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Published byLorenzo Branham Modified over 9 years ago
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1 monochromatic! Interference Colors What changes for other colors (wavelengths)?What changes for other colors (wavelengths)? Δ = d (n s - n f ) Δ = d (n s - n f ) 1 1.5 Δ= /2 d fast slow
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2 Interference Colors Story above was for one wavelength (color) of lightStory above was for one wavelength (color) of light Retardation distance (Δ) is ~same for all colors, but:Retardation distance (Δ) is ~same for all colors, but: – Δ = m -> no ray (rotation = 0° or 180°) – Δ = [(m-0.5) ] -> max.ray (rot.=90°, 270°) Certain wavelengths get blocked at analyzer, others passCertain wavelengths get blocked at analyzer, others pass –produces an “interference color” –show Excel calculation
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3 Thickness effect Δ = d (n s - n f ) Δ = d (n s - n f ) quartz wedge demoquartz wedge demo – = (n s - n f ) = 0.009 (a small value) –shows change in set of transmitted wavelengths (i.e., color) with increasing retardation, Δ
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4 Birefringence effect Δ = d (n s - n f ) = d Δ = d (n s - n f ) = d –can get same set of colors by varying at constant d maximum is characteristic of mineral!maximum is characteristic of mineral! –e.g., calcite = 0.172 (a large value) –quartz = 0.009 (a small value) orientation-dependentorientation-dependent – (=n s -n f ) ranges from 0 to a maximum –0 is looking along “optic axis”
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5 Interference Color Chart thickness, d (µm) retardation, Δ (nm) birefringence, quartz? range of colors - same as quartz wedgerange of colors - same as quartz wedge measuring birefringencemeasuring birefringence
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6 Interference Color Chart thickness, d (µm) retardation, Δ (nm) birefringence, OrdersOrders Every 550 nm (≈ blue )Every 550 nm (≈ blue )
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7 Interference Color Chart Two kinds of whiteTwo kinds of white –low-order –high-order = 0.172 d = 30 µm what color is out here?
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