Study on molecular photoionization in femtosecond laser field

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Show simple item record Li, Hui 2013-06-18T19:14:36Z 2013-06-18T19:14:36Z 2013-06-18
dc.description.abstract This thesis consists of two major parts. The first part concerns studies of the orientation dependence of the ionization of diatomic molecules in intense, femtosecond two-color laser fields. The second part is about studies on the ionization mechanisms of the C[subscript]6[subscript]0 molecule in femtosecond near-infrared and ultraviolet laser fields. In the first part, experimental and theoretical results on the asymmetric ion emission of the heteronuclear molecules CO and NO in two-color laser fields are discussed. The two-color fields, which can be tailored by a relative phase, are used to ionize and dissociate CO and NO molecules, both of which are molecules with small polarizabilities. The resulting C[superscript]+, C[superscript]2[superscript]+, N[superscript]+ and O[superscript]+ ions are detected by a velocity map imaging (VMI) setup. The photoelectrons from above-threshold ionization (ATI) of Xe are studied under such a two-color field to assign the phase. For both CO and NO we find that enhanced ionization occurs when the molecule is oriented with the electric field pointing from the C or N atom toward the O atom. This is in agreement with the molecular orbital Ammosov-Delone-Krainov (MO-ADK) theory and the Stark-corrected strong-field-approximation (SFA) calculations. The second part is devoted to the investigation of the ionization mechanism of neutral C[subscript]6[subscript]0 molecules with 30 fs laser pulses at about 800 nm and with 50 fs pulses at about 400 nm. The angular distributions of photoelectrons are measured utilizing VMI. Measurements under different intensities are carried out for the two wavelengths. In our work, thermal electron emission is highly suppressed by the use of short pulses. For near-infrared excitation, photoelectron angular distributions (PADs) that contain six lobes are observed for low energy electrons. This behavior is different from studies for longer pulses of about 120 fs [1]. Further analysis indicates that the PADs might originate from single photon ionization of a super atomic molecular orbital (SAMO), however, a detailed assignment requires further theoretical work. The PADs for the ultraviolet excitation show very similar structures to earlier results [1]. For the near-infrared excitation, we have carried out studies as a function of the chirp of the pulses and find effects on photoelectron spectra and on PADs, which are tentatively explained by sequential multiphoton ionization via “doorway” states. en_US
dc.language.iso en_US en_US
dc.publisher Kansas State University en
dc.subject Molecular photoionization en_US
dc.subject Two-color femtosecond laser field en_US
dc.subject Chirp dependence en_US
dc.subject Fullerene en_US
dc.title Study on molecular photoionization in femtosecond laser field en_US
dc.type Thesis en_US Master of Science en_US
dc.description.level Masters en_US
dc.description.department Department of Physics en_US
dc.description.advisor Matthias Kling en_US
dc.subject.umi Atomic Physics (0748) en_US 2013 en_US August en_US

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