【1】15：00～16：00
講演者： Professor Eckart Ruehl (Freie Universitaet Berlin)
題目："Molecules, clusters, and free nanoparticles studied by short pulse and short wavelength radiation"
【2】16：00～17：00
講演者：Dr. Heide Ibrahim (Photo-Molecular Science II, IMS)
題目："Tracing, amplifying, and steering chromophore- bath coherences by ultrashort pulse trains"
概 要 【講演1】
Short pulse and short wavelength radiation is a selective probe to study structural and dynamic properties of isolated molecules, size-selected clusters, and free nanoparticles as nanoscopic building blocks of matter and possible nanomaterials. Radiation from SASE free electron lasers (FEL), femtosecond laser sources, as well as synchrotron radiation are used for this work. The following aspects are discussed:
1) Shaped and chirped femtosecond laser pulses permit to tune and optimize the relaxation and fragmentation dynamics of molecules.
2) Photoemission from shallow core levels of size-selected metal clusters by FEL-radiation is a unique way to use core-hole screening as a probe for the metal-to-insulator transition in free clusters.
3) FEL-radiation is also used to study the photoemission from free nanoparticles in a beam by velocity map imaging (VMI). Complimentary results are derived from the use of 85 fs laser pulses from a 804 nm Ti-sapphire laser as well as monochromatic synchrotron radiation. This yields size effects in the emission of low kinetic energy electrons from nanoscopic particles. Dynamical information on the photoemission process is studied via femtosecond pump-probe experiments.
4) Alternatively, charging of trapped single nanoparticles is studied by synchrotron radiation, where structured nanoparticles of core-shell architecture provide distinct information on the electron emission mechanisms.
5) Finally, results on the interaction of nanoparticles with biological matter probed by X-ray microscopy will be presented.
【講演2】
Excitation with phase controlled pulse trains allows for a merging of the spectroscopic opponents temporal and energetic selectivity. With a train of 5 phase controlled ultrashort pulses a weak coherent mode is enhanced to exceed a dominant incoherent background. The model system investigated is the halogen Br2 embedded in an Ar matrix -the applied scheme however is very general. Wave packet interference in the chromophore generates a spectral comb which is adjusted to a progression of internal Br2 vibrations (zero phonon lines) or modes strongly coupled to phonons of the surrounding Ar lattice (phonon side bands). Excitations involving several 100 degrees of freedom remain coherent on a picosecond timescale and resist propagation and mode scrambling. The trains are generated by a straightforward programming of the spectral comb in a pulse shaper unit, which inherently steers the mode specific phase evolution of the system. In the current experiment, with those trains furthermore matrix induces predissociation was controlled.
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