Tim Laarmann - Academia.edu (original) (raw)
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Papers by Tim Laarmann
The basic idea is to implement Thomson scattering with free electron laser (FEL) radiation at nea... more The basic idea is to implement Thomson scattering with free electron laser (FEL) radiation at near-solid density plasmas as a diagnostic method which allows the determination of plasma temperatures and densities in the warm dense matter (WDM) regime (free electron density of n{sub e} = 10²¹-10² cm³ with temperatures of several eV). The WDM regime [1] at near-solid density (n{sub
Applied Physics Letters, 2014
New Journal of Physics, 2009
Kinetic Boltzmann equations are used to describe electron emission spectra obtained after irradia... more Kinetic Boltzmann equations are used to describe electron emission spectra obtained after irradiation of noble-gas clusters with intense vacuum ultraviolet (VUV) radiation from a free-electron-laser (FEL). The experimental photoelectron spectra give a complementary and more detailed view of nonlinear processes within atoms and clusters in an intense laser field compared to mass spectroscopy data. Results from our model obtained in this study confirm the experimental and theoretical findings on the differing ionization scenarios at longer (100 nm) and shorter (32 nm) VUV radiation wavelengths. At the wavelength of 100 nm the thermoelectronic electron emission dominates the emission spectra. This indicates the plasma formation and the inverse bremsstrahlung (IB) heating of electrons inside the plasma. This effect is clearly visible for xenon (with the fitted temperature of 6-7 eV), and less visible for argon (with the fitted temperature of 2-3 eV). The two-photon-ionization rate for argon that initiates the cluster ionization, is much lower than the singlephotoionization rate for xenon. Also, more of the photoelectrons created within an argon cluster are able to leave it, as they are more energetic than those released from a xenon cluster. Therefore, the IB heating of plasma electrons in argon is
Springer Series in Chemical Physics, 2008
ABSTRACT Recent progress in the understanding of the primary excitation mechanisms of the C60 ful... more ABSTRACT Recent progress in the understanding of the primary excitation mechanisms of the C60 fullerene in intense laser pulses is reported. By analyzing mass spectra as a function of pulse duration, laser intensity and time delay between pump- and probe pulse insight into fundamental photoinduced processes such as ionization and fragmentation is obtained. Using ultrashort sub-10fs pulses excitation times are addressed which lie well below the characteristic time scales for electron–electron and electron–phonon coupling. The measured saturation intensities of multiply charged parent ions indicate that for higher charge states the well known C60 giant plasmon resonance is involved in creating ions and a significant amount of large fragments through a non-adiabatic multi-electron dynamics. To enhance the formation of large fragments femtosecond laser pulses tailored with closed-loop, optimal control feedback were used. A characteristic pulse sequence excites oscillations in C60 with large amplitude by coherent heating of nuclear motion. Again, the experimental findings can be understood by a laser-induced multi-electron excitation via the electronically excited resonance followed by efficient coupling to the radial symmetric breathing vibration of C60.
International Journal of Optics, 2011
The femtosecond nature of X-ray free electron laser (FEL) pulses opens up exciting research possi... more The femtosecond nature of X-ray free electron laser (FEL) pulses opens up exciting research possibilities in time-resolved studies including femtosecond photoemission and diffraction. The recent developments of seeding X-ray FELs extend their capabilities by creating stable, temporally coherent, and repeatable pulses. This in turn opens the possibility of spectral engineering soft Xray pulses to use as a probe for the control of quantum dynamics. We propose a method for extending coherent control pulseshaping techniques to the soft X-ray spectral range by using a reflective geometry 4f pulse shaper. This method is based on recent developments in asymmetrically cut multilayer optic technology and piezoelectric substrates.
Advances In Atomic, Molecular, and Optical Physics, 2005
Free electron lasers (FEL) for generating intense vacuum ultra violet (VUV) or x-ray radiation wi... more Free electron lasers (FEL) for generating intense vacuum ultra violet (VUV) or x-ray radiation will become available in the near future. Experiments for the basic understanding of atomic physics are an important early task, since all applications of radiation from short-wavelength FELs ...
The basic idea is to implement Thomson scattering with free electron laser (FEL) radiation at nea... more The basic idea is to implement Thomson scattering with free electron laser (FEL) radiation at near-solid density plasmas as a diagnostic method which allows the determination of plasma temperatures and densities in the warm dense matter (WDM) regime (free electron density of n{sub e} = 10²¹-10² cm³ with temperatures of several eV). The WDM regime [1] at near-solid density (n{sub
Applied Physics Letters, 2014
New Journal of Physics, 2009
Kinetic Boltzmann equations are used to describe electron emission spectra obtained after irradia... more Kinetic Boltzmann equations are used to describe electron emission spectra obtained after irradiation of noble-gas clusters with intense vacuum ultraviolet (VUV) radiation from a free-electron-laser (FEL). The experimental photoelectron spectra give a complementary and more detailed view of nonlinear processes within atoms and clusters in an intense laser field compared to mass spectroscopy data. Results from our model obtained in this study confirm the experimental and theoretical findings on the differing ionization scenarios at longer (100 nm) and shorter (32 nm) VUV radiation wavelengths. At the wavelength of 100 nm the thermoelectronic electron emission dominates the emission spectra. This indicates the plasma formation and the inverse bremsstrahlung (IB) heating of electrons inside the plasma. This effect is clearly visible for xenon (with the fitted temperature of 6-7 eV), and less visible for argon (with the fitted temperature of 2-3 eV). The two-photon-ionization rate for argon that initiates the cluster ionization, is much lower than the singlephotoionization rate for xenon. Also, more of the photoelectrons created within an argon cluster are able to leave it, as they are more energetic than those released from a xenon cluster. Therefore, the IB heating of plasma electrons in argon is
Springer Series in Chemical Physics, 2008
ABSTRACT Recent progress in the understanding of the primary excitation mechanisms of the C60 ful... more ABSTRACT Recent progress in the understanding of the primary excitation mechanisms of the C60 fullerene in intense laser pulses is reported. By analyzing mass spectra as a function of pulse duration, laser intensity and time delay between pump- and probe pulse insight into fundamental photoinduced processes such as ionization and fragmentation is obtained. Using ultrashort sub-10fs pulses excitation times are addressed which lie well below the characteristic time scales for electron–electron and electron–phonon coupling. The measured saturation intensities of multiply charged parent ions indicate that for higher charge states the well known C60 giant plasmon resonance is involved in creating ions and a significant amount of large fragments through a non-adiabatic multi-electron dynamics. To enhance the formation of large fragments femtosecond laser pulses tailored with closed-loop, optimal control feedback were used. A characteristic pulse sequence excites oscillations in C60 with large amplitude by coherent heating of nuclear motion. Again, the experimental findings can be understood by a laser-induced multi-electron excitation via the electronically excited resonance followed by efficient coupling to the radial symmetric breathing vibration of C60.
International Journal of Optics, 2011
The femtosecond nature of X-ray free electron laser (FEL) pulses opens up exciting research possi... more The femtosecond nature of X-ray free electron laser (FEL) pulses opens up exciting research possibilities in time-resolved studies including femtosecond photoemission and diffraction. The recent developments of seeding X-ray FELs extend their capabilities by creating stable, temporally coherent, and repeatable pulses. This in turn opens the possibility of spectral engineering soft Xray pulses to use as a probe for the control of quantum dynamics. We propose a method for extending coherent control pulseshaping techniques to the soft X-ray spectral range by using a reflective geometry 4f pulse shaper. This method is based on recent developments in asymmetrically cut multilayer optic technology and piezoelectric substrates.
Advances In Atomic, Molecular, and Optical Physics, 2005
Free electron lasers (FEL) for generating intense vacuum ultra violet (VUV) or x-ray radiation wi... more Free electron lasers (FEL) for generating intense vacuum ultra violet (VUV) or x-ray radiation will become available in the near future. Experiments for the basic understanding of atomic physics are an important early task, since all applications of radiation from short-wavelength FELs ...