Lecture 18 - ENGR 4250 Advanced Materials Engineering...

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ENGR 4250 – Advanced Materials Engineering Lecture 18 Optical Properties Ch 21; Callister 8/e Dr. A. Keshavarz - ENGR 4250U
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ISSUES TO ADDRESS. .. What happens when light shines on a material ? Why do materials have characteristic colors? Optical applications: -- luminescence -- photoconductivity -- solar cell -- optical communications fibers Why are some materials transparent and others not? Chapter 21: Optical Properties Dr. A. Keshavarz - ENGR 4250U
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Electromagnetic Radiation s m c / 10 3 1 8 0 0 × = = = µ λυ In vacuum Dr. A. Keshavarz - ENGR 4250U
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Electromagnetic Radiation Dr. A. Keshavarz - ENGR 4250U
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Dr. A. Keshavarz - ENGR 4250U
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Optical Properties Light has both particulate and wavelike properties – Photons - with mass λ = ν = hc h E m/s) 10 x (3.00 light of speed c ) s J 10 62 . 6 ( constant s Planck' frequency wavelength energy 8 34 = = = ν = λ = x h E Dr. A. Keshavarz - ENGR 4250U
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Phonon vs Photon Phonon Similarity Wave like Quantized Dissimilarity Elastic solids Velocity sound Photon Similarity Wave like Quantized Dissimilarity Electromagnetic Many media Velocity light Dr. A. Keshavarz - ENGR 4250U
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ATOMIC AND ELECTRONIC INTERACTIONS Dr. A. Keshavarz - ENGR 4250U
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Electronic Polarization 1 Radiation is absorbed 2 Light waves are retarded in velocity Dr. A. Keshavarz - ENGR 4250U
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Refractive Index, n Note: n = f ( λ ) Typical glasses ca. 1.5 -1.7 Plastics 1.3 -1.6 PbO (Litharge) 2.67 Diamond 2.41 medium) in light of (velocity vacuum) in light of (velocity v c Transmitted light distorts electron clouds. Light is slower in a material vs vacuum. n = refractive index + no transmitted light transmitted light + electron cloud distorts Selected values from Table 21.1, Callister 7e . --Adding large, heavy ions (e.g., lead can decrease the speed of light. --Light can be "bent" Dr. A. Keshavarz - ENGR 4250U
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Total Internal Reflectance φ φ = sin sin n n n ’(low) n (high) n > n 1 φ c φ ' 1 φ angle critical angle refracted angle incident = φ = φ = φ c i i reflected internally is light for 90 when occurs c i i c φ > ° = Dr. A. Keshavarz - ENGR 4250U
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Example: Diamond in air Fiber optic cables are clad in low n material for this reason. 5 . 24 41 . 2 1 sin sin 1 sin 90 sin 1 41 . 2 sin sin = φ = φ φ = φ = φ φ = c c c c n n Dr. A. Keshavarz - ENGR 4250U
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Incident light is either reflected, absorbed, or transmitted: S R A T o I I I I I + + + = Light Interaction with Solids Optical classification of materials: Adapted from Fig. 21.10, Callister 6e . (Fig. 21.10 is by J. Telford, with specimen preparation by P.A. Lessing.)
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Lecture 18 - ENGR 4250 Advanced Materials Engineering...

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