Research

The research group led by Robert Huber conducts research in the fields of optical coherence tomography (OCT), non-linear imaging and laser physics. Here, work is mainly done on novel pico second lasers and on Fourier domain mode-locked (FDML) lasers. This laser concept was developed by Robert Huber and enables the realization of particularly fast tunable laser light sources. The research focus here is on further technological development, understanding of the physical processes and also on the implementation of FDML lasers for OCT applications. Besides OCT, FDML lasers are also used for nonlinear imaging and spectroscopy.

Another focus is on optical coherence tomography with tunable light sources (swept source OCT, SS-OCT). Here, among other applications, the in-house developed FDML lasers are used for ultrafast imaging to generate cross-sectional images of biological tissues such as skin or eye. Due to the high tuning rate, applications like VR-OCT, which displays entire volumes in a virtual environment with real-time video repetition rates, are possible.

With non-linear optical imaging, the group is pursuing further imaging techniques. Research areas are in time-encoded (TICO) Raman spectroscopy and microscopy, two-photon fluorescence microscopy (TPEF), and two-photon single-pulse fluorescence lifetime imaging (SP-FLIM). These techniques use novel pico second lasers that are also being researched and developed in the group.

Our main research topics:

Publications

2005

Robert Huber, Thomas Köhler, Martin O. Lenz, Ernst Bamberg, Rolf Kalmbach, Martin Engelhard, and Josef Wachtveitl,
pH-dependent photoisomerization of retinal in proteorhodopsin., Biochemistry , vol. 44, no. 6, pp. 1800-1806, 01 2005.
DOI:10.1021/bi048318h
Bibtex: BibTeX
@article{doi:10.1021/bi048318h,
author = {Huber, Robert and Köhler, Thomas and Lenz, Martin O. and Bamberg, Ernst and Kalmbach, Rolf and Engelhard, Martin and Wachtveitl, Josef},
title = {pH-Dependent Photoisomerization of Retinal in Proteorhodopsin},
journal = {Biochemistry},
volume = {44},
number = {6},
pages = {1800-1806},
year = {2005},
doi = {10.1021/bi048318h},
note ={PMID: 15697205},
URL = {https://doi.org/10.1021/bi048318h},
eprint = {https://doi.org/10.1021/bi048318h},
abstract = {The early steps in the photocycle of the bacterial proton pump proteorhodopsin (PR) were analyzed by ultrafast pump/probe spectroscopy to compare the rate of retinal isomerization at alkaline and acidic pH values. At pH 9, the functionally important primary proton acceptor (Asp97, pKa = 7.7) is negatively charged; consequently, a reaction cycle analogous to the archaeal bacteriorhodopsin (BR) is observed. The excited electronic state of PR displays a pronounced biphasic decay with time constants of 400 fs and 8 ps. At pH 6 where Asp97 is protonated a similar biphasic decay is observed, although it is significantly slower (700 fs and 15 ps). The results indicate, in agreement to similar findings in other retinal proteins, that also in PR the charge distribution within the chromophore binding pocket is a major determinant for the rate and the efficiency of the primary reaction. }
}

2004

Jan Helbing, Harald Bregy, Jens Bredenbeck, Rolf Pfister, Peter Hamm, Robert Huber, Josef Wachtveitl, Luca De Vico, and Massimo Olivucci,
A fast photoswitch for minimally perturbed peptides: investigation of the trans-->cis photoisomerization of N-methylthioacetamide., J. Am. Chem. Soc. , vol. 126, no. 28, pp. 8823-8834, 06 2004.
DOI:10.1021/ja049227a
Bibtex: BibTeX
@Article{HU_2004_Helbing_a,
  Title                    = {{A fast photoswitch for minimally perturbed peptides: investigation of the trans-->cis photoisomerization of N-methylthioacetamide.}},
  Author                   = {Helbing, Jan and Bregy, Harald and Bredenbeck, Jens and Pfister, Rolf and Hamm, Peter and Huber, Robert and Wachtveitl, Josef and {De Vico}, Luca and Olivucci, Massimo},
  Journal                  = {Journal of the American Chemical Society},
  Year                     = {2004},

  Month                    = jul,
  Number                   = {28},
  Pages                    = {8823--34},
  Volume                   = {126},

  Doi                      = {10.1021/ja049227a},
  ISSN                     = {0002-7863},
keywords = {AG-Huber},
  Url                      = {http://pubs.acs.org/doi/abs/10.1021/ja049227a}
}

2003

Robert Huber, Jacques E. Moser, Michael Grätzel, and Josef Wachtveitl,
Beyond vibrationally mediated electron transfer: interfacial charge injection on a sub-10-fs time scale, in Physical Chemistry of Interfaces and Nanomaterials II , Tianquan Lian and Hai-Lung Dai, Eds. International Society for Optics and Photonics, Dec.2003. pp. 121-131.
DOI:10.1117/12.506722
Bibtex: BibTeX
@inproceedings{10.1117/12.506722,
author = {Robert Huber and Jacques E. Moser and Michael Gratzel and Josef L. Wachtveitl},
title = {{Beyond vibrationally mediated electron transfer: interfacial charge injection on a sub-10-fs time scale}},
volume = {5223},
booktitle = {Physical Chemistry of Interfaces and Nanomaterials II},
editor = {Tianquan Lian and Hai-Lung Dai},
organization = {International Society for Optics and Photonics},
publisher = {SPIE},
pages = {121 -- 131},
abstract = {The electron transfer (ET) from organic dye molecules to semiconductor-colloidal systems is characterized by a special energetic situation with a charge transfer reaction from a system of discrete donor levels to a continuum of acceptor states. If these systems show a strong electronic coupling they are amongst the fastest known ET systems with transfer times of less than 10 fs. In the first part a detailed discussion of the direct observation of an ET reaction with a time constant of about 6 fs will be given, with an accompanying argumentation concerning possible artifacts or other interfering signal contributions. In a second part we will try to give a simple picture for the scenario of such superfast ET reactions and one main focus will be the discussion of electronic dephasing and its consequences for the ET reaction. The actual ET process can be understood as a kind of dispersion process of the initially located electron into the colloid representing a real motion of charge density from the alizarin to the colloid.},
keywords = {electron transfer, ultrafast, femtosecond, dye, semiconductor, titanium dioxide},
year = {2003},
doi = {10.1117/12.506722},
URL = {https://doi.org/10.1117/12.506722}
}
Robert Huber, Jacques E. Moser, M. Grutzet, and Josef Wachtveitl,
Beyond vibrationally mediated electron transfer: coherent phenomena in a sub-10-femtosecond reaction regime, 2003 European Quantum Electronics Conference. EQEC 2003 (IEEE Cat No.03TH8665) , pp. 158, 2003.
DOI:10.1109/EQEC.2003.1314015
Bibtex: BibTeX
@INPROCEEDINGS{1314015,
  author={Huber, R. and Moser, J.E. and Grutzet, M. and Wachtveitl, J.},
  booktitle={2003 European Quantum Electronics Conference. EQEC 2003 (IEEE Cat No.03TH8665)}, 
  title={Beyond vibrationally mediated electron transfer: coherent phenomena in a sub-10-femtosecond reaction regime}, 
  year={2003},
  volume={},
  number={},
  pages={158-},
  abstract={This study investigates the systems alizarin as well as coumarin 343 coupled onto TiO/sub 2/ nanoparticles with a femtosecond pump/probe setup. The investigation applies sub 20 fs pump pulses, provided by a noncollinear optical parametric amplifier (NOPA) and a supercontinuum generated in CaF/sub 2/ for a ultrabroadband detection covering a spectral range from 300-960 nm. This work also studies coherent wavepacket propagation succeeding electron transfer at the two systems alizarin/coumarin on TiO/sub 2/. Due to the superfast time scale of the investigated electron transfer (ET) reactions of about 4-7 fs the systems show fundamental differences to conventional molecular ET systems. The ET process is no longer mediated by molecular vibrations and therefore classical molecular ET theories lose their applicability. Results show the real-time coherent excitation of molecular vibrational eigenmodes directly by the ET reaction as well as the generation of phonons during polaron formation in the TiO/sub 2/ lattice. The presented investigations in combination with the classification of the appearing mechanisms could be the basis for an extension of molecular ET theories to superfast systems typically found at molecule/solid state interfaces.},
  keywords={},
  doi={10.1109/EQEC.2003.1314015},
  ISSN={},
  month={June},}

2002

Robert Huber, Jacques E. Moser, Michael Grätzel, and Josef Wachtveitl,
Observation of photoinduced electron transfer in dye/semiconductor colloidal systems with different coupling strengths, Dec.2002. pp. 39-45.
DOI:10.1016/S0301-0104(02)00687-0
Bibtex: BibTeX
@article{HUBER200239,
title = {Observation of photoinduced electron transfer in dye/semiconductor colloidal systems with different coupling strengths},
journal = {Chemical Physics},
volume = {285},
number = {1},
pages = {39-45},
year = {2002},
note = {Unconventional Photoactive Systems},
issn = {0301-0104},
doi = {https://doi.org/10.1016/S0301-0104(02)00687-0},
url = {https://www.sciencedirect.com/science/article/pii/S0301010402006870},
author = {Robert Huber and Jacques E Moser and Michael Grätzel and Josef Wachtveitl},
abstract = {Investigations on the ultrafast electron injection and recombination mechanism from the dyes alizarin and coumarin 343 to wide band gap semiconductor colloids in solution are presented, combined with detailed studies on population, depopulation and relaxation phenomena. We discuss transient absorption measurements on time scales from 100 fs to >1 ns throughout the visible spectral range (350–650 nm), allowing the simultaneous time resolved observation of signals assigned to ground state, cation and injected electron in the conduction band of the semiconductor. Analysis of transient absorption changes in the near UV region, where cation absorption is dominant, allows unambiguous assignment of the various kinetic components. This facilitates the distinction between the different contributions of the various absorbing species also in the congested visible spectral range. Comparison between the two dyes with respect to their different electron transfer parameters provides a direct way to analyze the influence of the electronic coupling element V on the injection and recombination process. Detailed inspection of the decay related spectra for both samples yields information on the environmental response succeeding the cation formation.}
}
Robert Huber,
Elektronentransfer an Farbstoff-Halbleiter-Grenzflächen, Ludwig-Maximilians-Universität München, 06 2002.
File: Huber_Robert.pdf
Bibtex: BibTeX
@PhdThesis{HU_2002_Huber_c,
  Title = {{Elektronentransfer an Farbstoff-Halbleiter-Grenzfl\"{a}chen}},
  Author = {Huber, Robert},
  School = {Ludwig-Maximilians-Universit\"{a}t M\"{u}nchen},
  Year = {2002},
  keywords = {AG-Huber},
  Publisher = {Ludwig-Maximilians-Universit\"{a}t M\"{u}nchen},
  Url = {http://edoc.ub.uni-muenchen.de/93/1/Huber_Robert.pdf}
}
Robert Huber, Jacques E. Moser, Michael Grätzel, and Josef Wachtveitl,
Real-Time Observation of Photoinduced Adiabatic Electron Transfer in Strongly Coupled Dye/Semiconductor Colloidal Systems with a 6 fs Time Constant, J. Phys. Chem. B , vol. 106, no. 25, pp. 6494-6499, 06 2002.
DOI:10.1021/jp0155819
Bibtex: BibTeX
@Article{HU_2002_Huber_a,
  Title                    = {{Real-Time Observation of Photoinduced Adiabatic Electron Transfer in Strongly Coupled Dye/Semiconductor Colloidal Systems with a 6 fs Time Constant}},
  Author                   = {Huber, Robert and Moser, Jacques-E. and Gr\"{a}tzel, Michael and Wachtveitl, Josef},
  Journal                  = {The Journal of Physical Chemistry B},
  Year                     = {2002},

  Month                    = jun,
  Number                   = {25},
  Pages                    = {6494--6499},
  Volume                   = {106},
keywords = {AG-Huber},

  Doi                      = {10.1021/jp0155819},
  ISSN                     = {1520-6106},
  Url                      = {http://pubs.acs.org/doi/abs/10.1021/jp0155819}
}
Robert Huber, Jacques E. Moser, Michael Grätzel, and Josef Wachtveitl,
Photoinduced electron transfer in dye/semiconductor systems on a sub-10-fs time scale - 2002 OSA Technical Digest Series, in The Thirteenth International Conference on Ultrafast Phenomena , Optica Publishing Group, 052002. pp. ThC5.
DOI:10.1364/UP.2002.ThC5
Bibtex: BibTeX
@inproceedings{Huber:02,
author = {Robert Huber and Jacques E. Moser and Michael Gr\"{a}tzel and Josef Wachtveitl},
booktitle = {The Thirteenth International Conference on Ultrafast Phenomena},
journal = {The Thirteenth International Conference on Ultrafast Phenomena},
keywords = {Spectroscopy, surface; Femtosecond phenomena; Molecules; Pump probe spectroscopy; Semiconductors; Solar energy; Temporal resolution; Titanium dioxide},
pages = {ThC5},
publisher = {Optica Publishing Group},
title = {Photoinduced electron transfer in dye/semiconductor systems on a sub-10-fs time scale},
year = {2002},
url = {https://opg.optica.org/abstract.cfm?URI=UP-2002-ThC5},
doi = {10.1364/UP.2002.ThC5},
abstract = {Pump-probe investigation of alizarin adsorbed on the surface of TiO2 colloids reveals a 6 femtosecond electron transfer from the dye molecule to the semiconductor surface, allowing to identify the key factors for this ultrafast electron transfer.},
}

2001

Robert Huber, Helmut Satzger, Wolfgang Zinth, and Josef Wachtveitl,
Noncollinear optical parametric amplifiers with output parameters improved by the application of a white light continuum generated in CaF2, Optics Communications , vol. 194, no. 4, pp. 443-448, 07 2001.
DOI:10.1016/S0030-4018(01)01324-4
Bibtex: BibTeX
@article{HUBER2001443,
title = {Noncollinear optical parametric amplifiers with output parameters improved by the application of a white light continuum generated in CaF2},
journal = {Optics Communications},
volume = {194},
number = {4},
pages = {443-448},
year = {2001},
issn = {0030-4018},
doi = {https://doi.org/10.1016/S0030-4018(01)01324-4},
url = {https://www.sciencedirect.com/science/article/pii/S0030401801013244},
author = {Robert Huber and Helmut Satzger and Wolfgang Zinth and Josef Wachtveitl},
keywords = {Femtosecond pulses, Parametric amplification, White light continuum, Supercontinuum, Frequency conversion, Amplification bandwidth, Calcium fluoride (CaF)},
abstract = {We report the drastic improvement of output parameters of femtosecond noncollinear optical parametric amplifiers by applying supercontinuum seed pulses generated in CaF2 instead of sapphire and imaging via all reflective optics. Features of the setup are broad amplification bandwidths up to 310 THz (470–910 nm), an almost Gaussian beam profile, a divergence with M2 factor of less than 1.4, pulse to pulse energy fluctuations of less than 2.5% and compressibility of the pulses down to 16 fs. The high intensity of the supercontinuum seed pulse (80 nJ) yields a quantum efficiency for the conversion of pump to signal of more than 30%. Even for short wavelengths e.g. at 470 nm pulse energies above 30 μJ were obtained for 110 μJ of 400 nm pump light.}
}

2000

Robert Huber, Sebastian Spörlein, Jacques E. Moser, Michael Grätzel, and Josef Wachtveitl,
The Role of Surface States in the Ultrafast Photoinduced Electron Transfer from Sensitizing Dye Molecules to Semiconductor Colloids, The Journal of Physical Chemistry B , vol. 104, no. 38, pp. 8995-9003, 09 2000. American Chemical Society.
DOI:10.1021/jp9944381
Bibtex: BibTeX
@Article{HU_2000_Huber_a,
  Title                    = {{The Role of Surface States in the Ultrafast Photoinduced Electron Transfer from Sensitizing Dye Molecules to Semiconductor Colloids}},
  Author                   = {Huber, Robert and Sp\"{o}rlein, Sebastian and Moser, Jacques E and Gr\"{a}tzel, Michael and Wachtveitl, Josef},
  Journal                  = {The Journal of Physical Chemistry B},
  Year                     = {2000},

  Month                    = sep,
  Number                   = {38},
  Pages                    = {8995--9003},
  Volume                   = {104},
keywords = {AG-Huber},

  Doi                      = {10.1021/jp9944381},
  ISSN                     = {1520-6106},
  Publisher                = {American Chemical Society},
  Url                      = {http://pubs.acs.org/doi/abs/10.1021/jp9944381}
}
Robert Huber, Sebastian Spörlein, Jacques E. Moser, Michael Grätzel, and Josef Wachtveitl,
Surface States Control Ultrafast Electron Injection in Dye/Semiconductor Colloidal Systems, in Ultrafast Phenomena XII - Proceedings of the 12th International Conference , Springer, 2000. pp. 456--458.
DOI:10.1007/978-3-642-56546-5_133
Bibtex: BibTeX
@InProceedings{10.1007/978-3-642-56546-5_133,
author="Huber, Robert
and Sp{\"o}rlein, Sebastian
and Moser, Jacques E.
and Gr{\"a}tzel, Michael
and Wachtveitl, Josef",
title="Surface States Control Ultrafast Electron Injection in Dye/Semiconductor Colloidal Systems",
booktitle="Ultrafast Phenomena XII",
year="2001",
publisher="Springer Berlin Heidelberg",
address="Berlin, Heidelberg",
pages="456--458",
abstract="Electron injection from photoexcited dye molecules into semiconductor colloidal particles (TiO2 and ZrO2) is investigated by femtosecond (fs) spectroscopy. Ultrafast reaction dynamics in the dye/ZrO2-system with an inaccessible conduction band demonstrates efficient electron transfer to surface defect states.",
isbn="978-3-642-56546-5"
}

1999

Josef Wachtveitl, Robert Huber, Sebastian Spörlein, Jacques E. Moser, and Michael Grätzel,
Ultrafast photoinduced electron transfer in coumarin 343 sensitized TiO2-colloidal solution, International Journal of Photoenergy , vol. 1, no. 3, pp. 153-155, 1999.
DOI:10.1155/S1110662X99000264
Bibtex: BibTeX
@Article{HU_1999_Wachtveitl_a,
  Title                    = {{Ultrafast photoinduced electron transfer in coumarin 343 sensitized TiO2-colloidal solution}},
  Author                   = {Wachtveitl, Josef and Huber, Robert and Sp\"{o}rlein, Sebastian and Moser, Jacques E and Gr\"{a}tzel, Michael},
  Journal                  = {International Journal of Photoenergy},
  Year                     = {1999},
  Number                   = {3},
  Pages                    = {153--155},
  Volume                   = {1},
keywords = {AG-Huber},

  Doi                      = {10.1155/S1110662X99000264},
  ISSN                     = {1110-662X},
  Url                      = {http://www.hindawi.com/journals/ijp/1999/418298/abs/}
}

1998

Robert Huber, Martin Koch, and Jochen Feldmann,
Laser-induced thermal expansion of a scanning tunneling microscope tip measured with an atomic force microscope cantilever, Appl. Phys. Lett. , vol. 73, no. 17, pp. 2521-2523, Oct. 1998.
DOI:10.1063/1.122502
Bibtex: BibTeX
@Article{HU_1998_Huber_b,
  Title                    = {{Laser-induced thermal expansion of a scanning tunneling microscope tip measured with an atomic force microscope cantilever}},
  Author                   = {Huber, R and Koch, M and Feldmann, J},
  Journal                  = {Applied Physics Letters},
  Year                     = {1998},
  Number                   = {17},
  Pages                    = {2521},
  Volume                   = {73},
keywords = {AG-Huber},

  Doi                      = {10.1063/1.122502},
  ISSN                     = {00036951},
  Url                      = {http://scitation.aip.org/content/aip/journal/apl/73/17/10.1063/1.122502}
}
Robert Huber, Martin Koch, M Perner, Wolfgang Spirkl, and Jochen Feldmann,
Time-resolved thermal expansion of an STM tip after ultrafast optical excitation, in Technical Digest. Summaries of Papers Presented at the Conference on Lasers and Electro-Optics. Conference Edition. 1998 Technical Digest Series (IEEE Cat. No.98CH36178) , 1998. pp. 526-527.
DOI:10.1109/CLEO.1998.676586
Bibtex: BibTeX
@INPROCEEDINGS{676586,
  author={Huber, R. and Koch, M. and Perner, M. and Spirkl, W. and Feldmann, J.},
  booktitle={Technical Digest. Summaries of Papers Presented at the Conference on Lasers and Electro-Optics. Conference Edition. 1998 Technical Digest Series, Vol.6 (IEEE Cat. No.98CH36178)}, 
  title={Time-resolved thermal expansion of an STM tip after ultrafast optical excitation}, 
  year={1998},
  volume={},
  number={},
  pages={526-527},
  doi={10.1109/CLEO.1998.676586}}

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