Spectra of Stimulated Electromagnetic Emission of the Ionosphere Upon Sweeping of the Pump Wave Frequency Near Gyroharmonics. I. Experimental Results

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. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 6, pp. 461–476, June 2008.     

Features of Excitation of Stimulated Electromagnetic Emission of the Ionosphere Modified by an Oblique High-Power Radio Wave

We present the results of measuring the characteristics of the stimulated electromagnetic emission (SEE) of the ionosphere with variation in the zenith angle of a pump beam of high-power O-mode radio waves in the geomagnetic-meridian plane. The experiments were performed at the midlatitude heating facility “Sura.” It is established that the maximum intensity of the DM and BC components of SEE is observed for southward inclination angles θ ≈ 8°--12° of the antenna beam, for which the most intense generation of artificial small-scale ionospheric irregularities also takes place. Based on the results of measurements near the fourth and fifth harmonics of the electron gyrofrequency, it is found that the first component of the BUM (BUM-1) is generated only when the pump wave reaches the plasma-resonance region. This allows one to assume that, unlike the second component of the BUM (BUM-2), whose generation is determined by development of instability in the upper-hybrid resonance region, the BUM-1 generation mechanism should be related to processes of interaction between a high-power radio wave and the plasma in the plasma-resonance region. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 9, pp. 743–756, September 2005.     

Method for Studying the Dynamics of Fast Frequency Sweeping Events in the Spectra of Non-Thermal Electromagnetic Plasma Emission

Radiophysics and Quantum Electronics - We developed an algorithm for processing of the dynamic spectra of plasma emission, which makes it possible to extract chirped elements with both increasing...     

Analyzing the Processes of Excitation and Decay of Plasma Turbulence near the Fifth Electron Gyroharmonic using Stimulated Electromagnetic Emission of the Ionosphere

We present the results concerning the dynamics of stimulated electromagnetic emission (SEE) in the vicinity of the 5th electron gyroharmonic in the ionospheric-modification experiment. Measurements of the dynamic characteristics of different SEE features were performed at the Sura heating facility (Radiophysical Research Institute (NIRFI), Nizhny Novgorod) with the use of specialized equipment of the Swedish Institute of Space Physics, Uppsala Division (IRFU) designed for signal spectral analysis with a high temporal-frequency resolution. Based on the measurements performed, we analyzed the following features of nonstationary HF plasma turbulence: the competition between excitation of the Langmuir and upper-hybrid plasma modes for different values of mismatch between the pump frequency and the gyroharmonic, the fine structure of nonstationary energy redistribution over the turbulence spectrum during its excitation and relaxation, and the appearance of anomalously strong collisionless dissipation of turbulence energy with increasing pump duration. Possible mechanisms of the observed phenomena are discussed.     

基于氧气A波段发射谱线临近空间大气温度的反演及分析

基于氧气A波段的临边辐射强度模拟数据对临近空间高度（60～110 km）的大气温度反演进行了研究及结果分析。首先, 基于正演模型分别模拟了无噪声和加入噪声情况下的临边辐射强度模拟值,基于这两种模拟数据分别进行了临近空间大气温度反演,并对氧气A波段中的所有谱线的反演结果进行了分析,确定了氧气A波段各谱线权函数变化规律可作为温度观测的判断依据。温度通过影响线强和自吸收两部分来影响辐射强度,且温度对它们的影响正好相反,权函数就是用来表示温度对辐射强度影响大小的函数,而反演结果的差距可从其权函数中得到规律。在无噪声情况下,当温度对自吸收的影响小于对线强的影响时,权函数未发生正负翻转,温度反演精度较高,平均反演偏差为4.1 K;当温度对自吸收的影响大于对线强的影响时（主要位于60～80 km高度）,权函数发生正负翻转,原因是自吸收降低了辐射强度对温度的灵敏度,此时温度的反演精度较差,平均反演偏差达到34.9 K。此外,在有噪声的情况下,强线比弱线的抗干扰能力更强,反演精度更高,在实际观测中也更适合用于温度的反演,所以线强的强弱也是谱线选择的另一个重要的依据。基于辐射弱线, 进一步通过人为提高信噪比来分析辐射强度对反演精度的影响,结果表明：辐射越强,信噪比越大,温度的反演精度越高,反之则越低。当气辉谱线线强达到10-26时, 也可以用于80 km以上的温度反演并获得较好的反演结果, 反演精度<5 K。     

Nonlinear Evolution of a Gaussian Wave Perturbation in the Presence of a High Power Electromagnetic Plane Wave in the F Region Ionosphere

The interaction of a high power electromagnetic plane wave of uniform intensity with a weak electromagnetic Gaussian wave has been studies analytically. The two waves propagate vertically with almost the same frequency in the F region ionosphre. It is seen that the Gaussian wave acquires an oscillatory structure due to the nonlinear coupling of the strong plane wave and the weak Gaussian wave and the amplitude of these fluctuations grows with height. The growth, however, occurs only above a certain altitude z₀, which is determined by the plasma and wave parameters.     

Evolution of Wave Disturbances in the Upper Ionosphere. Part III

This paper continues our studies of propagation of plasma-density disturbances in the upper ionosphere. The frequency dependence of the disturbance amplification is considered. Some phenomena found by modeling of the propagation are pointed out and explained. The problem is analyzed using the geometrical-optics and dispersion-equation methods. Physical interpretation of the modeling results is presented.     

Emission Spectrum and Charged-Particle Trajectory in the Field of an Inhomogeneous Electromagnetic Wave

Doklady Physics - By the example of an inhomogeneous electromagnetic wave formed by the superposition of two plane monochromatic electromagnetic waves, which are arbitrarily directed relative to...     

On the Theory of Stimulated Brillouin Scattering in Plasma with Two-Dimensional Localization and Inhomogeneity of the Pump Wave

Russian Physics Journal - The problem of Mandelstam-Brillouin stimulated scattering in homogeneous and inhomogeneous plasmas is discussed in an approximation of strong dissipation of sound waves,...     

Coherence Volume of an Optical Wave Field with Broad Frequency and Angular Spectra

We consider the sizes of a region in a three-dimensional space in which an optical wave field excites mutually coherent perturbations. We discuss the conditions under which the length of this region along the direction of propagation of the wave field and, correspondingly, its volume are determined either by the width of the frequency spectrum of the field or by the width of its angular spectrum, or by the parameters of these spectra simultaneously. We obtain expressions for estimating extremely small values of the coherence volume of the fields with a broad frequency spectrum and an extremely broad angular spectrum. Using the notion of instantaneous speckle-modulation of the wave field, we give a physical interpretation to the occurrence of a limited coherence volume of the field. The length of the spatiotemporal coherence region in which mutually coherent perturbations occur at different times is determined. The coherence volume of a wave field that illuminates an object in high-resolution microscopy with frequency broadband light is considered. The conditions for the dominant influence of the angular or frequency spectra on the longitudinal length of the coherence region are given, and the conditions for the influence of the frequency spectrum width on the transverse coherence of the wave field are examined. We show that, when using fields with broad and ultrabroad spectra in high-resolution microscopy, this influence should be taken into account.     

用近红外光谱分析法测定汽油辛烷值

用近红外光谱技术测定汽油辛烷值,在高精度分光光度计上测得１２个汽油标准样品和４个未知样品的近红外区吸收光谱,建立多元统计分析模型,用逐步回归法和偏最小二乘法对模型进行校准,并将其用于未知样品的预估分析,辛烷值的分析精度达到≤±１．０。     

The Results of Measurements of Features of Artificial Electromagnetic and Plasma Perturbations in the Outer Ionosphere of the Earth Using the DEMETER Satellite

The results of the DEMETER satellite mission for 2005–2010 are summarized. The characteristics of electromagnetic and plasma perturbations induced in the F₂ layer of the Earth’s ionosphere by the highpower HF radio waves from the SURA heating facility are analyzed.     

ZnO薄膜受激发射特性的研究

氧化锌薄膜因其大的激子结合能和强的光发射、激光阈值低和能在高温下工作等优点而成为制备短波长激光、发光二极管等光电子器件的有希望材料。采用激光分子束外延 (L MBE)方法制备了ZnO薄膜。在室温下 ,测量了样品的吸收光谱 ,以及不同光泵浦强度下的发射光谱。从光谱图中可以看出该材料有很好的质量。研究了ZnO薄膜的受激发射特性及机理 ;测量了发射光强与泵浦光强之间的关系 ;比较了较高激发密度下的受激发射、自发发射和激光脉冲的时间特性 ,这些都证实了该发射是受激发射。