Laser and X-ray Physics

Technical University of Munich

Department of Physics

James-Franck-Str. 1

85748 Garching

Tel. +49 89 289 12840


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Research focus: attosecond physics, ultrafast quantum dynamics, laser spectroscopy

Our group's activities aim at investigating processes inside atoms, molecules and solids on the shortest timescale reached so far, the attosecond timescale. New insight into ever smaller microscopic units of matter as well as in ever faster evolving chemical, physical or atomic processes pushes the frontiers in many fields in science. The interest in these ultrashort processes is the driving force behind the development of sources and measurement techniques that allow time-resolved studies at ever shorter timescales.

Ultrafast laser spectroscopy of quantum dynamics

Pump-probe experiments turned out to be the most direct approach to time-domain investigations of fast-evolving microscopic processes: A short excitation pulse sets the process going and a probe pulse takes snapshots of subsequent stages of its evolution. Accessing atomic and molecular inner-shell processes directly in the time-domain has until recently been frustrated by the required combination of short wavelengths and sub-femtosecond pulse duration. A solution of this problem, namely the concept of light-field-controlled XUV photoemission allows to substitute either the XUV pump or the XUV probe pulse by a strong few-cycle laser field, in other words, to employ the XUV pulse as a pump and the light pulse as a probe or vice versa. The basic prerequisite, namely the generation and measurement of isolated sub-femtosecond XUV pulses synchronized to a strong few-cycle light pulse with attosecond precision, opened up a route to time-resolved inner-shell atomic as well as molecular spectroscopy with present day sources [1,2].

In general, the experimental tools used in the group are pump/probe techniques in various constellations (e.g. 2-color) measured with time resolved spectroscopic tools (absorption spectroscopy, photoelectron and ion spectroscopy). Many different sources are being used and developed ranging from the infrared (optical parametric amplification techniques, OPA) to visible (chirped pulse amplification techniques, CPA) [3], ultraviolet (nonlinear optics, NLO), extreme ultraviolet (high-order harmonic generation, HHG) [1,2] to x-rays (free electron lasers, FEL) [4].

The goal of this research group is to use femtosecond and attosecond technology and methods to resolve ultrafast processes in condensed matter sciences by providing direct access to the motion of electrons in molecular and solid state systems.

Efforts are undertaken to control and measure the attosecond-scale charge hopping that takes place by the movement of bound electrons between the nuclei of simple molecules. In these complex systems a charge transfer may solely be driven by electron correlation.

Of special interest are electronic transport and bandstructure effects in solids [5-7] and nanostructured systems [8], electronic correlation [9] and dephasing.

The research is conducted at the chair of Laser and X-Ray Physics (E11) at the Physics Department of TUM, at the Max-Planck-Insitute of Quantum Optics (Max-Planck-Fellow) and at beamtimes at large scale facilities (eg. LCLS at Stanford Linear Accelerator Center).

Selected publications

1. R. Kienberger et al., Science, 297 (2002)
2. R. Kienberger, et al., Nature, 427(2004)
3. T. Wittmann et al., Nature Physics 5 (2009)
4. W. Helml et al., Nature Photonics 8 (2014)
5. A. Schiffrin et al., Nature 507 (2014)
6. Sommer et al., Nature 534 (2016)
7. M.S. Wagner, et al., Phys. Chem. Chem. Phys. 17 (2015)
8. S. Neppl et al., Nature 517 (2015)
9. M. Ossiander et al., Nature Physics 13 (2016)


Ultrafast hot-carrier relaxation in silicon monitored by phase-resolved transient absorption spectroscopy

M. Wörle, A.W. Holleitner, R. Kienberger, H. Iglev

Physical Review B 104, L041201 (2021).

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The relaxation dynamics of hot carriers in silicon (100) is studied via a holistic approach based on phase-resolved transient absorption spectroscopy with few-cycle optical pulses. After excitation by a sub-5-fs light pulse, strong electron-electron coupling leads to an ultrafast single electron momentum relaxation time of 10 fs. The thermalization of the hot carriers is visible in the temporal evolution of the effective mass and the collision time as extracted from the Drude model. The optical effective mass decreases from 0.3m(e) to about 0.125m(e) with a time constants of 58 fs, while the collision time increases from 3 fs for the shortest timescales with a saturation at approximately 18 fs with a time constant of 150 fs. The observation shows that both Drude parameters exhibit different dependences on the carrier temperature. The presented information on the electron mass dynamics as well as the momentum-, and electron-phonon scattering times with unprecedented time resolution is important for all hot-carrier optoelectronic devices.

DOI: 10.1103/PhysRevB.104.L041201

Toward femtosecond electronics up to 10 THz

N. Fernandez, P. Zimmermann, P. Zechmann, M. Worle, R. Kienberger, A.W. Holleitner

Ultrafast Phenomena and Nanophotonics XXIII 10916, 109160R (2019).

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We numerically compute the effective diffraction index and attenuation of coplanar stripline circuits with microscale lateral dimensions on various substrates including sapphire, GaN, silica glass, and diamond grown by chemical vapor deposition. We show how to include dielectric, radiative and ohmic losses to describe the pulse propagation in the striplines to allow femtosecond on-chip electronics with frequency components up to 10 THz.

DOI: 10.1117/12.2511668

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