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Lect18 - Wave Optics First lecture on Chapter 25 Physics...

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11/7/11 1 Wave Optics Coherence and condi,ons for interference Michelson Interferometer Thin Flms Single slit Double slit 11/7/11 Physics 104, Fall 2011 Physics 104 Lecture 18 Nov. 7, 2011 First lecture on Chapter 25 Light: wave or particle? The field of wave optics studies the properties of light that depend on its wave nature Originally (Newton) light was thought to be a particle and that model successfully explained the phenomena discussed in geometric options Other experiments revealed properties of light that could only be explained with a wave theory Maxwell’s theory of electromagnetism convinced physicists that light was a wave When dealing with sizes comparable to or smaller than the wavelength± wave op,cs is required Examples include interference e²ects and propaga,on through small openings Even more experiments led to the quantum theory of light Light has proper,es of both waves and par,cles November 11 Physics 104, Fall 2011 2

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11/7/11 2 Interference One property unique to waves is interference Interference of sound waves can be produced by two speakers When the waves are in phase , their maxima occur at the same time at a given point in space Question November 11 Physics 104, Fall 2011 4 + Different frequency 1) Constructive 2) Destructive 3) Neither -1.5 -1 -0.5 0 0.5 1 1.5 -1.5 -1 -0.5 0 0.5 1 1.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5
11/7/11 3 Interference Requirements Two (or more) waves Same Frequency Coherent (waves must have defnite phase rela,on) Strategy ±or inter±erence experiments: “split” a light wave and superimpose the split waves with each other (path di²erence o± split waves must be small³ so that coherence condi,on is s,ll ±ulflled) November 11 Physics 104, Fall 2011 5 Interference with Light No coherence o± light ±rom two separate sources. f ≈ 10 14 Hz November 11 Physics 104, Fall 2011 6 Single source Two different paths Interference possible here • Split one wave from single source into two or more and have them take different paths Two slits Reflection (thin films) Diffraction

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11/7/11 4 Michelson Interferometer The Michelson interferometer is based on the interference of reflected waves Two reflecting mirrors are mounted at right angles A third mirror is partially reflecting Called a beam splitter The incident light hits the beam splitter and is divided into two waves The waves reflect from the mirrors at the top and right and recombine at the beam splitter The only difference between the two (split and identical) waves is that they travel different distances between their respective mirrors and the beam splitter The path length difference is Δ L = 2L 2 – 2L 1 Link to a nice anima,on Michelson
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Lect18 - Wave Optics First lecture on Chapter 25 Physics...

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