同济大学：《大学物理》课程教学资源（电子教案，英文版）第二十章 光学（下）

The diffraction of light waves

The diffraction of light waves

Agenda today 1.Single slit diffraction 2.Diffraction by a circular aperture 3.Optical grating 4.X-ray diffraction32

Agenda today 1. Single slit diffraction 2. Diffraction by a circular aperture 3. Optical grating 4. X-ray diffraction32

Diffraction Fresnel diffraction:ifa source s and the viewing screen are each a finite distance from an intermediate object,the resulting diffraction pattern is called fresnel diffraction(菲涅尔衍射）

Diffraction Fresnel diffraction：if a source s and the viewing screen are each a finite distance from an intermediate object, the resulting diffraction pattern is called fresnel diffraction(菲涅尔衍射）。 P

Fraunhofer diffraction:if both the source and the screen are far from the intermediate object,the diffraction is called fraunhofer diffraction(夫朗和 费衍射)。 D

Fraunhofer diffraction：if both the source and the screen are far from the intermediate object, the diffraction is called fraunhofer diffraction(夫朗和 费衍射）。 P

Single slit diffraction(单缝衍射) 夫琅禾费单缝衍射 2 S 0 B

Single slit diffraction(单缝衍射）

For constructive asin0=±(2k+1) interference For destructive asin0=±kλ minima interference 2 0 -2

For constructive interference ： sin (2 1) 2 a k      a k sin    minima01-2-12 For destructive interference

asi o A 0 D 入/2 a 几 asin=n 2

oP   BA asin  a sin 2 a n    /2

2 0 -2 asin0=±k入 the angular width of<asin< central maxima: Φ=20≈2sin0= 22 a

0 1 -2 -1 2  the angular width of central maxima： a k sin          asin 2 2 2sin a       

Diffraction pattern with different slit width: 0.16mm 0.08mm 0.04mm 0.02mm

Diffraction pattern with different slit width: 0.16 mm 0.08 mm 0.04 mm 0.02 mm

Intensity in single-slit diffraction For point o0=0,△p=0 △E Eo Eo For point P:Ep<Eo Ep △E

Intensity in single-slit diffraction For point o  = 0 ,  = 0 E0 E0 …… E0 = N E0 For point P： EP < E0  EP E0