1,721,103 research outputs found
Entwicklung und Inbetriebnahme eines Pulseformers für extrem ultraviolette und weiche Röntgenstrahlen
No full textIn the course of the present experimental PhD work the first extreme ultraviolet (XUV) and soft x-ray pulse shaper relying on reflective optics has been developed. Its use will allow arbitrary control on the time-frequency spectrum of femtosecond pulses generated by seeded free-electron lasers (FEL) and high-harmonic generation (HHG) sources.
The device is based on the geometry of a 4f grating compressor. It has been applied to shorter wavelengths through the use of grazing incidence optics operated under ultra-high vacuum conditions. The design blaze angle and line density of the gratings allow the manipulation of all the different harmonics typical of high-gain harmonic generation (HGHG) and echo-enabled harmonic generation (EEHG) FELs, as well as of HHG sources, without the need of realignment of the instrument and even simultaneously in multi-color experiments.
Furthermore, the diagnostics necessary for commissioning of the pulse shaper have been realized, including an UV-IR cross-correlator for initial studies using 266nm femtosecond pulses. HGHG seeding at FLASH and temporal characterization of the amplified XUV and soft x-rays by means of THz streaking has been achieved with important contributions by the author of this thesis. These longitudinally fully coherent FEL pulses are well-suited for future shaping applications.
A successful proof-of-principle pulse shaping experiment using 266nm light has been performed, demonstrating spectral phase-control on femtosecond UV pulses.Im Zuge der vorliegenden experimentellen Doktorarbeit wurde der erste Pulsformer für extrem ultraviolette (XUV) und weiche Röntgenstrahlen entwickelt, der ausschließlich auf reflektierende Optik setzt. Seine Nutzung wird die beliebige Steuerung des Zeit-Frequenz-Spektrums der Femtosekundenpulse ermöglichen, die von seeded Freie-Elektronen-Lasern (FEL) und Hohe-Harmonischen Quellen (high harmonic generation, HHG) generiert werden.
Das Gerät basiert auf der Geometrie eines 4f Gitterkompressors. Der Einsatz für kürzere Wellenlängen wird durch die Verwendung von Optiken unter streifendem Einfall im Ultrahochvakuum ermöglicht. Die Blazewinkel und Liniendichte der Gitter wurden so ausgewählt, dass die Manipulation aller verschiedenen Harmonischen für high-gain harmonic generation (HGHG) und echo-enabled harmonic generation (EEHG) FELs sowie für HHG Quellen ermöglicht wird, ohne eine Neujustage des Instruments zu erfordern, und erlaubt sogar die gleichzeitige Nutzung mehrerer Harmonischer in Mehrfarben-Experimenten.
Ferner wurden Diagnosegeräte entworfen, die für die Inbetriebnahme des Pulsformers nötig sind, inklusive eines UV-IR Cross-Korrelators für die ersten Versuchen mit 266nm Femtosekundenpulsen.
HGHG Seeding bei FLASH und die zeitliche Charakterisierung der verstärkten XUV- und weichen Röntgenstrahlen mittels THz Streaking wurde mit wichtigen Beiträgen des Autors dieser Doktorarbeit erreicht. Diese longitudinal vollständig kohärenten FEL-Impulse sind für zukünftige Experimente mit geformten Pulsen gut geeignet.
Ein Nachweis der Funktionalität des Pulsformers wurde unter Nutzung von 266nm Licht erfolgreich erbracht, indem die spektrale Phasensteuerung an Femtosekunden-UV-Pulsen demonstriertet wurde
High-power Few-cycle MID-IR Pulse Generation for Vibrational Spectroscopy
No full textHigh-power, high-energy, ultrashort, mid-infrared (MID-IR) laser systems operating at high repetition rates are of significant interest for coherent vibrational spectroscopy investigations within the "fingerprint region'' (6-16 um). First of all, the optical properties of Li-based nonlinear crystals (NLC) for MID-IR generation are evaluated under high power laser irradiation at 1030\,nm central wavelength using a thermal imaging method. It turns out that lithium gallium sulfide (LGS) crystal exhibits a relatively low linear absorption coefficient < 0.002 cm^{-1}, the lowest nonlinear absorption coefficient < 3.2 x 10^{-4} cm/W and a nonlinear refractive index < 6.4 x 10^{-15} cm^{2}/W, positioning it as a highly promising material candidate for MID-IR optical parametric chirped-pulse amplifier (OPCPA) applications.
Based on the LGS crystal, a versatile design of a MID-IR OPCPA laser system is developed, featuring two complementary operation modes differ that in the group-delay dispersion (GDD) of the signal pulse. One scheme provides a wavelength-tunable source (from 4.2 to 11 um) at ~ 1 ps pulse width, while the other scheme generates a broadband pulse (from 7 to 11 um) centered at 9 um with 114 fs pulse duration, which corresponds to about 3 optical cycles. Both MID-IR laser operation modes exhibit high average power exceeding 200 mW and high pulse energy of 1.2 uJ operating at 200 kHz, having significant potential for vibrational spectroscopy and microscopy making use of characteristic molecular fingerprints in the MID-IR spectral range.
Moreover, by utilizing the broadband ultrashort MID-IR pulse, the ultra-broadband vibrational sum-frequency generation (BB-VSFG) spectroscopy is demonstrated using glucose pellets as a proof-of-principle sample, revealing 8 characteristic vibrational modes spanning from 800 to 1400 cm^{-1}. Notably, the carbon-oxygen bond stretching mode at 1035 cm^{-1} shows high sensitivity to biologically relevant 10 mM of glucose solution in the VSFG spectra. Consequently, this methodology holds promise for blood sugar monitoring in diabetic individuals
Generation and control of ultrafast 10µm laser pulses for driving chemical dynamics
No full textPulsed femtosecond (“ultrafast”) lasers are a trending tool with a vast variety of applications in science and engineering. The current trend towards more and more powerful pulsed lasers in the mid- and far-infrared spectral range enables application of established techniques, like multidimensional spectroscopy and quantum control approaches in these wavelength regimes. These efforts will produce new insights in dynamics of couplings on the atomic level and allow for a better understanding of reaction pathways of catalytic processes in material science or in the life sciences. This work presents the development of a source for light-phase ("CEP") stable femtosecond pulses in the mid-infrared spectral range. The wavelength of the pulses is tunable between 7 and 15 µm. The pulses are shaped in the time domain by deliberately delaying and/or attenuating frequency components in the spectral domain. The result is arbitrary control of the frequency distribution within these ultrashort pulses paving the way towards experiments of highly complex control over molecular vibrational excitations even in the electronic ground state
Helium droplets in intense laser fields studied with XUV fluorescence spectroscopy
No full textIn this work, XUV fluorescence spectroscopy was used to study energy absorption and dissipation in laser-driven helium nanoplasms interacting with intense infrared laser pulses. In contrast to typical plasmas of atomic helium, the cluster environment allows energetic de-excitation by means of three-body recombination in the nanoplasma. The amount of three-body recombination increases the better the conditions for resonant heating of the nanoplasma are met. This was measured for clusters and large helium droplets with an average size between 1.2 × 10 atoms and 1.6 × 10 atoms. Using the largest clusters with an average size above 2.6 × 10 atoms and 180 fs long pulses, an extremely broadband XUV cluster continuum spectrum is observed for the first time. The novel continuum spectrum ranges from a photon energy of 21 eV to 70 eV, although these figures are limited by the maximum wavelength sensitivity of the spectrometer used. Using much shorter pulses at a central wavelength of 2060 nm with a pulse duration of only 50 fs, this continuum spectrum already appears in much smaller clusters starting at an average size of 7.5 × 10 atoms. The hypothesis is that the continuum is generated on a time scale shorter than the pulse length of the driving laser and thus within a relatively intact cluster
XUV Fluoreszenzspektroskopische Untersuchung von Helium Tröpfchen in intensiven Laserlicht
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Interferometry on small quantum systems at short wavelength
No full textThe present work concentrates on prototypical studies of light-induced correlated manybodydynamics in complex systems. In its course a reflective split-and-delay unit (SDU)for phase-resolved one-color pump-probe experiments with gas phase samples using VUV–XUV laser pulses was built. The collinear propagation of pump and probe pulses is ensuredby the special geometry of the SDU and allows to perform phase-resolved (coherent)autocorrelation measurements. The control of the pump-probe delay with attosecondprecision is established by a specially developed diagnostic tool based on an in-vacuumwhite light interferometer that allows to monitor the relative displacement of the SDU reflectorswith nanometer resolution. Phase-resolved (interferometric) pump-probe experimentswith developed SDU require spatially-resolved imaging of the ionization volume.For this an electron–ion coincidence spectrometer was built. The spectrometer enablescoincident detection of photoionization products using velocity map imaging (VMI) techniquefor electrons and VMI or spatial imaging for ions. In first experiments using thedeveloped SDU and the spectrometer in the ion spatial-imaging mode linear field autocorrelationof free-electron laser pulses at the central wavelength of 38 nm was recorded.A further focus of the work were energy- and time-resolved resonant two-photonionization experiments using short tunable UV laser pulses on C60 fullerene. The experimentsdemonstrated that dipole-selective excitation on a timescale faster than thecharacteristic intramolecular energy dissipation limits the number of accessible excitationpathways and thus results in a narrow resonance. Time-dependent one-color pumpprobestudy showed that nonadiabatic (vibron) coupling is the dominant energy dissipationmechanism for high-lying electronic excited states in C60
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