Transiente Absorptions- und Dispersionsspektroskopie im fernen Ultraviolett mit ultrakurzen Pulsen

Abstract

Ultrashort pulses, i. e. pulses with few cycles, which span the visible to infrared (VIS-IR) or extreme ultraviolet spectral range, are widely used tools in strong field and attosecond physics. Such pulses are also required in the deep and vacuum ultraviolet spectral range for time-resolved spectroscopy. However, their generation and successful application has hardly been reported so far. The reason for this is the strong dispersion and absorption of all materials, which in turn makes this spectral range interesting for spectroscopy. Difficulties arise in spectral or spatial separation of harmonics from the generating pulses and subsequent transport to the position of the sample. Suitable optics, such as filters and polarizers are hardly available on the market, expensive and associated with experimental drawbacks. In this PhD thesis, the close-to-collinear beam geometry is investigated in detail using wide-bandgap dielectrics as samples. By superimposing two VIS-IR pulses, a multifaceted structure of temporal and spatial harmonics is created, which allows the generation and separation of pulses in the deep ultraviolet (DUV) without having to rely on spectral filters or polarizers. Surprisingly, the third harmonic consists of double pulses. A new method for the generation of ultrashort pulses by harmonic concatenation is introduced. DUV pulses with a duration of 1.5 fs are synthesized. A new technique is developed for the temporal characterization of the weak broadband DUV pulses, which is based on delay scans of the cross-phase modulation with intense VIS-IR pulses. The DUV pulses are used in a new, further developed variant of transient absorption spectroscopy, called transient absorption and dispersion spectroscopy (TADS), in which double pulses are used as probe pulses. For example, a 250 nm thick, free-standing diamond membrane with a band gap in the DUV is used as a sample. The experiments and their interpretations are supported by computer simulations in the form of nonlinear pulse propagation.