This presentation was first delivered at Photonics West 2020 on 3 February 2020 and has been included as part of this Digital Forum to enable scholarly dialogue. Please use the original citation when citing:
Proceedings Volume 11278, Ultrafast Phenomena and Nanophotonics XXIV; 112780O (2020) https://doi.org/10.1117/12.2543969
In semiconductors and semimetals, strong THz electric fields can induce a controlled coherent motion of the electrons in the conduction band, via ballistic excitation. In the first picoseconds after THz excitation, the nonlinearities induced by this coherent excitation prevail before more incoherent high field effects start dominating the nonlinear response. Disentangling these different nonlinear contributions with 2D THz spectroscopy, we follow the trajectory of the out-of-equilibrium electron population in low-bandgap semiconductor InSb and. We then extract information on the conduction band curvature and evaluate its anharmonicity and its anisotropy, close to the Gamma-point.
In semiconductors and semimetals, strong THz electric fields can induce a controlled coherent motion of the electrons in the conduction band, via ballistic excitation. In the first picoseconds after THz excitation, the nonlinearities induced by this coherent excitation prevail before more incoherent high field effects start dominating the nonlinear response. Disentangling these different nonlinear contributions with 2D THz spectroscopy, we follow the trajectory of the out-of-equilibrium electron population in low-bandgap semiconductor InSb and. We then extract information on the conduction band curvature and evaluate its anharmonicity and its anisotropy, close to the Gamma-point.
Powerful free electron lasers (FELs) operating in the soft X-ray regime are offering new possibilities for creating
and probing materials under extreme conditions. We describe here simulations to model the interaction of a
focused FEL pulse with metallic solids (niobium, vanadium, and their deuterides) at 13.5 nm wavelength (92 eV)
with peak intensities between 1015 to 1018 W/cm2 and a fixed pulse length of 15 femtoseconds (full width at half
maximum). The interaction of the pulse with the metallic solids was modeled with a non-local thermodynamic
equilibrium code that included radiation transfer. The calculations also made use of a self-similar isothermal fluid
model for plasma expansion into vacuum. We find that the time-evolution of the simulated critical charge density
in the sample results in a critical depth that approaches the observed crater depths in an earlier experiment
performed at the FLASH free electron laser in Hamburg. The results show saturation in the ablation process
at intensities exceeding 1016 W/cm2. Furthermore, protons and deuterons with kinetic energies of several keV
have been measured, and these concur with predictions from the plasma expansion model. The results indicate
that the temperature of the plasma reached almost 5 million K after the pulse has passed.
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