48 research outputs found
Plasmonic enhancement of High Harmonic Generation revisited: Predominance of Atomic Line Emission
No full textWe demonstrate nanostructure-enhanced extreme ultraviolet fluorescence from noble gases driven by low-energy, few-cycle light pulses. Despite sufficient local intensities, plasmon-enhanced high harmonic generation is not observed, which follows from the small, nanometer-size coherent source volume
Extreme-ultraviolet light generation in plasmonic nanostructures
No full textStrong-field phenomena in optical nanostructures have enabled the integration of nanophotonics, plasmonics and attosecond spectroscopy. For example, tremendous excitement was sparked by reports of nanostructure-enhanced high-harmonic generation. However, there is growing tension between the great promise held by extreme-ultraviolet and attosecond-pulse generation on the nanoscale, and the lack of successful implementations. Here, we address this problem in a study of highly nonlinear optical processes in gas-exposed bow-tie nanoantennas. We find multiphoton- and strong-field-induced atomic excitation and ionization resulting in extreme-ultraviolet fluorescence, as well as third- and fifth-harmonic generation intrinsic to the nanostructures. Identifying the intensity-dependent spectral fingerprint of atomic fluorescence, we gauge local plasmonic fields. Whereas intensities sufficient for high-harmonic generation are indeed achieved in the near-field, the nanoscopic volume is found to prohibit an efficient conversion. Our results illustrate opportunities and challenges in highly nonlinear plasmonics and its extension to the extreme ultraviolet.Deutsche Forschungsgemeinschaft [DFG-ZUK 45/1, SFB 755
MBE growth of high electron mobility 2DEGs in AlGaN/GaN heterostructures controlled by RHEED
No full textWe have grown 2DEG AlGaN/GaN heterostructures by molecular beam epitaxy (MBE) with electron mobilities up to 21500 cm2V−1s−1 at 2 K. In-situ RHEED was applied to optimize different aspects of Ga-rich growth. This paper gives a compact overview of the experimental key aspects that significantly affect the low temperature electron mobility in AlGaN/GaN heterostructures. Growth at the transition towards Ga droplet formation produced the best results. A quantitative analysis of the magnetoresistance confirmes scattering at dislocations as the dominant scattering process at low temperature
Nanotip-based photoelectron microgun for ultrafast LEED
No full textWe present the design and fabrication of a micrometer-scale electron gun for the
implementation of ultrafast low-energy electron diffraction from surfaces. A multi-step
process involving photolithography and focused-ion-beam nanostructuring is used to assemble and
electrically contact the photoelectron gun, which consists of a nanotip photocathode in a
Schottky geometry and an einzel lens for beam collimation. We characterize the low-energy
electron pulses by a transient electric field effect and achieve pulse durations of 1.3 ps
at an electron energy of 80 eV. First diffraction images in a backscattering geometry (at 50
eV electron energy) are shown
Analysis of the Height Transformations of the Geodetic Plans
No full textV diplomski nalogi obravnavamo metode določitve razlik med starim in novim državnim višinskim koordinatnim sistemom ter pretvarjanje med njima. Pretvorbe smo izvedli s pomočjo spletne aplikacije SiVis, ki omogoča dokaj enostavno in hitro transformacijo med sistemi ter na podlagi podatkov o višinah okoliških reperjev državne nivelmanske mreže. Kot podlaga za analizo smo uporabili detajlne točke treh geodetskih načrtov na različnih lokacijah v Sloveniji. Glede na rezultate pretvorb na različne načine smo ugotovili prednosti in slabosti posameznih metod. V splošnem velja, da je pretvorba višin na podlagi okoliških reperjev bolj natančna kot uporaba spletne aplikacije SiVis.The purpose of this Graduation Thesis is to understand the difference between the old and new Slovenian Height Coordinate System and to convert between those two. We did the transformations with the help of internet aplication SiVis, which enables easy and quick transformation between the two and based on the surrounding benchmark of national levelling network. The base for analysis are the points of three different Geodetic Plans around the country. The best method of transformation was then chosen according to the results of transformations. To get better results of transformation in general it is better to use the surrounding benchmarks rather than to transformate with the use of SiVis
Electronic and structural fingerprints of charge density wave excitations in extreme ultraviolet transient absorption spectroscopy
No full textFemtosecond core-level transient absorption spectroscopy is utilized to
investigate photoinduced dynamics of the charge density wave in 1T-TiSe2 at the
Ti M2,3 edge (30-50 eV). Photoexcited carriers and phonons are found to
primarily induce spectral red-shifts of core-level excitations, and a carrier
relaxation time and phonon heating time of approximately 360 fs and 1.0 ps are
extracted, respectively. Pronounced oscillations in delay-dependent absorption
spectra are assigned to coherent excitations of the optical phonon
(6.0 THz) and the charge density wave amplitude mode (3.3 THz). By
comparing the measured spectra with time-dependent density functional theory
simulations, we determine the directions of the momentary atomic displacements
of both coherent modes and estimate their amplitudes. This work presents a
first look on charge density wave excitations with table-top core-level
transient absorption spectroscopy, enabling simultaneous access to electronic
and lattice excitation and relaxation
Coherent diffractive imaging beyond the projection approximation: Waveguiding at extreme ultraviolet wavelengths
No full textWe study extreme-ultraviolet wave propagation within optically thick nanostructures by means of high-resolution coherent diffractive imaging using high-harmonic radiation. Exit waves from different objects are reconstructed by phase retrieval algorithms, and are shown to be dominated by waveguiding within the sample. The experiments provide a direct visualization of extreme-ultraviolet guided modes, and demonstrate that multiple scattering is a generic feature in extruded nanoscale geometries. The observations are successfully reproduced in numerical and semi-analytical simulations
Highly Nonlinear and Ultrafast Optical Phenomena in Metallic Nanostructures
No full textThis Chapter presents recent findings on nonlinear ionization and photoemission processes at metallic nanostructures. A particular emphasis is placed on processes which—due to the localized excitation in optical near-fields—exhibit different properties and scalings from their counterparts in the gas phase or at planar surfaces. The Chapter is structured in two parts. The first part discusses various regimes in highly nonlinear photoelectron emission from metallic nanotips, including field-driven photoemission at near- and mid-infrared frequencies, and the control of localized photoemission using intense terahertz transients. In the second part, multiphoton and strong-field ionization of atomic gases in plasmonic antennas and waveguides is presented. It is demonstrated that local ionization is enabled by optical field enhancements in various types of structures. At the same time, fundamental physical limitations preventing efficient high-harmonic generation in nanostructures are discussed.This Chapter presents recent findings on nonlinear ionization and photoemission processes at metallic nanostructures. A particular emphasis is placed on processes which—due to the localized excitation in optical near-fields—exhibit different properties and scalings from their counterparts in the gas phase or at planar surfaces. The Chapter is structured in two parts. The first part discusses various regimes in highly nonlinear photoelectron emission from metallic nanotips, including field-driven photoemission at near- and mid-infrared frequencies, and the control of localized photoemission using intense terahertz transients. In the second part, multiphoton and strong-field ionization of atomic gases in plasmonic antennas and waveguides is presented. It is demonstrated that local ionization is enabled by optical field enhancements in various types of structures. At the same time, fundamental physical limitations preventing efficient high-harmonic generation in nanostructures are discussed
Sivis, Florence (Birth, 1905-06-13)
No full textAddress: 2122 Hatmaker2528/Pg 61/1905/M W/Cinti/Cinti/Mrs. A. SchultiamOriginal record filed in drawer labeled 'SLIVER-SLOMER'
