Chem 24 Microscopy Lectures

Chem 24 Microscopy Lectures - Optics and Ultra-High...

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Optics and Ultra-High Resolution Microscopies Ray Approximation Wave Approximation Speed of light through a medium Diffraction Limit Standard microscopes Confocal Microscopy Ultra-High Resolution Optical Imaging Techniques
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Ray Approximation wave fronts rays are straight lines perpendicular to the wave fronts If a wave meets a barrier (assume that << d, where d is the width of the opening) then the light passes right through
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Ray Approximation specular reflection is reflection from a smooth surface Law of Reflection 1 ' = 1 the incident ray the reflected ray and the normal are all in the same plane
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Ray Approximation light enters from left light may encounter an electron electron may absorbe the light it may oscillate, and then reradiate the light The absorption and radiation cause the average speed of the light moving through the material to decrease Thus, the speed of light in some material is less that its speed in a vacuum n = refractive index = speed of light in vacuum = c speed of light in a medium v for a vacuum n =1 for other media n <1 for air, n =1.00029
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Ray Approximation Frequency between media As light travels from one medium to another, its frequency does not change but the speed, and thus the wavelength, do change n = f on both sides of the interface separating the two media 2 2 1 1 n n 2 2 1 1 cos cos n n Snells Law of refraction
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Huygen's Principle Huygens assumed light is a form of wave motion rather than a stream of particles His principle is a geometric construction for determining the position of a new wave at some point based upon the knowledge of that wave front that proceeded it
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The law of refraction Ray 1 strikes the surface and at a time interval t later, ray 2 strikes the surface During this time interval, the wave at A sends out a wavelet, centered at A, towards D 2 1 2 1 sin sin v v 1 2 2 1 2 1 sin sin n n n c n c 2 2 1 1 sin sin n n so Snell's Law
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Wave Approximation The index of refraction for a material enerally decreases with increasing wavelength Violet light bends more tha red light when passing through a refracting material This wavelength dependence explains how prisms spread white light out into its spectrum a raindrop high in the sky refracts so that the observer on the ground sees red. A low altitude raindrop refracts violet light to the observer on the ground And it explains rainbows
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Wave Approximation n 2 <n 1 normal There is a particular angle of incidence that will result in an angle of refraction of 90 o with respect to the normal This is called the critical angle c 2 1 2 1 sin n n n n for c basis of fiber optics light transmission
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The resolution of a microscope (or telescope) can be thought of as a diffraction, or, more properly, interference, limit. light beam
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Chem 24 Microscopy Lectures - Optics and Ultra-High...

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