11-3工程光学课件

1、第三节 干涉条纹的可见度 The visibility (contrast) of interference fringesK表征了干涉场中某处干涉条纹亮暗反差的程度。可见度(Visibility, Contrast)定义：1式（11-14）光强与可见度的关系：2一、振幅比 对条纹可见度的影响3二、光源宽度 的影响和空间相干性相干性（Coherence）相干性与干涉（Coherence & interference）xI点光源产生的干涉条纹xI扩展光源产生的干涉条纹41、光源宽度 对条纹可见度的影响Pr1r2OS1S2SS0 x1r2rSdxcdblDl1l2x56讨论：1）光源的临界宽度：条

2、纹可见度为0时的光源宽度2）光源的允许宽度：能够清晰地观察到干涉条纹时，允许的光源宽度72、空间相干性（Spatial Coherence )若通过光波场横向两点的光在空间相遇时能够发生干涉，则称通过空间两点的光具有空间相干性。k81S20 xebclDxS120d9三、光源非单色性 的影响和时间相干性1、光源非单色性 对条纹可见度的影响10讨论：相干长度(coherence length)：对于光谱宽度为（或k）的光源能够产生干涉的最大光程差。112、时间相干性 (Temporal Coherence)时间相干性：若同一光源在相干时间内发出的光经过不同的路径在空间相遇时，能够产生干涉，则称光

3、具有时间相干性。(光程差存在条件下产生干涉)相干时间 t：光通过相干长度所需的时间。（光波谱宽）公式：12Partial Coherence & contrastIt is incorrect to think of light as either coherent or incoherent. Light can have different degrees of coherence,which introduced the concept of partial coherence.Complete coherence is merely a theoretical limit. 13Par

4、tial Coherence & contrastAssume that two wavetrains of light, each of finite length s, overlap to their full extent. Such complete overlap will result in distinct maxima and minima of the highest degree of contrast. But even if the wavetrains overlap only in part, interference is possible. Although

5、the degree of contrast of the fringes is less, depending on the degree of overlap.14本课内容回顾2、振幅比与可见度的关系：3、光源宽度与可见度的关系4、光源单色性与可见度的关系5、名词解释：空间相干性、时间相干性、相干长度、相干时间、干涉孔径角1、可见度的定义15Homework1. 比较说明空间相干性和时间相干性的联系和区别。P2446&7下一节16VisibilityIt can be defined as K=(Imax-Imin)/(Imax+Imin) where Imax and Imin are

6、the intensities at the maxima and minima of the fringe pattern.返回17ContrastIt can be defined as the ratio of the difference between maximum areance Emax, and mimimum areance, Emin, to the sum of such areances:K=(Emax-Emin)/(Emax+Emin) The amount of power incident per unit area is called areance (ill

7、uminance).返回18CoherenceThe property of light necessary to produce interference is called coherence.返回19Coherence & InterferenceCoherence is a property of light. Interference is the process of interaction. Coherence means that two or more waves in a radiation field are in a fixed and predictable phas

8、e relationship to each other.We distinguish two classes of coherence, spatial coherence and temporal coherence.返回20Spatial CoherenceSpatial coherence or, more precisely transverse spatial coherence refers to the phase relationship between waves traveling side by side, at a certain distance from one another. The farther apart the two waves, and the less coherent the light will be.返回21Coherence LengthThe length of a wavetrain, s, is called coherence length.返回22Temporal CoherenceTemporal coherence or, longitudinal spatial coherence (often called mono