Fresnel_Diffraction_Themed_PPT.pptx wmiwoabj

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1. Fresnel Diffraction An overview of near-field diffraction phenomena. Image Placeholder

2. Introduction Diffraction is the bending/spreading of light when it encounters edges or small openings. Fresnel diffraction occurs when source and screen are at finite distances. Image Placeholder

3. Conditions - Source distance finite - Screen distance finite - Aperture size comparable to wavelength - Called near-field diffraction. Image Placeholder

4. Principle Based on Huygens–Fresnel principle: each point of a wavefront acts as a secondary source. Fresnel introduced half-period zones for analysis. Image Placeholder

5. Fresnel Zones Wavefront divided into concentric half-period zones. Each successive zone contributes with phase difference of 180°. Net intensity is partial cancellation and reinforcement. Image Placeholder

6. Mathematical Idea Radius of nth Fresnel zone: rₙ = √(n λ z) λ = wavelength, z = distance to screen, n = zone number. Image Placeholder

7. Types of Fresnel Diffraction 1. At a straight edge: bands near edge 2. Through a slit: central band + fringes 3. By a circular aperture: Arago’s spot Image Placeholder

8. Applications • Zone plates • Optical instruments • Microscopy • Diffraction testing of materials Image Placeholder

9. Comparison with Fraunhofer Diffraction Fresnel: finite distances, spherical wavefront, unequal fringes. Fraunhofer: infinity/lenses, plane wavefront, equally spaced fringes. Image Placeholder

10. Conclusion Fresnel diffraction proves the wave nature of light and explains near-field diffraction patterns observed in everyday optics. Image Placeholder