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Softmode excitations in aspirin are studied with two-dimensional terahertz spectroscopy. The coupling of CH3 rotational modes and collective excitations of π electrons results in a nonperturbative nonlinear response induced by moderate THz fields.
Femtosecond pump-probe experiments demonstrate a strong amplification of optically generated coherent phonons by interaction with an intra-miniband current in a biased semiconductor superlattice. Electron-phonon coupling predominantly occurs via the acoustic deformation potential.
Relaxation processes of holes in p-type Ge and GaAs are investigated with picosecond infrared pulses in the wavelength range from 0.8 to 12 μm. The transient inter-valence band absorption of Ge studied in spectrally and temporally resolved measurements reveals subpicosecond carrier-carrier and inter-valence band scattering of the excited holes, followed by the picosecond cooling of hot heavy holes...
Using fully phase-resolved two-dimensional terahertz spectroscopy we study coherent intersubband Rabi oscillations in GaAs quantum wells. A strong terahertz field modifies particularly the phase of the nonlinearly emitted field during the Rabi oscillation.
Powerful 90 fs pulses at a midinfrared wavelength of λ = 3.9 µm drive a femtosecond hard x-ray source (Cu Kα: ℏω = 8.05 keV). Up to 108 X-ray photons/pulse are generated which is twice as many as with 800 nm drivers of a 100 times higher peak intensity.
We study the nonlinear terahertz response of LiNbO3 using 2D spectroscopy. Dissecting the nonlinear response into different orders in the electric field shows a strong shift current Re[J(ν ∼ 0)] ≠ 0 and higher harmonics of the THz fundamental.
We report the first observation of terahertz higher harmonics in graphene by mapping the nonlinear response with broadband electrooptic sampling. The nonlinear response in the non-perturbative regime is determined by intra- and interband electron motions.
The first femtosecond x-ray diffraction experiments on LiBH4 are reported. Off-resonant excitation with 800-nm pulses induces a purely electronic modification of the transient diffraction pattern, followed by coherent atomic motions.
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