The Experts below are selected from a list of 25374 Experts worldwide ranked by ideXlab platform
K Kikuchi - One of the best experts on this subject based on the ideXlab platform.
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narrowband optical filter with a variable transmission spectrum using stimulated brillouin scattering in optical fiber
Optics Letters, 2002Co-Authors: Takuo Tanemura, Yuichi Takushima, K KikuchiAbstract:A novel shape-adjustable narrowband optical filter utilizing stimulated Brillouin scattering in an optical fiber is proposed and demonstrated. In this scheme, binary-phase-shift-keying modulation is applied to the Pump Wave to broaden and shape the Brillouin gain spectrum. By choosing an appropriate modulation data pattern, we realized a flat-top steep-cutoff optical bandpass filter with a 3-dB bandwidth of 1.5 GHz and a 10-dB bandwidth of 2 GHz is realized. In addition, a tunable optical notch filter is also realized by deamplification of the anti-Stokes Wave.
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Suppression of idler spectral broadening in highly efficient fiber four-Wave mixing by binary-phase-shift-keying modulation of Pump Wave
IEEE Photonics Technology Letters, 2001Co-Authors: T. Tanemura, K KikuchiAbstract:Proposes and demonstrates a novel method of suppressing spectral broadening of the idler Wave, which is generated in fiber four-Wave mixing (FWM) Pumped by a continuous Wave. In this scheme, binary-phase-shift-keying (BPSK) modulation of the Pump Wave broadens the Pump spectrum so that the Brillouin threshold for the Pump power is increased, whereas it never affects the spectrum of the idler Wave. By the 2-Gb/s BPSK modulation of the Pump Wave, we achieve a FWM efficiency as high as 10 dB, maintaining a side-band suppression ratio of the idler Wave larger than 25 dB.
V L Frolov - One of the best experts on this subject based on the ideXlab platform.
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On Spatial Structuring of the F2 Layer Studied by the Satellite Radio Sounding of the Ionosphere Disturbed by High-Power HF Radio Waves
Radiophysics and Quantum Electronics, 2018Co-Authors: E. D. Tereshchenko, V. A. Turyansky, B. Z. Khudukon, R. Yu. Yurik, V L FrolovAbstract:We present the results of studying the characteristics of the artificial plasma structures excited in the ionospheric F_2 region modified by high-power HF radio Waves. The experiments were carried out at the Sura heating facility using satellite radio sounding of the ionosphere. The plasma density profile was reconstructed with the highest possible spatial resolution for today, about 4 km. In a direction close to the magnetic zenith of the Pump Wave, the following phenomena were observed: the formation of a cavity with a 15% lower plasma density at the altitudes of the F_2 layer and below; the formation of an area with plasma density increased by 12% at altitudes greater than 400 km. With a long-term quasiperiodic impact of the Pump Wave on the ionosphere, wavy large-scale electron-density perturbations (the meridional scale λ_x ≈ 130 km and the vertical scale λ_z ≈ 440 km) are also formed above the Sura facility. These perturbations can be due to the plasma density modulation by an artificial acoustic-gravity Wave with a period of 10.6 m, which was formed by the heat source inside a large-scale cavity with low plasma density; there is generation of the electron density irregularities for the electrons with ΔN_e/N_e ≈ 3% in the form of layers having the sizes 10–12 km along and about 24 km across the geomagnetic field, which are found both below and above the F_2-layer maximum. The mechanisms of the formation of these plasma structures are discussed.
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Peculiarities of Excitation of Large-Scale Plasma Density Irregularities During Modification of the Ionospheric F _2 Region by High-Power HF Radio Waves
Radiophysics and Quantum Electronics, 2016Co-Authors: V L Frolov, E. A. Schorokhova, V. E. Kunitsyn, E. S. Andreeva, A. M. PadokhinAbstract:We present the experimental results concerning the features of large-scale artificial plasma-density irregularities excited in the ionospheric F_2 region by high-power HF radio Waves. The experiments were performed in recent years using the SURA heating facility. It is shown that at the altitude of the Pump-Wave reflection, these irregularities are most efficiently generated in the magnetic zenith region. The effect of enhancement of the large-scale irregularity generation at the edge of the Pump-Wave beam is revealed. The results of studying large-scale irregularities recorded at the altitudes of the topside ionosphere are presented. Experimental results concerning the features of the internal gravity Waves generated at the ionospheric altitudes during periodic heating of the ionospheric plasma by high-power HF radio Waves are summarized and their possible influence on generation of artificial ionospheric irregularities at a long distance from the heater is discussed.
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Gyroharmonic features of the hf-induced ionospheric irregularities
Radiophysics and Quantum Electronics, 2012Co-Authors: V L Frolov, G P Komrakov, I. A. Bolotin, G. G.vertogradov, V. G. Vertogradov, E. G. Vertogradova, A. D. Akchurin, V. V. Bochkarev, A. M. Dresher, E. Yu. ZykovAbstract:Gyroharmonic features of the different-scale artificial plasma-density irregularities excited by HF modification of the ionospheric F_2 region under conditions where the frequency of the O-mode Pump Wave is close to the fourth gyroharmonic frequency of electrons in the Pump Wave—plasma interaction region are considered.
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Gyroharmonic properties of the middle-scale artificial ionospheric turbulence during heating of the ionospheric F _2 layer by a high-power O-mode radio Wave
Radiophysics and Quantum Electronics, 2008Co-Authors: V L Frolov, D. I. Nedzvetsky, V. P. Uryadov, V. A. Ivanov, D. V. Ivanov, A. R. Lashchevsky, N. V. RyabovaAbstract:We present the results of studying the properties of artificial F-spread that appears on ionograms during heating of the ionospheric F_2 region by a high-power O-mode radio Wave. It is shown that the regions of resonant interaction of a high-power radio Wave with plasma, where the Pump-Wave energy is almost totally absorbed and the plasma is subject to intense heating, affect significantly the development of a self-focusing instability of a high-power radio Wave and the generation of middle-scale (with characteristic scales across the magnetic field l_⊥ ≈ 0.4–1.5 km) artifical ionospheric inhomogeneities. It is established that the intensity of such inhomogeneities depends on the sign and magnitude of detuning of the Pump-Wave frequency with respect to the electron gyroresonance harmonic frequency Δf = f_PW − nf_ce and has the minimum value for Δf ≈ −20 kHz, thus demonstrating the asymmetry of the gyroharmonic properties of their excitation mechanism. Relationship between the observed phenomena and known characteristics of the artificial ionospheric turbulence for f_PW ≈ nf_ce is analyzed.
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On specific features of diurnal variations in characteristics of the diagnostic stimulated electromagnetic emission and their relation to the evolution of artificial ionospheric irregularities
Radiophysics and Quantum Electronics, 2008Co-Authors: V L Frolov, G. G. Vertogradov, V. G. VertogradovAbstract:We analyze variations in characteristics of the diagnostic stimulated electromagnetic emission of the ionosphere in the evening hours including the times of sunset both on the Earth’s surface at the observation point and in the ionosphere over it. It is found that an increase in typical times of evolution of the diagnostic emission begins to be recorded just before the sunset on the Earth’s surface when the ionosphere is illuminated and its parameters are not significantly changed yet. We state that the typical times of evolution of the diagnostic emission increase when the Pump-Wave frequency approaches the critical frequency of the ionospheric F_2 layer, but such an effect is not as significant as when passing from the illuminated to the unilluminated ionosphere. It is established that at the stage of diagnostic sounding the Pump-Wave pulse power does not exert any notable influence on the first (fast) stage of relaxation of small-scale artificial ionospheric irregularities, but can increase the decay time of the irregularities at the second (slow) stage of relaxation. Capabilities of the method for a study of artificial plasma turbulence using the diagnostic stimulated electromagnetic emission are discussed.
E. N. Sergeev - One of the best experts on this subject based on the ideXlab platform.
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Spectra of Stimulated Electromagnetic Emission of the Ionosphere Sweeping of the Pump Wave Frequency Near Gyroharmonics. II. Discussion of the Results
Radiophysics and Quantum Electronics, 2008Co-Authors: S. M. Grach, E. N. Sergeev, V. A. Yashnov, P. V. KotovAbstract:Alternative mechanisms of generation of the stimulated electromagnetic emission (SEE) excited in the ionosphere by high-power radio Waves are analyzed on the basis of measurements of the SEE spectra obtained during the Pump-Wave frequency sweeping near the forth (n = 4) and fifth (n = 5) harmonics of the electron gyrofrequency nf_ce [ 1 ] and their comparison with the existing physical models. A method for determination of the magnetic field strength and plasma density near the double-resonance region in the ionosphere is developed. It is shown that the generation of the broad upshifted maximum (BUM) feature in the SEE spectrum should occur several kilometers below the double-resonance altitude. A role of high-frequency plasma modes and small-scale magnetic field-aligned irregularities, excited under ionosphere Pumping by a high-power radio Wave, in the formation of SEE spectra is demonstrated. It is shown that the difference in the emission intensities for f_0 ≲ nf_ce and f_0 > nf_ce is related to different regions (altitudes) at which the plasma Waves exist in these cases.
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Spectra of Stimulated Electromagnetic Emission of the Ionosphere Upon Sweeping of the Pump Wave Frequency Near Gyroharmonics. I. Experimental Results
Radiophysics and Quantum Electronics, 2008Co-Authors: P. V. Kotov, E. N. Sergeev, S. M. GrachAbstract:We present the results of experimental studies of the spectra of the stimulated electromagnetic emission excited in the ionosphere by powerful radio Waves during the Pump Wave frequency sweeping near the forth ( n = 4) and fifth ( n = 5) harmonics of the electron cyclotron frequency nf _ce. The frequency sweep was carried out for long (continuous) Pumping in vertical and inclined directions (at 14° and 18° south of the zenith), as well as for the pulse diagnostic Wave both with and without additional Pumping far from the gyroharmonics. The dependences of the spectral features of the stimulated electromagnetic emission on the ratio between the Pump-Wave frequency f _0 (or on the diagnostic-Wave frequency f_DW) and nf _ce were analyzed. It is found that near the multiple gyroresonance, different spectral features of the stimulated emission are quenched at the same frequency for different Pump-Wave frequencies. For a sufficiently large inclination of the Pump Wave beam from the vertical direction, the intensity of the stimulated electromagnetic emission is notably decreased for f _0 ≲ nf _ce as compared with f _0 > nf _ce.
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on the morphology of stimulated electromagnetic emission spectra in a wide Pump Wave frequency range
Advances in Space Research, 2006Co-Authors: E. N. Sergeev, S. M. Grach, V L Frolov, P. V. KotovAbstract:Abstract Results of systematic study of Stimulated Electromagnetic Emission (SEE) steady state spectrum dependence on the Pump Wave frequency f 0 are presented. Investigations of the HF-Pumped ionosphere were performed at the SURA facility for the frequency range 4.3 f 0 nf ce from n = 4 to 7. The results are based on the data collected during 1996–2004. The main tendencies in a behavior of the most prominent SEE spectral features (their peak and total intensities, and positions in the spectrum) versus f 0 are established and studied in detail. A comparative analysis of peculiarities of different spectral features allows to improve a determination of the electron gyrofrequency in the ionosphere from the SEE spectra, as well as provides a base for deeper understanding nonlinear processes in the Pump-driven upper hybrid turbulence responsible for the SEE generation.
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Experimental Studies of the Effects Observed During the Nonlinear Interaction of Two High-Power Radio Waves in a Magnetoplasma
Radiophysics and Quantum Electronics, 2005Co-Authors: V L Frolov, E. N. Sergeev, B. Thidé, E. A. ShorokhovaAbstract:We present the results of experiments on modification of the ionospheric F region by two high-power (P_eff ≈ 20 MW) O-mode electromagnetic Waves. The experiments were performed at the “Sura” heating facility of the Radiophysical Research Institute (Nizhny Novgorod, Russia) in May 23–27, 1993 at the Pump frequencies near the 4th, 5th, or 6th harmonics of the electron gyrofrequency. Ionospheric perturbations were diagnosed by measuring the stationary spectral characteristics of the stimulated electromagnetic emission (SEE) of the ionospheric plasma. We determine the features of variation in the spectral characteristics of particular SEE components during the simultaneous heating of the ionospheric plasma by two radio Waves in comparison with the case of a monochromatic Pump Wave. We observed the effect of enhanced generation of the broad up-shifted maximum (BUM) by the higher-frequency Pump Wave. This is accompanied by strong suppression of the BUM induced by the lower-frequency Pump Wave. It is shown that the effects observed during the two-frequency heating of the ionosphere have well pronounced gyroharmonic properties, i.e., depend on both the electron-gyroharmonic number and the frequency detuning of the Pump Waves from a harmonic of the electron gyrofrequency. We also pointed out that a change in the properties of artificial small-scale ionospheric irregularities (striations) excited by high-power radio Waves is not the cause of a change in the properties of the down-shifted maximum and the BUM during the two-frequency modification of the ionospheric plasma. Ways for the further development of these studies are discussed.
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spectral features of stimulated electromagnetic emission measured in the 4 3 9 5 mhz Pump Wave frequency range
Geophysical Research Letters, 2001Co-Authors: V L Frolov, E. N. Sergeev, E N Ermakova, G P Komrakov, P StubbeAbstract:Steady state spectral features of stimulated electromagnetic emissions (SEEs) for their major emission components (DM, NC, BC, BUM, and BUS) are studied in a wide Pump Wave frequency range, from 4.3 to 9.5 MHz, i.e., from slightly above the 3rd to slightly above the 7th gyroharmonic frequency. Based on these systematic experimental data, new peculiarities in the behaviour of the SEE intensity and of the spectral properties, in relation to the gyroharmonic mode number, have been found. The experimental results, discussed in the paper, were collected during the years 1996–2000 at the Sura heating facility in Russia by modification of the ionospheric F region, using ordinary mode HF Pump Waves.
T.b. Leyser - One of the best experts on this subject based on the ideXlab platform.
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Stimulated electromagnetic emissions by high-frequency electromagnetic Pumping of the ionospheric plasma
Space Science Reviews, 2001Co-Authors: T.b. LeyserAbstract:A high frequency electromagnetic Pump Wave transmitted into the ionospheric plasma from the ground can stimulate electromagnetic radiation with frequencies around that of the ionospherically reflected Pump Wave. The numerous spectral features of these stimulated electromagnetic emissions (SEE) and their temporal evolution on a wide range of time scales are reviewed and related theoretical, numerical, and simulation results are discussed. On long (thermal) time scales the SEE constitutes a self-organization of the ionospheric plasma which depends on the interaction of nonlinear processes in a hierarchy of time scales in response to the electromagnetic Pumping. Particularly, the appearance of the rich SEE spectrum is associated with the slow self-structuring of the plasma density into a spectrum of magnetic field-aligned density striations. The dependence of the SEE on electron gyroharmonic effects and the presence of density striations suggests that the existence of a magnetic field in the plasma is important for plasma turbulence to dissipate into non-thermal electromagnetic radiation during the long time quasi-stationary state of the turbulence evolution.
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Stimulated electromagnetic emissions by high-frequency electromagnetic Pumping of the ionospheric plasma
Space Science Reviews, 2001Co-Authors: T.b. LeyserAbstract:A high frequency electromagnetic Pump Wave transmitted into the ionospheric plasma from the ground can stimulate electromagnetic radiation with frequencies around that of the ionospherically reflected Pump Wave. The numerous spectral features of these stimulated electromagnetic emissions (SEE) and their temporal evolution on a wide range of time scales are reviewed and related theoretical, numerical, and simulation results are discussed. On long (thermal) time scales the SEE constitutes a self-organization of the ionospheric plasma which depends on the interaction of nonlinear processes in a hierarchy of time scales in response to the electromagnetic Pumping. Particularly, the appearance of the rich SEE spectrum is associated with the slow self-structuring of the plasma density into a spectrum of magnetic field-aligned density striations. The dependence of the SEE on electron gyroharmonic effects and the presence of density striations suggests that the existence of a magnetic field in the plasma is important for plasma turbulence to dissipate into non-thermal electromagnetic radiation during the long time quasi-stationary state of the turbulence evolution.
J P Monchalin - One of the best experts on this subject based on the ideXlab platform.
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detection of ultrasonic motion of a scattering surface by two Wave mixing in a photorefractive gaas crystal
Applied Physics Letters, 1994Co-Authors: Alain Blouin, J P MonchalinAbstract:The performance of an interferometric system based on two‐Wave mixing at 1.06 μm in undoped GaAs crystal, for the remote detection of transient motion of a scattering surface, is described. In this system, the Wave scattered by the surface is mixed inside the photorefractive crystal with a Pump Wave directly derived from the laser to provide the reference Wave of the interferometer. The system shows several features appropriate to industrial applications, although its sensitivity is less than passive interferometric systems of the confocal Fabry–Perot type presently in use, except in the low frequency range (below 1 MHz).
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broadband optical detection of ultrasound by two Wave mixing in a photorefractive crystal
Applied Physics Letters, 1991Co-Authors: R K Ing, J P MonchalinAbstract:A method which allows broadband (from typically 1 KHz) optical detection of ultrasound with large light gathering from a scattering surface is presented. The Wave scattered by the surface is mixed inside a BaTiO3 photorefractive crystal with a Pump Wave directly derived from the laser to provide a sideband‐free reference Wave. A polarization configuration which provides sensitive and linear ultrasonic displacement detection is described. This method is demonstrated by detecting laser generated ultrasound.
