Dr. Markus Walther
Molecular and Optical Physics
Physikalisches Institut
Albert-Ludwigs-Universität
Hermann-Herder-Str. 3
79104 Freiburg
Germany
Phone: (+49) 203 5721
Fax: (+49) 203 5955
email: walther@physik.uni-freiburg.de
Terahertz time-domain
spectroscopy (THz-TDS) is a useful extension of traditional
far-infrared spectroscopic methods. It allows the direct determination
of the optical properties (absorption, refractive index, conductivity, permittivity etc.) of a
variety of
samples in the submillimeter wavelength range. The technique
relies on the coherent generation and detection of ultra-short
electromagnetic transients using femtosecond laser pulses. Due to their
duration of less than a picosecond THz pulses exhibit a large frequency
bandwidth extending from a few GHz up to some THz (1 THz = 33 cm-1
= 4.1 meV), thereby allowing broadband and time-resolved spectroscopy
in the far-IR.
We study the characteristic THz spectra of individual biomolecular
systems in the crystalline phase. In particular the
correlation between the observed low-frequency modes and molecular
structure and association is investigated. Our results show that the
modes in the THz region represent a unique fingerprints for the
molecular structure and conformation, allowing to distinguish related
compounds. It has
been demonstrated, that the method can be used to even discriminate
between different
Isomeric conformations of a molecule, as in the case of retinal. Potential applications in
chemical
recognition and drug screening are feasible.
Another powerful application based on the coherent emission and detection of pulsed THz radiation is THz imaging. The technique can for example be used to produce spectrally resolved transmission images of dry objects (e.g. suitcases for security screening, packaged goods for industrial applications, or mummyfied tissue in archeology - see publictions section). However, due to the large THz-wavelengths spatial resolution in far-field imaging is limited to millimeters. We have recently developed a near-field scanning technique based on utilizing photoconductive antennas as THz near-field probes. In this approach the spatial resolution is no longer diffraction limited, but is solely given by the potential resolution provided by the probe. In our case a sub-wavelength spatial resolution of λ/25 has been achieved.
| Short Curriculum Vitae |
| 1992-1999 |
Studies
in Physics und Mathematics at the Albert-Ludwigs Universität,
Freiburg (Germany) |
| 1994-95 |
ERASMUS-scholarship
at the University of Glasgow (GB) |
| 1999 |
Staatsexamen
in physics and mathematics at Freiburg University |
| Sept.
1999 |
Visiting researcher at the Dep.
of Physics and Chemistry, University of Arhus (Denmark), group of
Prof. S. R. Keiding |
| 1999 |
Diploma
in physics, University Freiburg Thesis title: “Resonant excitation of biomolecules and solids in the Terahertz Frequency range“ |
| 2000-2003 |
PhD studies at the University of Freiburg (Germany) in the group of P. Uhd Jepsen/Prof. H. Helm |
| 2002 |
Visiting researcher
at the Dep. of Chemistry and Physics, University of Toronto (Canada), group of Prof. R. J. Dwayne Miller |
| 2003 |
PhD
in physics at the Albert-Ludwig University Freiburg (Germany) |
|
2004-2006 |
Postdoctoral Fellow
at the University of Alberta, Edmonton, Canada in the Ultrafast Spectroscopy Group of Prof. Hegmann |
| since June 2006 | THz-Group leader at the University of Freiburg / Germany |
| 2011 | Habilitation in Physics at the University Freiburg |
| Publications |
| Invited talks |
| Conference contributions |
THz Group Freiburg