7 research outputs found
Atmospheric photochemical loss of H and H2 from formaldehyde:the relevance of ultrafast processes
Tuning and Tracking of Coherent Shear Waves in Molecular Films
We have determined the time-dependent
displacement fields in molecular sub-micrometer thin films as response
to femtosecond and picosecond laser pulse heating by time-resolved
X-ray diffraction. This method allows a direct absolute determination
of the molecular displacements induced by electron–phonon interactions,
which are crucial for, for example, charge transport in organic electronic
devices. We demonstrate that two different modes of coherent shear
motion can be photoexcited in a thin film of organic molecules by
careful tuning of the laser penetration depth relative to the thickness
of the film. The measured response of the organic film to impulse
heating is explained by a thermoelastic model and reveals the spatially
resolved displacement in the film. Thereby, information about the
profile of the energy deposition in the film as well as about the
mechanical interaction with the substrate material is obtained
Peculiarities of second harmonic generation with chirped femtosecond pulses at high conversion efficiency
Frequency doubling of an infrared laser radiation in non-linear optical crystals is a widely used technique to obtain light in the visible range. The second harmonic generation process is influenced by several well-known parameters. In this article we study the effect of group delay dispersion on the second harmonic generation process for femtosecond pulses. We show, both through simulation and experiments, that for certain parameters even a small amount of chirp can have a detrimental effect on the conversion efficiency as well as the second harmonic beam quality. We also check the effect of higher order dispersion. By properly accounting for those effects the crystal length and focusing conditions can be optimized to reach high conversion efficiency, while maintaining low sensitivity to chirp variations and good beam quality