随机电报过程引起的光失相的计算机模拟

动态微扰可以引起跃迁频率发生变化,产生光谱扩散,我们用Monte Carlo法模拟了由于频率变化引起的自由感应衰减和光子回波衰减。模拟的结果表明,衰减的线形只和频率变化与跳变速率的比值有关,根据它的不同取值,自由感应衰减呈指数和非指数形式,光子回波强度为exp[-(4τ/tm)^x],x取值从1到3。我们还定性地讨论了红宝石中光子回波的非指数衰减。     

强磁场下顺磁掺杂离子的光谱扩散

采用一种简明的解析方法从纯粹频域的角度讨论强磁场下顺磁离子掺杂体系的光谱扩散过程。一般说来光谱扩散遵循[1-exp(-WT_w)]^x的形式,W是跳变速率,T_w为等待时间。在不存在冷冻核时,对于频域和时域x分别为1/2和1。考虑到冷冻核效应,光谱扩散的速率将近似地以因子(ω_eff/ω₀)²减慢,这里ω₀是描述冷冻核的特征频率。当冷冻核充分大时,频域和时域的光谱扩散的行为趋于一致x≈0.22。     

Grover量子搜索算法的一般化多相位匹配

一个量子系统将不可避免地受到不可预知的微扰影响,据此断定文献中的Grover量子搜索算法的实验实现是在三维复子空间中完成的.同时证明在二维复子空间中,对任意给定的初始态|γ0＞=cosβ0| α＞+sinβ0eiζ|β＞(β0是较小的正实数,ζ是任意的一个实数),存在解集Fj={(θj,θj-1,…,θ1),(φj,φj-1,…,φ1)}(整数j≥2)使得目标态能以100％的最大成功概率找到,其中相位旋转角θj和φl是不为2k’π的实数(1≤l≤j,k’为任意整数).如果只要求目标态以较高的成功概率找到,那么当一个无序数据库中目标态和非目标态的总个数足够大时,对于相对较小的正整数j,解集Fj可表示为j∑l=1θl=j∑l=1φl的形式.     

LiNbO_3在反常色散区光学常数的测定

我们用170SX傅里叶变换红外光谱仪,测量了LiNbO_3在30cm~(-1)～2800cm~(-1)波段内的反射光谱。应用Kramers-Kronig关系的积分形式,快速而准确地计算出LiNbO_3在同一波段内的各种光学常数的谱图。由此,可直接得到A_1模和E模的横频率ω_T、纵频率ω_L和高频介电常数ε_∞。计算了振子强度。讨论了振子间的相互耦合作用。并认为670cm~(-1)模就是E模的一个基频。     

相速度、群速度与超光速问题

相对论中指出了:真空中的光速c是信号传播的极限速度.然而.在一些力学、电磁学和光学书里,却常常看到相速度、群速度出现超光速的情况,这是否与相对论的理论相矛盾呢? 相速度、群速度都是用来描述波的传播的物理量.由于在实际情况中,无论是单色光源或者调谐锐度很高的无线电发射机,所发射的波总有一定的频率宽度,形成一个波列.因此,我们研究波的传播时,必须考察这一波列中所有单色波的合成波,它可以写作此频率区间 内所有各波的一个积分:由于ω=ω(K),ω0对应K0,△ω对应△K,将ω(K)在ω0附近展开:略去(2)式中的高次项,代入(1)式;由于A(K…     

关于等离子体横越磁场的非经典扩散

一、引言 处于外磁场中的等离子体内,荷电粒子横越磁场的扩散除了经典扩散外,无论热平衡或湍动等离子体中均存在非经典增强扩散。如文献[3]研究处于热平衡等离子体中的扩散,指出存在三个区域,当磁场强度B充分弱时,横越磁场的扩散系数D是经典扩散,即D～B~(-2);当ω_(ce)>ω_(pe)时,D则几乎与B无关;而当磁场增强到ω_(ci)>ω_(pi)后,D～B~(-1)。后两种非经典增强扩散的机构是由集体模型,即由热激励的对流模型所主导的。     

弱场中Ba-Sr系统激光感生碰撞过程的理论研究

针对四能级理论模型的第二种极限情况 ,提出了 Ba- Sr激光感生碰撞能量转移系统 ,该系统满足 |ω2 1| |ω4 3|。利用四能级理论模型对该 Ba- Sr系统进行了数值计算 ,并与三能级近似理论模型的计算结果进行了比较。通过比较四能级理论与三能级近似理论模型的计算结果 ,进一步证实了当 |ω2 1| |ω4 3|时 ,四能级理论模型可以过渡为三能级理论模型     

红外反射光谱法测GaAs的光学常数

本文用红外反射光谱,通过反Kramers-Kronig关系计算出不同掺杂浓度n-GaAs晶体的光学常数的谱图。从介电常数的谱图,直接得到了GaAs晶体晶格振动的横频率ω_T、纵频率ω_L、高频介电常数ε_∞、静态介电常数ε_S以及等离子频率ω_P与ω_L的相互耦合频率ω_+、ω-。讨论了载流子浓度对光学常数的影响及ω_P与ω_L的相互耦合作用。其实验谱图值与计算值相一致。     

“光学一题”解答

利用如图所示的迎光矢量分布图,设两块(λ/4)波晶片的快轴都沿x方向,旋转的半波片快轴沿x’方向,且在t 时刻 x’和 x的夹角为 ω’ t,振幅为2A的入射线偏光通过第一块(λ/4)波晶片后的振动方程为这是一个频率为ω的左旋圆偏光.它通过半波片后的振动方程为这是一个频率为(ω一ω’)的右旋圆偏光.当这一右旋偏光通过第二块(λ/4)波晶片后,则出射光的电振动方程为由此可知,出射的是线偏光,其振动方向与入射的相同,振幅也是2A,但频率却由原来的ω变为 容易证明,当某一(λ/4)波晶片转过90°时,人们将获得m+2ω’的线偏光;有时,也可能使出射线偏…     

具有运动边界与含时频率的一类环状非球谐振子模型势的精确解(英文)

在球坐标系中研究了一类具有运动边界与含时频率的环状非球谐振子模型势的Schrdinger方程.应用坐标变换将运动边界转化为固定边界,从而获得了系统的精确波函数.研究表明,系统的角向波函数是一个推广的缔合勒让德多项式,径向波函数可以表示为贝赛耳函数.最后我们简单讨论了指数运动边界和指数含时频率这一特殊情况.     

On the enhancement of the nonlinear frequency transformation in periodic media

It is theoretically shown that an enhancement of the nonlinear frequency transformation in a periodic medium occurs under definite conditions if it is accompanied by light diffraction in this medium. The enhancement of the phase-matched frequency transformation occurs if the harmonic frequency ω approaches the stop band frequency ω_e. In the nondepleted pump approximation the corresponding increase of the harmonic intensity is proportional to ω_e(ω?ω_e)^?1 and is restricted by a quantity proportional to the fourth power of the sample thickness. The formulas for the enhancement of second harmonic generation are presented.     

Fermi-edge singularity in the vicinity of the resonant scattering condition

Fermi-edge absorption theory predicting the spectrum A(ω) ∝ ω(-2δ(0)/π+δ(0)92)/π2) relies on the assumption that scattering phase δ(0) is frequency independent. The dependence of δ(0) on ω becomes crucial near the resonant condition, where the phase changes abruptly by π. In this limit, because of the finite time spent by electron on a resonant level, the scattering is dynamic. We incorporate the finite time delay into the theory, solve the Dyson equation with a modified kernel, and find that, near the resonance, A(ω) behaves as ω(-3/4)|lnω|. Scattering off the core hole becomes resonant in 1D and 2D in the presence of an empty subband above the Fermi level; then a deep hole splits off a level from the bottom of this subband. Fermi-edge absorption in the regime when resonant level transforms into a Kondo peak is discussed.     

Stability and Symmetry-Breaking Bifurcation for the Ground States of a NLS with a δ′ Interaction

We determine and study the ground states of a focusing Schrödinger equation in dimension one with a power nonlinearity |ψ|^2μ ψ and a strong inhomogeneity represented by a singular point perturbation, the so-called (attractive) δ′ interaction, located at the origin. The time-dependent problem turns out to be globally well posed in the subcritical regime, and locally well posed in the supercritical and critical regime in the appropriate energy space. The set of the (nonlinear) ground states is completely determined. For any value of the nonlinearity power, it exhibits a symmetry breaking bifurcation structure as a function of the frequency (i.e., the nonlinear eigenvalue) ω. More precisely, there exists a critical value ω* of the nonlinear eigenvalue ω, such that: if ω₀ <  ω <  ω*, then there is a single ground state and it is an odd function; if ω >  ω* then there exist two non-symmetric ground states. We prove that before bifurcation (i.e., for ω <  ω*) and for any subcritical power, every ground state is orbitally stable. After bifurcation (ω = ω^* + 0), ground states are stable if μ does not exceed a value ${\mu^\star}$ that lies between 2 and 2.5, and become unstable for μ > μ*. Finally, for μ >  2 and ${\omega \gg \omega^*}$ , all ground states are unstable. The branch of odd ground states for ω <  ω* can be continued at any ω >  ω*, obtaining a family of orbitally unstable stationary states. Existence of ground states is proved by variational techniques, and the stability properties of stationary states are investigated by means of the Grillakis-Shatah-Strauss framework, where some non-standard techniques have to be used to establish the needed properties of linearization operators.     

Non-adiabatic transitions for random processes in a two-level system

Non-adiabatic transitions in two-level systems are investigated theoretically for a random time dependence of ?ω, the energy difference, between the levels. We assumed that ω = ω(x) and the coordinate x = x(t) is a random function of time. Diffusion and Poisson processes (both homogeneous and with a source) for x(t) were assumed. The cases of linear crossing terms (ω = γx) and non-linear terms (ω = ω _e exp (- αx) + ω₀) were considered. Values of the non-adiabatic transition probability per unit time were obtained by perturbation theory for ω₁τ _c ? 1 where τ _c is the correlation time and ω₁ is the off-diagonal matrix element.     

ω粒子的辐射衰变

本文由质量的解析延拓得到ω→π+r过程的色散关系,讨论了某些有关不稳定粒子色散关系的问题。在一些简化假设下得到W_ω→π+r/W_ω→3π≈0.35。在η粒子与ω粒子量子数相同的情形下得到W_η→π+r/W_η→3π≈25,在计算中包含了三个π介子成对作用的效应。     

Induction kinetics in 2D electron systems at the Hall plateaus

Specific features of the induction excitation of 2D electron systems at the Hall plateaus are discussed. The corresponding kinetics is shown to have several frequency regimes. In the region ω ? ω_D, where ω_D is the frequency characteristic of the kinetics at the Hall plateaus, an induction-caused variation of electron density follows the magnetic-field variation with time. For the frequencies ω ≤ ω_D, a noticeable relaxation of the electron disturbance appears, and the induction polarization of 2D samples at the Hall plateaus noticeably decreases as compared to the maximum possible polarization. Finally, in the limit ω ≤ ω_slow, where ω_slow corresponds to another characteristic time of the quantum Hall effect, the so-called adiabatic approximation takes place with the 2D system responding to the derivative of magnetic field dH/dt rather than to the magnetic field itself H(t). The results of calculations are compared with the experimental data reported in the literature.     

On the theory of Boson peak in glasses

A universal mechanism of the Boson peak formation in glasses is proposed. The mechanism is based on the concept of interacting quasilocal oscillators. Even in the case of weak interaction, the low-frequency spectrum becomes unstable. Due to anharmonicity, the system undergoes a transition into a new stable configuration. As a result, below some characteristic frequency ω_c, proportional to the typical strength of interaction, the renormalized density of states becomes a universal function of ω with a Boson peak feature; i.e., the reduced density of states g(ω)/ω² has a maximum at a frequency ω_b?ω_c. We derive an analytic form of this function.     

Inverse Monte Carlo solutions for radiative transfer in inhomogeneous media

The inverse Monte Carlo method is used to construct solutions for three radiative transfer inverse problems in which the single scatter albedo, ω, varies within the medium and the scattering is isotropic. The first problem concerns a half space whose single scatter albedo varies exponentially according to ω = ω₀e^?τ/s, where τ is the optical depth, s is known and we seek ω₀; the second problem concerns a two-region slab for which we seek ω for each region. The procedure is also used to construct an approximate solution for a finite, plane-parallel medium whose single scatter albedo varies exponentially by considering the medium to be composed of five regions, each with constant single scatter albedo.