956 research outputs found
Plasmon-enhanced extreme-ultraviolet light generation: Challenges and future perspectives
No full textWe present a study of plasmon-enhanced gas excitation and extreme-ultraviolet (EUV) light generation in bow-tie antennas and tapered hollow waveguides. The observed EUV emission corresponds to incoherent atomic and ionic fluorescence without any sign from coherent highharmonic generation
Generation and Bistability of a Waveguide Nanoplasma Observed by Enhanced Extreme-Ultraviolet Fluorescence
No full textWe present a study of the highly nonlinear optical excitation of noble gases in tapered hollow waveguides using few-femtosecond laser pulses. The local plasmonic field enhancement induces the generation of a nanometric plasma, resulting in incoherent extreme-ultraviolet fluorescence from optical transitions of neutral and ionized xenon, argon, and neon. Despite sufficient intensity in the waveguide, high-order harmonic generation is not observed. The fluorescent emission exhibits a strong bistability manifest as an intensity hysteresis, giving strong indications for multistep collisional excitations.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
An ultrafast nanotip electron gun triggered by grating-coupled surface plasmons
No full textWe demonstrate multiphoton photoelectron emission from gold nanotips induced by nanofocusing surface plasmons, resonantly excited on the tip shaft by a grating coupler. The tip is integrated into an electron gun assembly, which facilitates control over the spatial emission sites and allows us to disentangle direct grating emission from plasmon-triggered apex emission. The nanoscale source size of this electron gun concept enables highly coherent electron pulses with applications in ultrafast electron imaging and diffraction. (C) 2015 AIP Publishing LLC.Deutsche Forschungsgemeinschaft (DFG) [SFB-1073
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
Clocking plasmon nanofocusing by THz near-field streaking
No full textWe apply terahertz (THz) near-field streaking in a nanofocusing geometry to investigate plasmon polariton propagation on the shaft of a conical nanotip. By evaluating the delay between a streaking spectrogram for plasmon-induced photoemission with a measurement for direct apex excitation, we obtain an average plasmon group velocity, which is in agreement with numerical simulations. Combining plasmon-induced photoemission with THz near-field streaking facilitates extensive control over localized photoelectron sources for time-resolved imaging and diffraction
Polarization contrast of nanoscale waveguides in high harmonic imaging
No full textThe optical polarization response of a structured material is one of its most significant properties, carrying information about microscopic anisotropies as well as chiral features and spin orientations. Polarization analysis is therefore a key element of imaging and spectroscopy techniques throughout the entire spectrum. In the case of extreme ultraviolet (EUV) radiation, however, both the preparation and detection of well-defined polarization states remain challenging. As a result, polarization-sensitive EUV microscopy based on table-top sources has not yet been realized, despite its great potential, for example, in nanoscale magnetic imaging. Here, we demonstrate polarization contrast in coherent diffractive imaging using high harmonic radiation and investigate the polarization properties of nanoscale transmission waveguides. We quantify the achievable polarization extinction ratio for different waveguide geometries and wavelengths. Our results demonstrate the utility of slab waveguides for efficient EUV polarization control and illustrate the importance of considering polarization contrast in the imaging of nanoscale structures. (C) 2016 Optical Society of Americ
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
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