大学物理英文[].pptVIP

Lesson 10 * Chapter 13 Diffraction(4 hours) 13-1 The Diffraction of Light 13-2 Single-Slit Diffraction 13-3 Diffraction by a Circular Aperture 13-4 The Diffraction Grating 13-5 X-Ray Diffraction 13-6 Holography 13-1 The Diffraction of Light A single slit An opaque disk A circular aperture Diffraction of light occurs when a portion of the wavefront is limited by an obstacle. Diffraction pattern of: S L1 L2 A E Two types of diffraction Fraunhofer diffraction and Fresnel diffraction. Fraunhofer diffraction occurs when the source and the screen are far from the obstacle and the light is essentially parallel; it is a matter of far-field diffraction . Fresnel diffraction occurs when the source or screen, or both of them, are finite distance from the obstacle; it is a matter of near-field diffraction. S A E 13-2 Single-Slit Diffraction P E O a ? f A B 1. Experimental arrangement to the focal plane of the lens. When the diffracted light reaches viewing screen E, waves from different points within the slit undergo interference and produce a diffraction pattern of bright and dark fringes (interference maxima and minima) on the screen. The lens ensures that rays which reach any point on screen E are exactly parallel back at the slit and directed 1 2 3 4 5 6 7 8 9 A B y I Focal plane P 2.Explanation BC = a sin? D a C P0 P1 P2 P3 P4 BC = a sin? C B A 3.Locating bright and dark fringes A B BC=a Sin? C a Dark fringes Bright fringes 0 Central bright fringe 3.Locating bright and dark fringes a A B C BC=asin? y I Checkpoint 1 4. Intensity distribution in single-slit diffraction sin? I 0 Dark fringes Bright fringes 0 Central bright fringe 1. Angular width of fringes sin? I 0 f(D) a). Central bright fringe Half angular width Linear width Discussion Angular width b).Other bright fringes Half angular width of central bright fringe 2. Fringe spacing Diffraction is distinct. Diffraction is n