Lecture 39 - Interference for light

Lecture 39 - Interference for light - Like any other wave...

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1 Lecture 39 Interference Interference. Like any other wave Interference works like for any wave: at any given point, the E/B field is the vector sum of the E/B field from each wave. Constructive In phase (or out of phase by whole λ ) Destructive Out of phase by λ /2 Path difference L Constructive interference 12 0, 1, 2. .. Lrr m m      r 2 P At point P: S 2 Destructive interference 1 0, 1, 2. .. 2 Lrr m m    1 Two monochromatic coherent light sources S 1 Coherence S 1 and S 2 are two sources of monochromatic, coherent light. The phase difference between these two sources is constant. Easy trick to produce coherent light: split a beam in two. Light is produced by millions of atoms emitting at the same time, with random phases two light sources are in general incoherent
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2 Young s experiment Monochromatic light r 1 2 Max: Light and dark alternating fringes • Waves start off in phase at two slits • Travel different distances to screen • Relative phase at screen 12 0, 1, 2. .. Lrr m m     DEMO: Water wave interference Dark Dark Bright Bright Dark Dark Bright Bright Position of maxima/minima R
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Lecture 39 - Interference for light - Like any other wave...

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