共查询到20条相似文献,搜索用时 156 毫秒
1.
不等位电势是霍尔式传感器产生零位误差的主要因素.在霍尔式传感器的直流激励特性实验中霍尔元件处于梯度磁场中,但是磁场强度未知,因此无法确定磁场强度为零的位置.当采用交流激励时,通过调节霍尔元件在磁场中的位置,使输出的最小电势便是不等位电势,此时便可通过补偿桥路进行补偿. 相似文献
2.
Buckland EL 《Optics letters》1999,24(13):872-874
The transverse optical intensity profile in fibers affects the efficiency of acoustic mode excitation by the optical field and the subsequent response of the field to the excited acoustic modes. The magnitude of the electrostrictive nonlinear coefficient for a square-top intensity profile will exceed that of a Gaussian profile by a fact of 2. For current fiber designs the range of values for n(2str) at zero frequency is expected to vary from 0.43 to 0.71x10(-16)cm(2)W(-1) based on mode profile alone. The relative contribution of electrostriction to the total nonlinear response (electrostrictive+Kerr) in fibers increases proportionately as the mode profile flattens. 相似文献
3.
Analytical calculation in the first order of smallness shows that the equilibrium shape of a drop in the field of a point charge is axisymmetric about the plane passing through the center of mass of the drop normally to the axis connecting the center of mass with the point charge. Whether the equilibrium shape of the drop is stable or not depends on the value of the field parameter, which, in turn, depends on the point charge and the distance to it. There is an asymptotic value of the critical parameter above which all modes become unstable. In the field of the point charge, the mode coupling grows; that is, a mode excited at the zero time generates oscillations of the six nearest modes with amplitudes proportional to that of the initially excited mode. If the initially excited mode loses stability, all the modes coupled with it also become unstable. The surface instability of the drop also develops when the initially excited mode is stable but at least one of the modes coupled with it is unstable. 相似文献
4.
One investigates the influence of thermally excited collective modes in incommensurate systems on the temperature dependence of hyperfine interactions. The observed hyperfine fields are reduced by a temperature-dependent Debye-Waller factor and the hyperfine field amplitude can eventually decrease to zero well below the transition temperature. 相似文献
5.
研究了脉冲激发下单个半导体量子点中单光子发射的统计特性.在旋转波近似条件下,由系统粒子数演化主方程并结合量子回归理论推导了二阶相关函数的运动方程,利用此方程讨论了二阶相关函数随输入脉冲面积的关系.在窄脉冲宽度的脉冲激发下,单光子的发射概率p和效率η都随着强度的增强而产生振荡.研究表明,采用窄脉冲宽度,当输入脉冲面积在π附近时可以得到较高的单光子发射效率.
关键词:
半导体量子点
单光子发射
三能级系统 相似文献
6.
Interaction between forward bulk magnetostatic waves propagating in a structure consisting of two planar films separated by a nonmagnetic spacer is studied. When two modes are excited in the structure, a phase mismatch between them produces symmetric, asymmetric, and “forked” beats of the amplitudes of the magnetically coupled modes. It is shown that the parameters of the beats can be controlled by varying the magnetic field intensity and ration between the initial amplitudes of the modes excited in the structure. 相似文献
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采用三维时域有限差分法(FDTD),模拟计算了光子扫描隧道显微镜(PSTM)系统中的介质和银质金属样品在不同偏振模式光源下的近场强度分布。使用介质小样品检验探针性能,在探针不同位置计算得到了相似的近场强度分布图,说明编写的程序是可信的。给出了等高扫描时p偏振和s偏振条件下,“PSTM”字样介质样品和银质金属样品上方5nm处的近场强度分布图,结果显示:对介质样品,p偏振波能较好的反映样品的形貌,这是由入射电场的方向决定的;银质金属有表面增强作用,对不同偏振波均能在某种程度上反映样品的形貌,仍有待近一步的研究。 相似文献
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Effect of atomic initial phase difference on spontaneous emission of an atom embedded in photonic crystal 下载免费PDF全文
<正>We investigate the effect of initial phase difference between the two excited states of a V-type three-level atom on its steady state behaviour of spontaneous emission.A modified density of modes is introduced to calculate the spontaneous emission spectra in photonic crystal.Spectra in free space are also shown to compare with that in photonic crystal with different relative positions of the excited levels from upper band-edge frequency.It is found that the initial phase difference plays an important role in the quantum interference property between the two decay channels.For a zero initial phase,destructive property is presented in the spectra.With the increase of initial phase difference,quantum interference between the two decay channels from upper levels to ground level turns to be constructive.Furthermore, we give an interpretation for the property of these spectra. 相似文献
10.
The excitation of low frequency modes of oscillations in a magnetized bi-ion or dusty plasma with parametric pumping of the
magnetic field is analysed. The equation of motion governing the perturbed plasma is derived and parametrically excited transverse
modes propagating along the magnetic field are found. With multiple ion species or charged dust present, a number of different
circularly polarized modes can be excited. The stability of these modes is investigated as a function of the plasma parameters.
The modulational instabilities of large amplitude normal modes, modified by the extra ion species or dust and propagating
along the magnetic field, are also investigated
Article presented at the International Conference on the Frontiers of Plasma Physics and Technology, 9–14 December 2002, Bangalore,
India. 相似文献
11.
以6-31G*为基组,采用密度泛函PBE0方法研究了不同外电场(0—0.060 a.u.)对硼球烯B_(40)的基态几何结构、电荷分布、能量、电偶极矩、能隙、红外及拉曼光谱特性的影响;继而采用含时的TD-PBE0方法研究了硼球烯B_(40)在外电场下的电子光谱.研究结果表明:外电场的加入导致分子对称性降低,当电场从0 a.u.变化到0.060 a.u.时,偶极矩逐渐增加,体系总能量和能隙一直减小;外电场的加入将改变红外和拉曼光谱特征,如谐振频率的移动以及红外和拉曼峰的增强或减弱;外电场对硼球烯B_(40)的电子光谱影响较大,当电场从0 a.u.变化到0.060 a.u.时,电子光谱发生红移,同时对振子强度有很大影响,原来振子强度最强的激发态变弱或成为禁阻跃迁,而原来振子强度很弱或禁阻的激发态变得最强.可以通过改变外电场来改变B_(40)的基态性质,以及控制B_(40)的光谱特性. 相似文献
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基于ZnO纳米柱制备及发光实验,建立了ZnO纳米柱的位置和大小都是无序的二维介质结构模型.通过构建增益模型,用时域有限差分法数值模拟了无序介质中频谱特性以及ZnO增益频谱范围内的某一个共振峰对应的波源在无序介质中的光场分布情况,发现了局域模的存在.分四种情况讨论了此局域模的受激辐射与泵浦面积的关系:改变泵浦功率,从左到右依次增加两层ZnO纳米柱泵浦和单独泵浦一个局域区域;泵浦功率一定时,增加泵浦局域区域和非局域区域中ZnO纳米柱个数.结果表明:存在一个临界泵浦功率,当泵浦功率小于临界泵浦功率时,无论泵浦面积多大都不能激发局域模;当泵浦功率大于临界泵浦功率时,对于不同的泵浦功率,局域模被激发所需的临界泵浦面积不同;随着泵浦功率的增加,当泵浦面积一定时,光场相对强度呈递增趋势,当泵浦功率超过临界功率时,光场相对强度急剧上升. 相似文献
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In short waveguides used in integrated optical circuits, the radiation field is often present in the guiding region of a waveguide as well as the guided modes. We show that this can be investigated efficiently by extracting the radiation part from the total input field and simulating its evolution along the waveguide by use of the beam propagation method. The results are presented for a single-mode waveguide and a waveguide junction excited by a Gaussian beam. For a noncentred excitation, a considerable fraction of the radiation power is still in the guiding region after propagation over several tens of micrometres, and can be coupled to guided modes past the junction. 相似文献
16.
Sinatra A 《Physical review letters》2006,97(25):253601
We show that three-level atoms excited by two cavity modes in a Lambda configuration close to electromagnetically induced transparency can produce strongly squeezed bright beams or correlated beams which can be used for quantum nondemolition measurements. The input intensity is the experimental "knob" for tuning the system into a squeezer or a quantum nondemolition device. The quantum correlations become ideal at a critical point characterized by the appearance of a switching behavior in the mean fields intensities. Our predictions, based on a realistic fully quantum three-level model including cavity losses and spontaneous emission, allow direct comparison with future experiments. 相似文献
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Decoding the electron dynamics in high-order harmonic generation from asymmetric molecular ions in elliptically polarized laser fields 下载免费PDF全文
Cai-Ping Zhang 《中国物理 B》2022,31(4):43301-043301
The high-order harmonic generation from an asymmetric molecular ion is theoretically investigated based on the Born-Oppenheimer model with two-dimensional electron dynamics. It is shown that the harmonic intensity changes periodically in elliptically polarized laser fields. The periodical character is ellipticity-dependent. By establishing the physical image, the periodicity of the harmonic intensity can be ascribed to the contributions of the ground state and the excited state. Furthermore, the electron dynamics from different electronic states can be selected via combining the elliptically polarized laser field with a static electric field. The harmonics dominated either by ground state or excited state are emitted once in an optical cycle in the combined laser field. 相似文献
19.
Spatial characteristics of diffracted beams produced by the “fork” holograms from incident circular Laguerre-Gaussian modes are studied theoretically. The complex amplitude distribution of a diffracted beam is described by models of the Kummer beam or of the hypergeometric-Gaussian beam. Physically, in most cases its structure is formed under the influence of the divergent spherical wave originating from the discontinuity caused by the hologram’s groove bifurcation. Presence of this wave is manifested by the ripple structure in the near-field beam pattern and by the power-law amplitude decay at the beam periphery. Conditions when the divergent wave is not excited are discussed.The diffracted beam carries a screw wavefront dislocation (optical vortex) whose order equals to algebraic sum of the incident beam azimuthal index and the topological charge of the singularity imparted by the hologram. The input beam singularity can be healed when the above sum is zero. In such cases the diffracted beam can provide better energy concentration in the central intensity peak than the Gaussian beam whose initial distribution coincides with the Gaussian envelope of the incident beam. Applications are possible for generation of optical-vortex beams with prescribed properties and for analyzing the optical-vortex beams in problems of information processing. 相似文献
20.
Zhi-Wei GuoDe-Jun Sun 《Physics letters. A》2011,375(36):3191-3195
The optimal response in the Lamb-Oseen vortex is studied by considering the harmonically forced problem with frequency ω. High variance levels are sustained in these systems under periodic forcing. In the axisymmetric case n=0, the response is the largest when the input frequency is zero. When considering helical perturbations n=1, large response is excited through resonance mechanism at moderate and large wavelengths. At smaller wavelengths, large response is excited by steady forcing. For perturbations with higher azimuthal wavenumbers |n|>1, the magnitudes of the response are smaller than those for helical modes. For given axial wavenumber and input frequency, the response increases rapidly with Re, which points to the significance of energy growth in high-Reynolds-number practical flows. 相似文献