Schwarzwald

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

Research interest:

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)
thesis title: “Modern Spectroscopy on Biological Molecules – Structure and Bonding investigated by THz time-domain and transient phase-grating spectroscopy“ (full text (PDF)
) (15 Mb)

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

  1. W. S. L. Lee, Korbinian Kaltenecker, S. Nirantar, W. Withayachumnankul, M. Walther, M. Bhaskaran, B. M. Fischer, S. Sriram, and C. Fumeaux
    "Terahertz near-field imaging of dielectric resonators"

    Opt. Express, 25 (4), 3756-3764 (2017)
    (abstract, pdf)

  2. K. J. Kaltenecker, A. Tuniz, S. C. Fleming, A. Argyros, B. T. Kuhlmey,  M. Walther, and B. M. Fischer
    "Ultra-broadband perfect imaging in THz wire media using single-cycle pulses"
    Optica, 3(5), 458-464 (2016)
    (abstract, pdf)

  3. K. J. Kaltenecker, J. C. König-Otto, M. Mittendorff, S. Winnerl, H. Schneider, M. Helm, H. Helm, M. Walther, and B. M. Fischer
    "Gouy phase shift of a tightly focussed radially polarized beam"
    Optica, 3(1), 35-41 (2016)
    (abstract, pdf)

  4. A. Stoppa, A. Nazet, A. Thoman,  M. Walther, and R. Buchner
    "Dielectric Response and Collective Dynamics of Acetonitrile"
    J. Mol. Liqu., 212, 963-968 (2015)
    (abstract, pdf)

  5. J. Wallauer, C. Grumber, V. Polyakov, R. Iannuc, V. Cimalla, O. Ambacher, and  M. Walther
    "Large area InN terahertz emitters based on the lateral photo-Dember effect"
    Appl. Phys. Lett., 107, 111102 (2015)
    (abstract, pdf)

  6. V. A. Fedotov, J. Wallauer,  M. Walther, M. Perino, N. Papasimakis, and N. I. Zheludev
    "Wavevector Selective Metasurfaces and Tunnel Vision Filters"
    Nature | Light: Science & Applications, 4, e306 (2015); doi: 10.1038/lsa.2015.79.
    (abstract, pdf)

  7. T. Sonnleitner, D. A. Turton, G. Hefter, A. Ortner, S. Waselikowski,  M. Walther, K. Wynne, and R. Buchner
    "Ultra-Broadband Dielectric and Optical Kerr-Effect Study of the Ionic Liquids Ethyl and Propylammonium Nitrate"
    J. Chem. Phys. B 119, 8826-8841 (2015)
    (abstract, pdf)

  8. L. Öhrström, B. Fischer, A. Bitzer, J. Wallauer,  M. Walther, and F. Rühli
    "Terahertz Imaging Modalities of Ancient Egyptian Mummified Objects and a Naturally Mummified Rat"
    Anatomical Record, 298 (6), 1135-1143 (2015)
    (abstract, pdf)

  9. J. Wallauer, C. Grumber, and M. Walther
    "Mapping the coupling between a photo-induced local dipole and the eigenmodes of a terahertz metamaterial"
    Opt. Lett., 39 (21), 6138-6141 (2014)
    (abstract, pdf)

  10. T. Sonnleitner, D. A. Turton, S. Waselikowski, J. Hunger, A. Stoppa, M. Walther, K. Wynne, and R. Buchner
    "Dynamics of RTILs: A comparative Dielectric and OKE study"

    J. Mol. Liq., 192, 19-25 (2014)
    (abstract, pdf)

  11. J. Wallauer and M. Walther
    "Fano line shape and phase reversal in a split-ring resonator based metamaterial"
    Phys. Rev. B, 88, 195118 (2013)
    (abstract,pdf)

  12. A. Tuniz, K. Kaltenecker, B. M. Fischer M. Walther, S. C. Fleming, A. Argyros, and B. Kuhlmey
    "Metamaterial fibres for subdiffraction imaging and focusing at terahertz frequencies over optically long distances"
    Nature Comm., 4, 2706 (2013)
    (abstract,pdf)

  13. O. Buchnev, J. Wallauer, M. Walther, M. Kaczmarek, N. I. Zheludev, and V. A. Fedotov
    "Controlling intensity and phase of terahertz radiation with an optically thin liquid crystal-loaded metamaterial"

    Appl. Phys. Lett. 103, 141904 (2013)
    (abstract, pdf)

  14. I. Al-Naib, C. Jansen, R. Singh, M. Walther, and M. Koch
    "Novel THz Metamaterials Designs: From Near and Far Field Coupling to High Q Resonances"

    IEEE Trans. Terahertz Sci. Technol., 3, 772-782 (2013)
    (abstract, pdf)

  15. S. Waselikowski, C. Fischer, J. Wallauer, and M. Walther
    "Optimal plasmonic focusing on a metal disc under radially polarized terahertz illumination"

    New J. Phys., 15, 075005 (2013)
    (abstract, pdf)

  16. W. Withayachumnankul, C. M. Shah, C. Fumeaux, K. Kaltenecker, M. Walther, B. M. Fischer, D. Abbott, M. Bhaskaran, and S. Sriram
    "Terahertz localized surface plasmon resonances in coaxial microcavities"
    Adv. Opt. Mat., 1 (6), 412 (2013)

    (abstract, pdf)

  17. A. Turton, T. Sonnleitner, A. Ortner, M. Walther, G. Hefter, K. R. Seddon, S. Stana, N. V. Plechkova, R. Buchner, and K. Wynne
    "Structure and dynamics in protic ionic liquids: A combined ultrafast optical Kerr-effect and dielectric relaxation spectrocopy study"
    Faraday Discuss., 154, 145-153 (2012)

    (
    abstract, pdf)

  18. B. Ung, M. Rozé, A. Mazhorova, M. Walther, and M. Skorobogatiy
    "Suspended core subwavelength plastic fibers for terahertz guidance"

    Optics & Photonics News (OPN), 22 (12), 41 (2011)
    (abstract)

  19. J. Wallauer, A. Bitzer, S. Waselikowski, and M. Walther
    "Near-field signature of electromagnetic coupling in metamaterial arrays: A terahertz microscopy study"

    Opt. Express, 19 (18), 17283-17292 (2011)
    (abstract, pdf)

  20. M. Franz, B. M. Fischer, and M. Walther
    "Probing structure and phase-transitions in molecular crystals by terahertz time-domain spectroscopy"
    J. Mol. Struct., 1006, 34-40 (2011)

    (abstract, pdf)

  21. M. Rozé, B. Ung, A. Mazhorova, M. Walther, and M. Skorobogatiy
    "Suspended core subwavelength fibers: practical designs for low-loss terahertz guidance"

    Opt. Express, 19 (10), 9127-9138 (2011)
    (abstract, pdf)

  22. M. Walther and A. Bitzer
    "Electromagnetic wave propagation close to microstructures studied by time and phase-resolved THz near-field imaging"
    Int. J. Infrared Millimeter Waves, 32 (8-9), 1020-1030 (2011)
    (abstract, pdf)

  23. A. Bitzer, A. Ortner, H. Merbold, T. Feurer, and M. Walther
    "Terahertz near-field microscopy of complementary planar metamaterials: Babinet's principle"

    Opt. Express 19 (3), 2537-2545 (2011)
    (abstract, pdf)

  24. D. A. Turton, J. Hunger, A. Stoppa, A. Thoman M. Candelaresi, G. Hefter, M. Walther, R. Buchner, and K. Wynne
    "Rattling the cage: Micro-to mesoscopic structure in liquids as simple as argon and as complicated as water"
    J. Mol. Liq. 159 (1), 2-8 (2011)
    (
    abstract, pdf)

  25. S. Waselikowski, K. Kratt, V. Badilita, U. Wallrabe, J. G. Korvink, and M. Walther
    "Three-dimensional microcoils as terahertz metamaterial with electric and magnetic response"
    Appl. Phys. Lett. 97, 261105 (2010)
    (abstract, pdf)

  26. V. A. Fedotov, N. Papasimakis, E. Plum, A. Bitzer, M. Walther, P. Kuo, D. P. Tsai, and N. I. Zheludev
    "Spectral collapse in ensembles of metamolecules"
    Phys. Rev. Lett. 104, 223901 (2010)
    (abstract, pdf)


  27. L. Öhrström, A. Bitzer, M. Walther, and F. J. Rühli
    "Terahertz imaging of ancient mummies and bone"

    American Journal of Physical Anthropology 142 (3), 497-500 (2010)
    (abstract, pdf)


  28. A. Bitzer, A. Ortner, and M. Walther
    "Terahertz near-field microscopy with subwavelength spatial resolution based on photoconductive antennas"

    Applied Optics 49 (19), E1-E6 (2010)
    (abstract, pdf)

  29. M. Walther, B. M. Fischer, A. Ortner, A. Bitzer, A. Thoman, and H. Helm
    "Chemical sensing and imaging with pulsed terahertz radiation"

    Anal. Bioanal. Chem. 397 (3), 1009-1017 (2010)
    (abstract, pdf)

  30. M. Walther, A. Ortner, H. Meier, U. Löffelmann, P. J. Smith, and J. G. Korvink
    "Terahertz metamaterials fabricated by inkjet printing"
    Appl. Phys. Lett. 95, 251107 (2009)
    (abstract, pdf)

  31. A. Bitzer, J. Wallauer, H. Helm, H. Merbold, T. Feurer, and M. Walther
    "Lattice modes mediate radiative coupling in metamaterial arrays"

    Opt. Express 17 (24), 22108-22113 (2009)
    (cover movie, abstract, pdf)

  32. D. A. Turton, J. Hunger, A. Stoppa, G. Hefter, A. Thoman, M. Walther, R. Buchner, and K. Wynne
    "Dynamics of Imidazolium Ionic Liquids from a Combined Dielectric Relaxation and Optical Kerr Effect Study: Evidence for Mesoscopic Aggregation"
    J. Am. Chem. Soc. 131, 11140-11146 (2009)
    (
    abstract, pdf)

  33. A. Knübel, R. Aidam, V. Cimalla, L. Kirste, M. Baeumler, C.-C. Leancu, V. Lebedev, J. Wallauer,  M. Walther, and J. Wagner
    "Transport characteristics of Indium Nitride (InN) films grown by plasma assisted molecular beam epitaxy (PAMBE)"
    phys. stat. sol. (c), 6 (6), 1480-1483 (2009)
    (cover,
    abstract, pdf)

  34. A. Bitzer, H. Merbold, A. Thoman, T. Feurer, H. Helm, and M. Walther
    "Terahertz near-field imaging of electric and magnetic resonances of a planar metamaterial"

    Opt. Express, 17 (5), 3826-3834 (2009)
    (abstract, pdf)

  35. J. Hunger, A. Stoppa, A. Thoman, M. Walther, and R. Buchner
    "Broadband Dielectric Response of Dichloromethane"

    Chem. Phys. Lett. 471, 85-91 (2009)
    (abstract, pdf)

  36. A. Bitzer and M. Walther
    "Terahertz near-field imaging of metallic subwavelength holes and hole arrays"
    Appl. Phys. Lett. 92, 021107 (2008)
    (abstract, pdf)

  37. A. Thoman, A. Kern, H. Helm, and M. Walther
    "Nanostructured gold films as broadband terahertz antireflection coatings"
    Phys. Rev. B 77 (19), 195405 (2008)
    (abstract, pdf)


  38. A. Kern and M. Walther
    "Subgridding in the FDTD method for simulating the interaction of terahertz radiation with metal"
    J. Opt. Soc. Am. B 25 (3), 279-285 (2008)
    (abstract, pdf)


  39. A. Bitzer, H. Helm and M. Walther
    "Beam-Profiling and Wavefront-Sensing of THz Pulses at the Focus of a Substrate-Lens"
    IEEE J. Select. Top. Quant. Electron. 14 (2), 476-481 (2008)
     (abstract, pdf)

  40. M. Franz, B. M. Fischer, and M. Walther
    "The Christiansen effect in terahertz time-domain spectra of coarse-grained powders"
    Appl. Phys. Lett. 92 (2), 021107 (2008)
    (abstract, pdf)

  41. M. Walther, D. G. Cooke, C. Sherstan, M. Hajar, M. R. Freeman, and F. A. Hegmann
    "Terahertz conductivity of thin gold films at the metal-insulator percolation transition"
    Phys. Rev. B 76 (12) 125408
    (2007)
    (abstract, pdf)

  42. A. Bitzer, M. Walther, A. Kern, S. Gorenflo, and H. Helm
    "Examination of the spatial and temporal field distributions of single-cycle terahertz pulses at a beam focus"
    Appl. Phys. Lett. 90 (7), 071112 (2007)
    (abstract, pdf)

  43. M. Walther, M. R. Freeman, and F. A. Hegmann
    "Metal-wire terahertz time-domain spectroscopy"
    Appl. Phys. Lett. 87 (26), 261107 (2005
    (abstract, pdf)


  44. M. Walther, G. S. Chambers, Z. Liu, M. R. Freeman, and F. A. Hegmann
    "Emission and detection of terahertz pulses from a metal tip antenna" 
    J. Opt. Soc. Am. B 22 (11), 2357-2365 (2005
    (abstract, pdf)

  45. M. Walther, V. Raicu, J. P. Ogilvie, R. Phillips, R. Kluger, and R. J. D. Miller
    "Determination of Fe-CO bond energy in myoglobin using heterodyne detected transient thermal phase grating spectroscopy"
    J. Phys. Chem. B 109, 20605-20611 (2005) 
    (abstract, pdf)


  46. M. Walther, B. M. Fischer, and P. Uhd Jepsen
    "Noncovalent intermolecular forces in polycrystalline and amorphous saccharides in the far infrared"
    Chemical Physics 288 261-268 (2003)
    (abstract, pdf)

  47. B. M. Fischer, M. Walther, and P. Uhd Jepsen
    "Far-infrared vibrational modes of DNA components studied by terahertz time-domain spectroscopy"
    Phys. Med. Biol. 47 3807 (2002)
    (abstract, pdf)


  48. M. Walther, P. Plochocka, B. Fischer, H. Helm, and P. Uhd Jepsen
    "Collective Vibrational Modes in Biological Molecules investigated by THz Time-Domain Spectroscopy" 
    Biopolymers (Biospectroscopy), 67 (4-5),  310-313 (2002)
    (abstract, pdf)


  49. M. Schall, M. Walther, and P. Uhd Jepsen
    "Fundamental and second-order phonon processes in CdTe and ZnTe"
    Phys. Rev. B 64 (9) 094301 (2001)
    (abstract, pdf)


  50. M. Walther, B. Fischer, M. Schall, H. Helm, and P. Uhd Jepsen
    "Far-infrared vibrational spectra of all-trans, 9-cis and 13-cis retinal measured by THz time-domain spectroscopy"
    Chem. Phys. Lett., 332, 389-395 (2000)
    (abstract, pdf)


  51. M. Walther, K. Jensby, S. R. Keiding, H. Takahashi, and H. Ito
    "Far-infrared properties of DAST"
    Opt. Lett., 25 (12), 911 (2000)
    (abstract, pdf)


  52. C. Winnewisser, F. Lewen, M. Schall, M. Walther, and H. Helm
    "Characterization and application of dichroic filters in the 0.1 to 3 THz region"
    IEEE Trans. Microwave Theo. Tech., 48 (4), 744 (
    2000)
    (abstract, pdf)
Invited talks
Conference contributions

THz Freiburg THz Group Freiburg


My time in Canada