The Experts below are selected from a list of 17226 Experts worldwide ranked by ideXlab platform
O. Santolík - One of the best experts on this subject based on the ideXlab platform.
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power line Harmonic Radiation observed by the demeter spacecraft at 50 60 hz and low Harmonics
Journal of Geophysical Research, 2015Co-Authors: F. Němec, O. Santolík, Michel ParrotAbstract:We present a low-altitude satellite survey of Power Line Harmonic Radiation (PLHR), i.e., electromagnetic waves radiated by electric power systems on the ground. We focus on frequencies corresponding to the first few Harmonics of the base power system frequencies (50 Hz or 60 Hz, depending on the region). It is shown that the intensities of electromagnetic waves detected at these frequencies at an altitude of about 700 km are significantly enhanced above industrialized areas. The frequencies at which the wave intensities are increased are in excellent agreement with base power system frequencies just below the satellite location. We also investigate a possible presence of the weekend effect, i.e., if the situation is different during the weekends when the power consumption is lower than during the weekdays. Such an effect might be possibly present in the European region, but it is very weak. PLHR effects are less often detected in the summer, as the ionospheric absorption increases, and also, the Radiation is obscured by lightning generated emissions. This difference is smaller in the U.S. region, in agreement with the monthly variations of the power consumption. The analysis of the measured frequency spectra reveals that although intensity increases at low odd Harmonics of base power system frequencies are routinely detected, low even Harmonics are generally absent. Finally, we verify the relation of PLHR intensities to the geomagnetically induced currents (GICs) proxy. It is shown that the PLHR intensity is increased at the times of higher GIC proxy values during the night.
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statistical analysis of vlf radio emissions triggered by power line Harmonic Radiation and observed by the low altitude satellite demeter
Journal of Geophysical Research, 2014Co-Authors: Michel Parrot, Frantisek Nĕmec, O. SantolíkAbstract:DEMETER was a low-altitude satellite in operation between 2004 and 2010 in a circular polar orbit. One of its main scientific objectives was to study ionospheric perturbations related to man-made activity. This paper investigates electromagnetic emissions triggered by Power Line Harmonic Radiation (PLHR), the man-made waves emitted at Harmonics of 50 or 60 Hz. They look like rising tones or hooks with a starting frequency associated to a parent line with the frequency equal to a multiple of 50 or 60 Hz. They occur preferentially during daytime in a frequency band between 1 and 4 kHz. It is shown that these emissions are rather frequent at high latitudes (3 < L <6) above industrialized areas during periods of moderate magnetic activity. Their average intensity is of the order of 10 μV 2 m A2 Hz A1. PLHR propagates in the magnetosphere and triggers emissions due to wave-particle interactions in the equatorial region.
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Power line Harmonic Radiation observed by satellite: Properties and propagation through the ionosphere
Journal of Geophysical Research Space Physics, 2008Co-Authors: F. Němec, O. Santolík, Michel Parrot, J. BortnikAbstract:We present results of a systematic survey of power line Harmonic Radiation events observed by the low-altitude DEMETER spacecraft. Altogether, 88 events (45 with frequency spacing 50/100 Hz and 43 with frequency spacing 60/120 Hz) have been found by an automatic identification procedure and confirmed by visual inspection. Frequency-Time intervals of individual lines forming the events have been found by an automated procedure, and the corresponding frequency-time spectrograms have been fitted by a 2d-Gaussian model. It is shown that the mean time duration of the lines forming the events is 20 seconds, with median being 12 seconds (this corresponds to the spatial dimensions of 156/90 km, respectively). The full width at half maximum of the frequency range of the lines is less than 3 Hz in the majority of cases. Moreover, the lines with larger bandwidth and the lines with the largest intensities often occur off exact multiples of base power system frequency. This can be explained either by wave-particle interactions that take place and modify the radiated electromagnetic wave or by the improperly operating radiating power system. Full-wave calculation of the efficiency of coupling of electromagnetic waves through the ionosphere has been done to show that it can explain lower intensity of events observed by satellite during the day as compared with those observed during the night. Estimated radiated peak power on the ground is larger for events observed during the day than for events observed during the night, and more events are observed during the day than during the night.
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Comparison of magnetospheric line Radiation and power line Harmonic Radiation: A systematic survey using the DEMETER spacecraft
Journal of Geophysical Research Space Physics, 2007Co-Authors: F. Němec, O. Santolík, Michel Parrot, Jean-jacques BerthelierAbstract:Results of a systematic search for magnetospheric line Radiation (MLR) observed by the DEMETER spacecraft since the beginning of the mission are presented. DEMETER is a French microsatellite (altitude of orbit about 700 km, inclination 98°) designed to study electromagnetic phenomena connected with seismic or man-made activity that has been launched in June 2004. An automatic identification procedure of possible MLR events has been used in order to analyze a large amount of measured data. It is shown that there are two principally different classes of events: (1) events with frequency spacing of 50/100 or 60/120 Hz (power line Harmonic Radiation, PLHR) and (2) events with a different frequency spacing. The first class of events is generated by power systems on the Earth's surface, with frequency spacing well corresponding to the fundamental frequency of the radiating power system. On the other hand, the second class is most probably generated in a completely natural way. All the detected events are thoroughly analyzed, and different properties of the two classes are statistically demonstrated. We have found that PLHR events occur both during low and high geomagnetic activity, with none of them significantly preferred. However, MLR events occur more frequently under disturbed conditions. Most of the PLHR events are observed at frequencies of 2 to 3 kHz. On the other hand, MLR events most frequently occur at frequencies below 2 kHz and seem to be more intense than PLHR. Additionally, PLHR events are more intense during the night than during the day, and there is about the same number of PLHR events observed during the day and during the night. On the contrary, no dependence of MLR peak intensities on magnetic local time was found, and more MLR events were observed during the day than during the night, although this difference is not statistically very significant. Finally, there is a group of MLR events with characteristics corresponding to the previous spacecraft observations of equatorial noise.
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Power line Harmonic Radiation (PLHR) observed by the DEMETER spacecraft
Journal of Geophysical Research, 2006Co-Authors: F. Němec, O. Santolík, Michel Parrot, Jean-jacques BerthelierAbstract:Results of a systematic survey of Power Line Harmonic Radiation (PLHR) observed by a recently (June 2004) launched French spacecraft DEMETER are presented. In order to obtain a statistically significant number of events, an automatic identification procedure has been developed and all the available high-resolution data have been processed. Altogether, 58 events have been found in 865 hours of data recorded during the first year of operation. These events form three different classes: with frequency spacing of spectral lines of 50/100 Hz (10 events), with frequency spacing of 60/120 Hz (13 events), with other spacings/not clear cases (35 events). The first two classes of events are discussed in detail, showing that their origin is most probably connected with the Radiation from the electric power systems which are magnetically conjugated with the place of observation. Additionally, in more than one half of the cases, the frequencies of PLHR lines well corresponded to the multiples of the power system frequency. The frequency drift of all the observed events was very slow, if observable. The events occurred without any significant preference for low or high geomagnetic activity, although more intense events were observed during disturbed times. Simultaneous observations of electric and magnetic components of PLHR suggest that the waves propagate in the electromagnetic right-hand polarized whistler mode.
Christoph H Keitel - One of the best experts on this subject based on the ideXlab platform.
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exotic atoms in superintense laser fields applications in atomic nuclear and particle physics
European Physical Journal-special Topics, 2009Co-Authors: Carsten Muller, Karen Zaven Hatsagortsyan, Atif Shahbaz, Thomas J Burvenich, Christoph H KeitelAbstract:The interaction of very strong laser fields with hydrogenlike atomic systems is analyzed theoretically. It is shown that the usual magnetic field-induced limitations for efficient recollisions can be overcome by employing exotic atoms rather than ordinary ones. In this way not only high-Harmonic Radiation in the MeV regime could be produced, but also laser-induced nuclear effects and particle reactions come into the reach of near-future laser facilities.
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coherent hard x rays from attosecond pulse train assisted Harmonic generation
Optics Letters, 2008Co-Authors: Michael Klaiber, Karen Zaven Hatsagortsyan, Carsten Muller, Christoph H KeitelAbstract:High-order Harmonic generation from atomic systems is considered in the crossed fields of a relativistically strong infrared laser and a weak attosecond pulse train of soft x rays. Due to one-photon ionization by the x-ray pulse, the ionized electron obtains a starting momentum that compensates the relativistic drift, which is induced by the laser magnetic field, and allows the electron to efficiently emit Harmonic Radiation upon recombination with the atomic core in the relativistic regime. This way, short pulses of coherent hard x rays of up to 40keV energy can be generated.
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coherent hard x rays from attosecond pulse train assisted Harmonic generation
arXiv: Atomic Physics, 2007Co-Authors: Michael Klaiber, Karen Zaven Hatsagortsyan, Carsten Muller, Christoph H KeitelAbstract:High-order Harmonic generation from atomic systems is considered in the crossed fields of a relativistically strong infrared laser and a weak attosecond-pulse train of soft x-rays. Due to one-photon ionization by the x-ray pulse, the ionized electron obtains a starting momentum that compensates the relativistic drift which is induced by the laser magnetic field, and allows the electron to efficiently emit Harmonic Radiation upon recombination with the atomic core in the relativistic regime. In this way, short pulses of coherent hard x-rays of up to 40 keV energy and 10 as duration can be brought about.
C V Shank - One of the best experts on this subject based on the ideXlab platform.
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observation of laser assisted photoelectric effect and femtosecond high order Harmonic Radiation
Physical Review Letters, 1996Co-Authors: T E Glover, R W Schoenlein, A H Chin, C V ShankAbstract:We report the first observation of laser-induced free-free transitions in the primary photoelectron spectra of gaseous helium ionized by ultrashort soft x-ray pulses. Measured transition amplitudes are well described by projecting the initial electronic state onto a Volkov wavefunction. Additionally, we report the first direct measurements on the temporal duration of femtosecond high order Harmonic Radiation. The Harmonic pulse duration is observed to exhibit strong dependencies upon both laser intensity and position of the generating medium relative to the laser focus.
Michael Klaiber - One of the best experts on this subject based on the ideXlab platform.
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coherent hard x rays from attosecond pulse train assisted Harmonic generation
Optics Letters, 2008Co-Authors: Michael Klaiber, Karen Zaven Hatsagortsyan, Carsten Muller, Christoph H KeitelAbstract:High-order Harmonic generation from atomic systems is considered in the crossed fields of a relativistically strong infrared laser and a weak attosecond pulse train of soft x rays. Due to one-photon ionization by the x-ray pulse, the ionized electron obtains a starting momentum that compensates the relativistic drift, which is induced by the laser magnetic field, and allows the electron to efficiently emit Harmonic Radiation upon recombination with the atomic core in the relativistic regime. This way, short pulses of coherent hard x rays of up to 40keV energy can be generated.
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coherent hard x rays from attosecond pulse train assisted Harmonic generation
arXiv: Atomic Physics, 2007Co-Authors: Michael Klaiber, Karen Zaven Hatsagortsyan, Carsten Muller, Christoph H KeitelAbstract:High-order Harmonic generation from atomic systems is considered in the crossed fields of a relativistically strong infrared laser and a weak attosecond-pulse train of soft x-rays. Due to one-photon ionization by the x-ray pulse, the ionized electron obtains a starting momentum that compensates the relativistic drift which is induced by the laser magnetic field, and allows the electron to efficiently emit Harmonic Radiation upon recombination with the atomic core in the relativistic regime. In this way, short pulses of coherent hard x-rays of up to 40 keV energy and 10 as duration can be brought about.
U Kleineberg - One of the best experts on this subject based on the ideXlab platform.
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generation of circularly polarized high Harmonic Radiation using a transmission multilayer quarter waveplate
Optics Express, 2015Co-Authors: J Schmidt, Alexander Guggenmos, Michael Hofstetter, Soo Hoon Chew, U KleinebergAbstract:High Harmonic Radiation is meanwhile nearly extensively used for the spectroscopic investigation of electron dynamics with ultimate time resolution. The majority of high Harmonic beamlines provide linearly polarized Radiation created in a gas target. However, circular polarization greatly extends the spectroscopic possibilities for high Harmonics, especially in the analysis of samples with chirality or prominent spin polarization. We produced a free-standing multilayer foil as a transmission EUV quarter waveplate and applied it for the first time to high Harmonic Radiation. We measured a broadband (4.6 eV FWHM) ellipticity of 75% at 66 eV photon energy with a transmission efficiency of 5%. The helicity is switchable and the ellipticity can be adjusted to lower values by angle tuning. As a single element it can be easily integrated in any existing Harmonic beamline without major changes.
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toward time resolved soft x ray microscopy using pulsed fs high Harmonic Radiation
Ultramicroscopy, 2005Co-Authors: Marek Wieland, U Kleineberg, Christian Spielmann, T Westerwalbesloh, Ulrich Heinzmann, T WilheinAbstract:Coherent soft X-ray sources open the way to new capabilities in high-resolution imaging, site- and element-specific spectroscopy and biomicroscopy. In this paper we demonstrate imaging with a table-top soft X-ray microscope. By combining a laser driven high-Harmonic light source, optimized for having the maximum brightness at around 100 eV, a pair of multilayer mirrors to select a narrow spectral band and acting simultaneously as a condenser and a Fresnel zone plate as microscope objective, we were able to resolve 200 nm structures of a diatom sample. Further, the pulsed nature of our X-ray source offers the possibility of time-resolved spectromicroscopy with a temporal resolution in the order of a few femtoseconds.
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submicron extreme ultraviolet imaging using high Harmonic Radiation
Applied Physics Letters, 2002Co-Authors: Marek Wieland, Rolf Frueke, T Wilhein, Christian Spielmann, Martin Pohl, U KleinebergAbstract:We report on experiments using high-Harmonic (HH) Radiation for microscopy imaging at 13 nm wavelength. A simple setup using a zone plate as objective and a back-illuminated CCD as detector yields at moderate magnifications of M≈60 a spatial resolution of δx<0.8 μm demonstrated with a sample of mica. The HH Radiation was monochromatized by means of a high-efficiency multilayer monochromator consisting of two Mo/Si-mirros.
