Thesis : David STAEDTER (LCAR), september 2013

Femtosecond time-resolved spectroscopy in polyatomic systems investigated by velocity-map imaging and high-order harmonic generation

=> La thèse en texte intégral

Abstract : Revealing the underlying ultrafast dynamics in molecular reaction spectroscopy demands state-of-art imaging techniques to follow a molecular process step by step . Femtosecond time-resolved velocity-map imaging is used to study the photodissociation dynamics of chlorine azide (ClN3). Here especially the co-fragments chlorine and N3 are studied on the femtosecond timescale in two excitation energy regions around 4.67 eV and 6.12 eV, leading to the formation of a linear N3 fragment and a cyclic N3 fragment, respectively. This work is the first femtosecond spectroscopy study revealing the formation of cyclic N3. The second part of the talk is based on the generation and application of XUV light pulses by high-order harmonic generation with an intense femtosecond laser pulse in a molecular target. A phase sensitive attosecond spectroscopy experiments was conducted to study vibrational dynamics of SF6 : high-order harmonic interferometry using two intense XUV probe pulses. The temporal dependencies in phase and amplitude reveal the vibrational dynamics in SF6 and demonstrate that high-order harmonic generation is sensitive to the internal excitations. Last but not least, the use of high-order harmonics as a XUV photon source for the velocity-map imaging spectrometer is investigated. Using time-resolved photoelectron imaging, the relaxation dynamics initiated with 9.3 eV in acetylene are investigated.

rechercher sur site