洲第十二章光的衍射( Diffraction) 光的衍射现象:光波在空间传播遇到障碍时,其传 播方向会偏离直线传播,弯入到障 碍物的几何阴影中,并呈现光强的 不均匀分布的现象。 天津大学精仪学院 天津大学作 24
1 第十二章 光的衍射（Diffraction） 光的衍射现象：光波在空间传播遇到障碍时，其传 播方向会偏离直线传播，弯入到障 碍物的几何阴影中，并呈现光强的 不均匀分布的现象
What is the diffraction When light passes through a narrow slit it spreads out more than what could be 天津大学精仪学院 accounted for by geometric construction This is an example of diffraction Diffraction can be defined as any departure from the predictions of geometric optics 天津大学作 24
2 When light passes through a narrow slit, it spreads out more than what could be accounted for by geometric construction. This is an example of diffraction. Diffraction can be defined as any departure from the predictions of geometric optics. What is the Diffraction?
Diffraction e The phenomenon that the light waves tend to bend around and become spread out when they pass near a barrier is called 天津大学精仪学院 diffraction Diffraction of light occurs when a light wave passes by a corner or through an opening or slit that is physically the approximate size of, or even smaller than that light's wavelengtH 天津大学作 24
3 • The phenomenon that the light waves tend to bend around and become spread out when they pass near a barrier is called diffraction. • Diffraction of light occurs when a light wave passes by a corner or through an opening or slit that is physically the approximate size of, or even smaller than that light's wavelength. Diffraction
过 Related Concept The terms difraction and scattering are often used interchangeably and are considered to be almost synonymous 天津大学精仪学院 Diffraction describes a specialized case of light scattering in which an object with regularly repeating features(such as a diffraction grating produces an orderly diffraction of 天害大学顺华 ight in a diffraction pattern 24
4 Related Concept • The terms diffraction and scattering are often used interchangeably and are considered to be almost synonymous. • Diffraction describes a specialized case of light scattering in which an object with regularly repeating features (such as a diffraction grating) produces an orderly diffraction of light in a diffraction pattern
In the real world most objects are very complex in shape and should be considered to be 天津大学精仪学院 composed of many individual diffraction features that can collectively produce a random scattering of light 天速大学作 24
5 • In the real world most objects are very complex in shape and should be considered to be composed of many individual diffraction features that can collectively produce a random scattering of light
衍的实验 Diffraction experiment: Barrier Se creen K 天津大学精仪学院 ight source 光的是光的波动性的主要标志之 天津大学作 24
6 衍射实验(Diffraction experiment)： S K 光的衍射是光的波动性的主要标志之一。 Light source Barrier Screen
舵别现象的分类 ( Classification of light difraction): 根据光源、衍射物(衍射屏)和衍射场(观察屏)三 者之间的位置确定 1)夫琅和费衍射( raunhofer diffraction): 天津大学精仪学院 光源和衍射场都在衍射物无限远处的衍射 2)菲涅耳衍射( Fresnel diffraction) 光源和衍射场或二者之一到衍射物的距离比较 小时的衍射。 天津大学作 24
7 衍射现象的分类 (Classification of light diffraction)： 根据光源、衍射物（衍射屏）和衍射场（观察屏）三 者之间的位置确定 （1）夫琅和费衍射(Fraunhofer diffraction)： 光源和衍射场都在衍射物无限远处的衍射。 （2）菲涅耳衍射（ Fresnel diffraction ）： 光源和衍射场或二者之一到衍射物的距离比较 小时的衍射
第一节光波的标量衍射理论 惠更斯一菲涅耳原理 1、惠更斯原理( urges' principle): (1)波阵面的形成, 天津大学精仪学院 (2)波面的传播方向。 D 天津大学作 图12-3光波通过圆孔的惠更斯作图法 24
8 第一节 光波的标量衍射理论 一、惠更斯－菲涅耳原理 1、惠更斯原理 (Huygens’ principle)： （1）波阵面的形成， （2）波面的传播方向。 图12－3 光波通过圆孔的惠更斯作图法 S D D' K v
2、惠更斯一菲涅耳原理 波阵面外任一点光振动应该是波面上所有 子波相干叠加的结果 天津大学精仪学院 图1点光源和P点的作用 天津大学作 9 24
9 S Z P r R Q Z' 图1 点光源S对P点的作用 2、惠更斯－菲涅耳原理 波阵面外任一点光振动应该是波面上所有 子波相干叠加的结果
波阵面外任一点光振动应该是波面 光源在波面Z上上所有子波叠加的结果 任意Q点产生的复振幅: E=A exp(ikR) R Q点处do大小的面元 天津大学精仪学院 对P点的贡献为: dE(P)=Ck(0).Eo exp(ikr) O 子波向P点的球面波公式 子波法线方向的振幅 天津大学作 子波振幅随θ角的变化 10 24
10 波阵面外任一点光振动应该是波面 上所有子波相干叠加的结果。 S Z P r R Q Z' ( ) ( ) ( ) d r ikr dE P CK EQ ~ ~ exp = 子波向P点的球面波公式 子波法线方向的振幅 子波振幅随角的变化 ( ) R ikR E A Q S ZZ Q ~ exp ' = 任意 点产生的复振幅： 光源 在波面 上 Q d P 点处 大小的面元 对 点的贡献为：