Spatial coherence properties of 3 different kinds of coherent sources in extreme ultraviolet/soft x‐ray wavelength region, namely undulator, x‐ray laser and high harmonic generation source, are introduced. Advantage...
Spatial coherence properties of 3 different kinds of coherent sources in extreme ultraviolet/soft x‐ray wavelength region, namely undulator, x‐ray laser and high harmonic generation source, are introduced. Advantages of each source type and their potential applications are also discussed.
Exciton-polariton structures were observed at 8 K in the photoreflectance (PR) and resonantly excited photoluminescence (PL) spectra of a ZnO (0001) epitaxial film on the a -face of sapphire grown by radical-source mo...
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Exciton-polariton structures were observed at 8 K in the photoreflectance (PR) and resonantly excited photoluminescence (PL) spectra of a ZnO (0001) epitaxial film on the a -face of sapphire grown by radical-source molecular-beam epitaxy. The resonance energies of near-normal predominant PR structures were close to those of the longitudinal excitons, i.e. upper polariton branches, where A-, B-, and C-excitons couple simultaneously to an electromagnetic wave. In contrast to the results obtained for GaN, the longitudinal–transverse (L–T) splitting of the B-excitonic polariton was observed, which is due to the large oscillator strength. The sample quality was high enough to observe distinct excitonic polariton emissions.
Many work related electric accidents occurred in electric energy industries and they were very often fatal. The situation of electric accidents in electric companies worldwide is investigated by reviewing the scientif...
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This paper describes the layered and modular hard- and software architecture of autonomously soccer playing robots used in The Dutch Team. The schemes of the hard and software architectures are presented and the softw...
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Recombination dynamics of localized excitons in strained cubic (c-)In x Ga 1— x N/c-GaN multiple quantum wells (MQWs) were studied. In contrast to hexagonal (h-)InGaN quantum wells (QWs), low-excitation photoluminesc...
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Recombination dynamics of localized excitons in strained cubic (c-)In x Ga 1— x N/c-GaN multiple quantum wells (MQWs) were studied. In contrast to hexagonal (h-)InGaN quantum wells (QWs), low-excitation photoluminescence (PL) peak energy increased moderately with decreasing well thickness L and the PL decay time did not depend on L . The results indicated that piezoelectric field had negligible influence on the transition processes. The time-resolved photoluminescence (TRPL) signal showed a stretched exponential decay up to 300 K, showing that the spontaneous emission is due to the radiative recombination of excitons localized in disordered quantum nanostructures even at 300 K. Decrease in internal quantum efficiency ( η ), which is related to the increase in quasi-radiative lifetime, with the increase in temperature was explained to be due to reduced localization rate.
Change of device characteristics of the metal-ferroelectric-semiconductor FET (MFSFET) with the progress of fatigue of the ferroelectric thin film are simulated in this study. The field-dependent polarization model an...
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Summary form only given. Sub-femtosecond, electromagnetic pulses, of much interest presently, are short on the time scale of condensed-matter processes. Six orders of magnitude, however, separate them from the next ti...
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Summary form only given. Sub-femtosecond, electromagnetic pulses, of much interest presently, are short on the time scale of condensed-matter processes. Six orders of magnitude, however, separate them from the next time scale of interest, that of nuclear interactions (10/sup -21/-10/sup -22/ s). Such pulses seem so much out of reach today that no one so far has considered their feasibility. In this paper, we demonstrate theoretically that such pulses can in fact be generated using a Petawatt laser, while more widely available terawatt lasers may generate sub-attosecond pulses. The pulses would be radiated by electrons rotating ultra-relativistically in high-intensity laser fields. It is basically synchrotron radiation; however, no synchrotron can even come close to running electrons with the energy of 50 MeV around a circle of 0.1 /spl mu/m radius, as a Petawatt laser can. We will call such a system "lasertron.".
Summary form only given. Tunable multi-wavelength fiber laser sources have numerous applications in optical and RF communications and optical sensing. Specific applications include wavelength division multiplexing, wi...
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Summary form only given. Tunable multi-wavelength fiber laser sources have numerous applications in optical and RF communications and optical sensing. Specific applications include wavelength division multiplexing, wideband RF signal processing, multielement optical sensors, and optical soliton sources. To date, multi-wavelength operation and tunable single wavelength operation of fiber lasers have been demonstrated. The ability to adjust the channel spacing and tune the absolute frequency in a multi-wavelength laser system can provide many degrees of freedom in the fiber laser design. In this paper, we discuss a method for discretely tuning the channel spacing by using a polarization controller and experimentally demonstrate this concept with a dual-wavelength fiber laser source. We have recently demonstrated the continuous tuning capability of this source.
As a result of the interaction with an operating wave in a relativistic backward wave oscillator (BWO), electrons end up with a large energy spread regardless of the efficiency of operation of the oscillator. Calculat...
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As a result of the interaction with an operating wave in a relativistic backward wave oscillator (BWO), electrons end up with a large energy spread regardless of the efficiency of operation of the oscillator. Calculations show that the distribution of electron density as a function of energy is almost symmetric in relation to the average electron energy after transfer of part of electron's energy to the electromagnetic field. One portion of the distribution has electron energy that is significantly greater than the initial one, while the other portion has smaller electron energy that leads to a decrease of the transported current, limited by the electrons' own space charge. Local virtual cathodes can appear in the output channel. A portion of the reflected electrons reaches the cathode, decreasing its emission and leading to a modulation of the output radiation. The amplitude and spectrum of the modulation depend on the circumstances of the beam dump for spent electrons. In experiments with an X-band relativistic BWO, an increase of the microwave radiation pulse duration was observed when the electron beam dump was placed close to the interaction space. Pulse shortening could be caused by a decrease of electron emission due to reflected electrons decreasing the beam current below the start current. Therefore, conditions in the beam dump can interrupt the regime of stationary generation.
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