照明技术文件 偏振光仪

THE POLARIS COPE

偏振光仪

© Philips Lighting B.V. 2002 (department I.S.G.T.) All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of Philips Lighting B.V., dept. I.S.G.T. - the Netherlands.

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Subject: The Polaris cope 题目：偏振光仪

Contents 目录

1. Introduction 介绍

2. Some theoretical backgrounds 背景理论 2.1. Polarisation 偏振 2.2. Interference 干涉

2.3. Glass with strain 带应力的玻璃

3. How to adjust the polariscope? 如何调整偏振光仪？ 4. Which information gives the polariscope? 偏振光仪的应用？ 5. Assessment of strain 应力评估

International Support group Glass Technology

玻璃工艺国际支持组

Jan 2003 2003年1月

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1. Introduction 介绍

As explained in the information on Glass properties, the result of heating and cooling down glass can be that strain or stress is generated in the glass (both terms, although not quite the same are usually used interchangeably). It has also been explained that especially the permanent stress can lead to cracks that can damage the product or create a dangerous situation for the customer. Therefore it's important to be able to judge the stress after a product has been made.

我们在玻璃特性中介绍过，玻璃的加热和冷却会在玻璃中形成压力或张力（两种力虽然不同但经常互换）我们已经介绍过尤其是永久应力会产生破裂损坏产品或对顾客造成危险，因此在产品完成后对其应力进行分析是很重要的。

There are basically two ways to get information in relation to strain: 有两种基本的方法对应力进行分析：

1) Mathematical: with special microscopes measurements are made and via mathematical methods a value for the strain can be calculated. These methods are often used in labs and will not be discussed in this introduction.

机械方法：使用专门的显微镜测量，通过数学方法计算出应力值，这些方法经常在实验室中使用，我们在此不做讨论。

2) By comparison: with the polariscope one can see a colour pattern in the product.

By comparing this with so-called \"limit\" samples one can get an idea about the acceptability of a certain strain pattern. This method is often used in the factories and will therefore further be explained in this introduction.

作为比较：使用可以看出产品中颜色形式的偏振光仪。通过与样品进行比较可以知道什么是正确的应力形式，这种方法经常在工厂中使用，因此我们对此将进行详细讨论。

It is obvious that a lot of experience is required to be able to interpret the pictures which one can see under the polariscope, on the other hand as strain is so important we are of the opinion that a basic knowledge in relation to the polariscope and its use is mandatory as part of this course. During the course several examples will be used to demonstrate the usefulness of working with the polariscope. A sketch of a polariscope is shown on the next page (fig. 2).

很显然，能够分辩偏振光仪下的图样需要很多的经验，然而我们已经了解了应力的重要性，这个课程就是试图介绍一些关于偏振光仪的基础知识和使用方法。

在课程中我们将结合一些例子来说明使用偏振光仪的有益之处。下一页中我们展示了偏振光仪的草图。（图2）

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1. Rudolph instruments 2. Philips. 3. Herbert Arnold.

Fig. 2 The polariscope.

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2. Some theoretical backgrounds 背景知识

Although it is not our intention to explain in all details the theoretical backgrounds of the polariscope we will shortly indicate the basic laws of physics which are involved to understand the working of the polariscope.

我们不想在此介绍所有关于偏振光仪的背景知识，知识简单地介绍一些难于理解偏振光仪工作的基础的物理原理。 2.1 Polarization 偏振

Normal \"un polarized\" light vibrates in all directions perpendicular to the direction of the light beam. The human eye is not sensitive for this. However in the same way as a colour can be separated from a white beam by means of a colour filter, a direction of vibration can be filtered out by a polarizing filter. The result is a light beam with only one vibration direction and the light is called polarized light. An illustration is given below (fig 2). The vibration directions can be drawn as vectors.

一般的非偏振光在与光束垂直的所有方向上振动，肉眼是观测不到的，同白光能被彩色虑光镜分成各种色光一样，振动的方向也能被偏振虑镜滤出，这样光束只剩下一个振动方向，这种光即为偏振光，图2对此进行了说明（图2） 振动描述为矢量。

Fig. 2 Polarized light 偏振光

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Each vector can be resolved in a component parallel to the polarization direction of the filter and a component perpendicular to this direction. As the length of the projection is a measure for the amount of light in that direction one can understand that half the \"amount of light\" is lost in the filter.

The reason is that all the components perpendicular to the filter direction are \"blocked\" by the filter and therefore do not get through, while the components parallel to the direction are completely transferred! Example:

每个矢量能分解成与滤镜偏振方向平行的分量和垂直的分量，测量慢射的长度可以得出该方向上光的数量，分析以后可知有一半的光的数量在滤镜中消失了。

原因是所有垂直方向的光都被滤镜阻挡而不能够通过，而同时平行方向上的光则可以完全通过。例如：

Fig. 3 Example of vector components. In our example a and b1 are blocked while b2 and c are transferred. Let us now consider a few situations:

1) When two polarizing filters are put in a way that the polarizing directions are perpendicular to each other the light beam will be completely extinguished as can be seen in fig.3. In the first filter one half of the light will be lost while in the second filter the other half will be lost. (Fig. 4) 本例中a和b1被阻挡了，而c和b2则通过了。 现在我们分析一些情况：

1）当两只偏振滤镜垂直排列，光线就完全消失了，如图3所示，在第一个滤镜损失了一半的光，而在第二个滤镜则损失了剩余的光。（图4）

Fig. 4. 6

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2) When the two filters are not perpendicular to each other but under an angle a certain amount of light will be seen as can be understand by resolving the vectors in the same way as explained before (fig. 5).

当两只滤镜不是垂直而是成一个角度排列时，可以观察到一定数量的光，如同前面解释过的矢量分解的原理一样。（图5）

Fig. 5. 3) If we put two filters perpendicular to each other but another one under an angle in between, a certain reduced light output can also be seen. This may at first sight be unexpected but can be easily understood by looking again to the vector resolving as can be seen in fig. 6.

如果我们将两只滤镜垂直排列而将另一只滤镜成一个角度放置在中间，也可以观察到一定量减少的光的输出，刚开始可能不能理解，但再参阅一下图6所示的矢量的分解。

Fig. 6.

Please note that the maximum light output will be achieved when the middle polarizer is at an angle of 45o as can be deducted from the vector projections.

请注意当中间的滤镜成45 o角放置的时候，如同减少发射的矢量的道理一样，而达到最大的光的输出。

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(1) Ι = 45o (2) Ι > 45o (3) Ι < 45o result a3 smaller result a3 smaller

than in (1) than in (1)

结果a3变小 结果a3变小 同（1）相比 同（1）相比

a = polarized through P 通过P的偏振光

a1 = component blocked by filter F 被滤镜F阻挡的分量 a2 = component through F 通过F的分量

a3 = component through A 通过A的分量

Fig. 7. 2.2. Interference 干涉

Interference is the phenomena that two waves in the same plane are influencing each other where the net result can be re-inforcement or extinguishing, depending whether the two waves are in phase or in opposite phase to each other. See below:

干涉是一种现象，两列波在同一平面内相互影响，在哪里衰减，在那里增强最终结果取决于两列波相互的相位叠加或抵挡，如下所示：

Fig. 8. Interference.

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One can compare this with two people pulling a rope to move an object. When they pull in the same direction the object will be pulled with double force (= reinforcement); when they pull in opposite direction the object will not move (= extinguishing).

我们可以用两个人拉一根绳子移动物体来打比方，当他们朝向一个方向拉时，物体将受到两倍的力拉（增强），当朝不同的方向拉时，物体将不动（抵消）。

This means that 2 light rays with the same wavelength, vibrating in the same plane (i.e. after polarization!), but out of phase, will interfere. Depending on the phase shift the light output will vary between twice as much light and complete darkness.

这意味着两束相同波长的光在同一平面内振动（例如偏振后），但仍超出相位，就将发生干涉，根据相位差输出光将在两倍亮和完全黑之间。 2.3. Glass with strain 应力玻璃

Strain-free glass is \"isotropic\all directions. Strain however makes the glass \"anisotropic\".

A ray of polarized light will be broken into two other polarized rays vibrating at right angles to each other. For a simple axial tensile or compressive strain one ray always vibrates in the plane which includes the axis of the stress and its velocity varies with the inclination of the incident light (for this unusual behaviour this ray is called the extraordinary ray \"e\"). The other ray vibrating in a plane perpendicular to \"e\angle of incidence (he is therefore known as the ordinary ray \"o\").

One can get a feeling for this when we take into account the tetrahedrons (see \"Glass Properties\").

If the tetrahedron structure is disturbed by strain then this will make it more or less difficult for a light beam to go through in that direction.

无应力玻璃是各相同性的，这表示光可以同样的方式通过玻璃，然而应力使玻璃成为各相异性。 将一束偏振光分解为两束彼此正交振动的偏振光，在简单的轴向拉应力或压应力的作用下一条光束始终在一个平面内振动，它包含轴向应力和随入射角变化的速率（此异常性能射线称为非常射线“e”）另一条射线在垂直于“e”的平面内振动，以一个同它的入射角无关的速率穿过玻璃（称为普通射线“o”）

How can we make use of these phenomena? Imagine the situation as shown in fig. 9.

我们怎么来利用这种现象呢？假象图9中展示的情况。

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Fig. 9. A light beam passing through the polarizer will vibrate only in one plane indicated by the vector R. These vector passing through the glass with strain will be resolved in two components, one parallel to the direction of the maximum strain (e) and the other one perpendicular to this direction (o).

As explained before e and o will travel with a different speed through the glass and therefore there will be a phase shift between the two components (also called \"retardation\").

矢量R表示一束光穿过偏振片后只在一个平面内振动，这些矢量通过应力玻璃后被分解为两个矢量，一个为平行于最大应力（e）方向，一个则垂直于这个方向（o）。

前面提到过，e和o以不同的速度穿过玻璃，因此两个分量之间将有一个相位差（也称为“滞后”）。

The formula is as follows： 公式如下：

D = C * Λ * d D = phase shift (nm) 相位差 Λ = strain (Pa) 应力

C = strain optical factor or Brewster-coefficient (nm/Pa.cm) 应力光或布鲁布斯系数） d = thickness of the glass (cm) 玻璃厚度

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If the phase shift equals 1/2 of the wavelength Σ (\"lambda\") or (1+1/2) Σ etc, then the new composed vector R1 coming out of the glass will be vibrating in the direction of the second polarizer (= analyser A). If the phase shift equals 1 x lambda (or a multiple ), then the new vector R1 will vibrate in the direction of the polarizer P but perpendicular to the analyser A which means extinct by A. So the result of the interference of the two \"component\" vectors will result in a R1 which will be in a plane in between (or up to) the P and A planes. This is a situation as explained in fig.5. The result is reinforcement or extinction and all possibilities in between.

如果相位差等于1/2波长λ或（1+1/2）λ波长，那么从玻璃中射出的新的矢量R1将在第二偏振片（＝偏振片A）的方向上振动，如果相位差等于λ（或λ的倍数），新矢量将在偏振片P的方向上振动，但垂直偏振片A，即将被A吸收，所以两个矢量分量干涉的结果是在R，A平面之间（或高于）的R1平面中，这就是在图5中解释过的情况，结果是增强或抵消都有可能。 The value of the phase shift is depending on the thickness of the glass (the longer the way the components have to travel the more phase shift), and the amount of strain in the glass (more strain means more phase shift).

相位差的大小取决于玻璃的厚度（分量穿过的距离越长相位差越大）和玻璃中应力的大小（应力越大，相位差越大）

With the set-up as shown we have now the possibility to \"see\" strain. (dark = no phase shift = no strain; light = phase shift = strain).

我们现在可以通过设定来“看到”应力了。（黑＝无相位差＝无应力；亮＝相位差＝应力） The practical problem is that in order to have sufficient phase shift a relatively big glass thickness is needed which isn't used in most of the products. Also it is very difficult to judge visually whether there is a lot of strain and what kind of strain based on the shade of grey which can be seen. In order to overcome these disadvantages and to increase the sensitivity of the measuring, the so called first order red plate has been introduced.

实际问题是为了获得足够的相位差就要使用在大多数产品中不使用的较厚的玻璃，同时用肉眼根据灰色的影子来判断有多少应力和应力的种类是非常困难的，为了克服这些不足并增强测量灵敏度，就要使用第一级辐射红光片。

What is the function of the red plate? 红光片的作用是什么？

The red plate is a medium which is so constructed that the phase shift between e and o of the polarized light coming through P equals a value somewhere in the green light .Different suppliers

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