11-3工程光學(xué)課件

1、第三節(jié) 干涉條紋的可見(jiàn)度 The visibility (contrast) of interference fringesK表征了干涉場(chǎng)中某處干涉條紋亮暗反差的程度?？梢?jiàn)度(Visibility, Contrast)定義：1式（11-14）光強(qiáng)與可見(jiàn)度的關(guān)系：2一、振幅比 對(duì)條紋可見(jiàn)度的影響3二、光源寬度 的影響和空間相干性相干性（Coherence）相干性與干涉（Coherence & interference）xI點(diǎn)光源產(chǎn)生的干涉條紋xI擴(kuò)展光源產(chǎn)生的干涉條紋41、光源寬度 對(duì)條紋可見(jiàn)度的影響Pr1r2OS1S2SS0 x1r2rSdxcdblDl1l2x56討論：1）光源的臨界寬度：條

2、紋可見(jiàn)度為0時(shí)的光源寬度2）光源的允許寬度：能夠清晰地觀察到干涉條紋時(shí)，允許的光源寬度72、空間相干性（Spatial Coherence )若通過(guò)光波場(chǎng)橫向兩點(diǎn)的光在空間相遇時(shí)能夠發(fā)生干涉，則稱(chēng)通過(guò)空間兩點(diǎn)的光具有空間相干性。k81S20 xebclDxS120d9三、光源非單色性 的影響和時(shí)間相干性1、光源非單色性 對(duì)條紋可見(jiàn)度的影響10討論：相干長(zhǎng)度(coherence length)：對(duì)于光譜寬度為（或k）的光源能夠產(chǎn)生干涉的最大光程差。112、時(shí)間相干性 (Temporal Coherence)時(shí)間相干性：若同一光源在相干時(shí)間內(nèi)發(fā)出的光經(jīng)過(guò)不同的路徑在空間相遇時(shí)，能夠產(chǎn)生干涉，則稱(chēng)光

3、具有時(shí)間相干性。(光程差存在條件下產(chǎn)生干涉)相干時(shí)間 t：光通過(guò)相干長(zhǎng)度所需的時(shí)間。（光波譜寬）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本課內(nèi)容回顧2、振幅比與可見(jiàn)度的關(guān)系：3、光源寬度與可見(jiàn)度的關(guān)系4、光源單色性與可見(jiàn)度的關(guān)系5、名詞解釋?zhuān)嚎臻g相干性、時(shí)間相干性、相干長(zhǎng)度、相干時(shí)間、干涉孔徑角1、可見(jiàn)度的定義15Homework1. 比較說(shuō)明空間相干性和時(shí)間相干性的聯(lián)系和區(qū)別。P2446&7下一節(jié)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