物理专业英语翻译141-149

物理专业英语翻译141-149
物理专业英语翻译
姓名：陈云飞
学号：09027203
页数：141~149
The distance l coh=c* t coh over which a wave travels during the t coh is called the coherence length （or the train length ）. The coherence length is the distance over which a chance change in the phase reach a value of about π。

To obtain an interference pattern by splitting a natural wave into two parts, it is essential that the optical path difference △ be smaller than the coherence length. This requirement limits the number of visible interference fringes observed when using the layout shown in Fig.6.2. An increase in the fringe number m is attended by a growth in the path difference. As a result, the sharpness of fringes becomes poorer and poorer.
一个波在相干时间运动的距离【l coh= c*t coh】被称为相干长度（波列的长度）。

相干长度是一个阶段的机会改变达到约π的值。

以获得通过分裂成两部分的自然波干涉图样的距离，光程差△小于相干长度是必要的。

使用Fig.6.2所示的布局时，这项规定限制可见干扰观察边缘。

附带数m的增加，是表现在增长路径差异。

因此，边缘锐度变得越来越弱
Let us pass over to a consideration of the part of the non-monochromatic nature of light wave. Assume that light consists of a sequence of identical trains of frequency ω。

and duration ζ。

When one train is replaced with another one, the phase experiences disordered changes .As a result, the trains are mutually incoherent. With these assumptions, the duration of a train ζ virtually coincides with the coherence time t coh.
让我们通过光波的非单色性的考虑。

假设光相同频率ω波列序列组成。

期限ζ，当一列波列与另一取代阶段的经验无序的变化，因此，波列是相干的。

有了这些假设，波列ζ的时间几乎恰逢相干时间的相干时间。

In mathematics, the Fourier theorem is proved, according to which any finite and integrable function F(t) can be represented in the form of the sum of an infinite number of harmonic components with a continuously changing frequency: F(t) =∫|A(ω)e iωt dω (6.16)
Expression (6.16) is known as Fourier integral. The function A(ω) inside the integral is the amplitude of the relevant monochromatic component. According to the theory of Fourier integrals, the analytical form of the function A(ω) is determined by the expression
A(w)=2π∫|F(ξ)e(-iωξ)dξ（6.16）
Where ξ is an auxiliary i ntegration variable.
在数学中，傅立叶定理证明，任何有限的和可积函数F（t），可以在无限多的频率不断变化的谐波成分的总和形式表示：
F（t）=∫|F（ω）e iωt dω（6.16）
表达（6.16）被称为傅立叶积分。

函数内的积分（ω）是有关的单色成分的振幅。

根据傅立叶积分，函数A（ω）的分析形式的理论是表达式
A（ω）=2πF（ξ）e Iωξdξ
其中ξ是一个辅助的一体化变量。

A graph of the real part of this function is given in Fig.6.4.
波形图
Outside the interval from –φ/2 to +φ/2, the function F(t) is zero. Therefore, expression (6.17) determining the amplitude of the harmonic components has the form
A(ω)=2π∫【A0exp(iω0ξ)】exp(-iωξ)dξ
A graph of function (6.18 ) is shown in Fig.6.5. A glance at the figure shows that the intensity of the components whose frequencies are within the interval of width △
w=2π/φ considerably exceeds the intensity of the remaining components . This circumstance allows us to relate the duration of a train φ to the effective frequency range △ωof a Fourier spectrum:
φ =2π/△ω=1/△v
Identifying φ with the coherence time, we arrive at the relation
t coh~1/△v
(The sign ~ stands for ”equal to in the order of magnitude”)在Fig.6.5所示的函数曲线图（6.18）。

一个一目了然的数字显示，频率的宽度间隔内的元件，其强度△W =2π/φ大大超过其余部分的强度。

此情况下，使我们能够与波列φ期间△ω的傅立叶频谱的有效频率范围：
φ=2π/△ω= 1 /△v
φ识别与相干时间，我们到达的关系
t coh?1 /△v
（符号?表示“等于量级”）
It can be seen from expression (6.19) that the broader the
interval of frequencies present in a given light wave, the smaller is the coherence time of this wave.
可以看出，从更广泛的间隔在一个给定的光波的频率，规模较小的，是这一波的相干时间的表达（6.19）。

△m=±m λ0~~±m λ
When this path difference reaches values of the order of the coherence-length, the fringes become indistinguishable .Consequently, the extreme interference order observed is determined by the condition
Spatial Coherence. According to the equation k=ω/v=nω/c, scattering of the
frequencies △ω results in scattering of the values of k. We have established that the
temporal coherence is determined by the value of △ω. Consequently, the temporal coherence is associated with scattering of the value of the magnitude of the wave vector K. Spatial coherence is associated with scattering of the directions of the vector K that is characterized by the quantity △e k.
空间相干性。

根据方程K=ω/ V=nω/c，散射的频率在散射光值△ω结果我们已经建立了时间相干性△ω的值决定。

因此，时间相干性与散射载体k.空间相干性是相关联的特点就是由数量△e k矢量k方向散射波的幅度值。

The setting up at a certain point of space of oscillations
produced by waves with different values of e k is possible if these waves are emitted by different sections if an extended (not a point) light source. Let us assume for simplicity’s sake that the source has the form of a disk visible from a given point at the angle φ。

It can be seen from Fig.6.6 that the angle φ characterizes the interval confining the unit vector e k. We shall consider that this angle is small.
设置在不同的价值观与EK波产生的振荡空间的某一点是可能的，如果这些波是由不同的部分，如果一个扩展（不是点）光源发出的。

让我们假设为简单起见，源磁盘从一个角度φ点可见的形式，可以看到从Fig.6.6，角度φ间隔围的单位向量e k的特点。

我们应考虑这个小角度。

The zero-order maximum “M’’” produced by the wave arriving from section “O’’”is displaced in the opposite direction from the middle of the screen over the distance X’’ equal to X’. The zero-order maximum from the other sections of the source will be between the maxima” M’” and”M’’”.
零阶最大的M“从第0抵达波产生的”流离失所者在向相反的方向，在距离X“X”等于屏幕中间。

从零阶的最大源的其他部分在最大值M“和”M''之间
Or
We have omitted the factor 2 when passing over from expression (6.22) to (6.24).
X'<△X，即
和△t coh=∞），通过狭缝的表面是一种波，并在这种表面的所有点的波动将同步
发生。

我们已经确定，当△v≠0和波源尺寸（φ≠0），在表面距离D>λ/φ点的波不相干。

We shall call a surface which could be a wave one if source were monochromatic a pseudowave surface for brevity. We could satisfy condition(6.24) by reducing the distance d between this slits, i.e.by taking closer points of the pseudo wave surface. Consequently, oscillations produced by a wave at adequately close points of a pseudo wave surface are coherent. Such coherence is called spatial.
如果源单色一个简洁pseudowave的表面，这可能是一个波之一，我们将调用一个表面。

我们可以减少这个狭缝之间的距离d满足条件（6.24），ieby
伪波面接近点。

因此，在充分接近伪波面点波产生的振荡是一致的。

这种相干性是称为空间。

Thus, the phase of an oscillation changes chaotically when passing from one point of a pseudowave surface to another. Let us introduce the distance ρcoh
， upon displacement by which along a pseudowave surface a random change in the
phase reaches a value of about π. Oscillations at two points of a pesudowave surface spaced apart at a distance less than ρcoh will be approximately coherent. The distance ρcoh is called the spatial coherence length or the coherence radius. It can be seen from expression (6.25) that
The entire space occupied by a wave can be divided into parts in each of which the wave approximately retains coherence. The volume of such a part of space, called the coherence volume, in its order of magnitude equals the products of temporal coherence length and the area of a circle of radius ρcoh。

波占用整个空间可以分为多个相干部分。

这样一个空间的一部分，在其量级等于时间相干长度和半径为ρcoh的圆的面积的区域内被称为相干量。

The spatial coherence of a light wave near the surface of the heated body emitting it is restricted by a value of ρcoh of only a few wavelengths. With an increasing distance from the source, the degree of spatial coherence grows. The radiation of a laser has an enormous temporal and spatial coherence. At the outlet opening of a laser, spatial coherence is observed throughout the entire cross section of the light beam.
附近的加热体发光，它是由限制的只有少数几个波长的值ρcoh表面光波的空间相干性。

从源距离的增加，空间相干度的增长。

激光的辐射有一个巨大的时间和空间的连贯性。

空间相干性激光的出风口，整个光束的整个横截面观察。

It would seem possible to observe interference by passing light propagating from an arbitrary source through two slits in an opaque screen. With a small spatial coherence of the wave falling on the slits, however, the beams of light passing through then will be incoherent, and an interference pattern will be absent. The English scientist Thomas Young (1772-1829) in 1802 obtained interference from two slits by increasing the spatial coherence of the light falling on the slits. Young achieved such an increase by first passing the light through a small aperture in an opaque
screen. This light was used to illuminate the slits in a second opaque screen. Thus, for the first time in history, Young observed the interference of light waves and determined the length of these waves.
这似乎可以观察在一个不透明的屏幕上，通过两个狭缝光传播从任意源的干扰。

然而，随着一个小狭缝的下降波的空间相干性，光线穿过梁然后将相干，和一个干涉图样将缺席。

英国科学家托马斯杨（1772年至1829年）在1802年通过把单个波阵面增加两个狭缝的获得两个波阵面来获得光的空间相干波。

杨在一个不透明的屏幕上，首先通过小光圈光取得这样的增幅。

此灯是用
来在第二个不透明屏幕照亮狭缝。

因此，杨历史上首次观测的光波的干扰，并确定了这些波的长度。

6.3 WAYS OF OBSERVING THE INTERFERENCE OF LIGHT
Let us consider two concrete interference layouts of which one uses reflection for splitting a light wave into two parts, and the other refraction of light
Fresnel’s Double Mirror. Two plane contacting mirrors OM and ON are arranged so that their reflecting surfaces from an obtuse angle close to π(Fig.6.8). Hence, the angle φ in the figure is very small. A straight light source S(for example, a narrow luminous slit) is placed parallel to the line of intersection of the mirrors
O(perpendicular to the plane of the drawing) at a distance r from it . The mirrors reflect two cylindrical coherent waves onto screen Sc. They propagate as if they were emitted by virtual sources S1 and S2 , Opaque screen S c1 prevents the direct propagation of the light from source S to screen S c.
6.3 观察光干涉的方法
让我们考虑两个具体的相干关系，其中之一使用分裂反射光波分为两个部分，和其他折射光
菲涅耳双面镜。

两平面接触镜OM和ON安排，使他们反映，从一个钝角接近π（Fig.6.8）的表面。

因此，图中的角φ是非常小的的。

一个直光源S（例如，一个狭窄的光缝）平行放置行的镜子为O（绘图平面垂直）从它的距离r
的交点。

镜子反映到屏幕SC两个圆柱相干波。

类似虚拟源S1和S2τ发射出光波，不透明的屏幕S C1阻止从源S的光直接传播到屏幕S C。

Ray OQ is reflection of ray SO from mirror OM, and ray OP is the reflection of ray SO from mirror ON. It is easy to see that the angle between rays OP and OQ is 2φ。

Since S and S1, are symmetrical relative to OM, the length of segment OS1 equals OS, i.e.r. Similar reasoning leads to the same results for segment OS2. Thus, the distance between sources S1 and S2 is
d=2rsinφ≈2rφ
Inspection of Fig.6.8 shows t hat α=r cosφ≈r. Hence,
l=r+b
Where b is distance from the line of intersection of the mirrors O to screen S c. Using the values of “d” and “l” we have found in Eq.(6.10), we obtain the width of an interference fringe
△x=(r+b) λ/2rφ
The region of wave overlapping PQ has a length of 2b tan φ≈ 2bφ. Dividing this
length by the width of a fringe △x, we find the maximum number of interference fringes that can be observed with the aid of Fresnel’s double mirror at the given parameters of a layout:图形
N=4brφ2/λ(r+b)
For all these fringes to be visible indeed, it is essential that
N/2 be not greater than M-extra determined by expression.(6.22).
PQ的地区波重叠有2btanφ≈2bφ。

边缘的宽度除以长度△x，我们通过菲涅耳双镜的，可以找到在给定的参数观察的相干条纹的最大数量：
图形
N =4BRφ2/λ（r+ b）。