and microscopy based technology to combine spatial and spectroscopic information. The technique for nanoscopic investigations has been motivated by a paper of Fritz Keilmann (MPI for Biochemistry): "FIR microscopy", Infrared Phys. Technol. 36, 217-224 (1995), which was presented at CIRP (see also in the same issue my PhD thesis results: E. Bründermann et al., "Mode fine structure of the FIR p-Ge Intervalenceband Laser measured by Heterodyne Mixing Spectroscopy with an optically pumped ring gas laser", Infrared Phys. Technol. 36, 59-69 (1995)). We currently use near and mid infrared lasers developed within the department of physical chemistry II for microscopic and nanoscopic experiments.

Experiments in the THz frequency range provide exciting science with the potential for a variety of applications not only in science but also for every-day-life. The unique powerful Ge THz laser, a semiconductor laser with a wide frequency tuning range from 1 to 4 THz, is able to explore potential applications. For more details refer to my web-based presentation.

The germanium laser devices are used in laboratory based applications. Another potential application of THz semiconductor lasers is found on airborne and spaceborne platforms to study the upper atmosphere (e.g. the ozone depleter molecule OH at 2.5 and 3.5 THz) or fine-structure lines and rotational states of molecules in star-forming regions of the universe (see my part in a NASA mission).

The study of proteins in their natural environment, in aqueous solution, is difficult in the THz region due to the high absorption of water. We have developed a high power THz germanium laser spectrometer which is able to measure THz absorptions precisely between 1 and 4 THz: New p-Ge THz spectrometer for the study of solutions: THz absorption spectroscopy of water, Rev. Sci. Instr. 76, 063110 (2005). This enables us to study biomolecules in their natural environment and directly observe solvation and collective motions.

Previously, we have reported the extension of SNIM as a label free method for the characterization of surfaces and subsurface structure in the chemically important O-H and C-H stretching (fingerprint region) on nm scales: Set-up of a SNIM: Imaging of sub-surface nano-structures, PCCP 8, 753 (2006). Our recent results demonstrate the high sensitivity of SNIM for label free characterization of functional groups in thin films and micro-structured self assembled monolayers (SAMs).

We have developed a label free technique to monitor intracellular water in single cells by near infrared micro-spectroscopy on the overtone transition of water around 1400 nm. Oxidative stress, addition of hormones and substances like insulin can alter the water concentration in cells. The intracellular water concentration is directly connected to the change of proteolysis or signal transduction (D. Häussinger, Biochem. J. 313, 697 (1996)). As a proof of principle we measured intracellular water concentration changes in hepatocytes. We observed cell swelling and shrinking due to changes in the intracellular water concentration (Erik Bründermann et al., Cover & Hot Article). This work was featured in Chemical Science and Chemistry World News of the Royal Society of Chemistry. For further details on infrared microscopy of living cells see also the press release and more information on my website.