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Unformatted text preview: 1 Lecture 40 Thin films Interferometers Thin films. Interferometers. Thin films: experimental results air These two reflections produce a double slit interference Ray 2 travels a slightly longer distance than ray 1 1 2 t n pattern but the dark and bright spots are interchanged! Theres an extra phase shift of or /2 somewhere film air Phase change upon reflection From waves in 221: Reflection of a wave on a fixed/free boundary Fixed Free Phase shift = Phase shift = 0 A similar thing applied to EM waves (can be fully proved using Maxwells equations) Reflection upon slower medium Fixed boundary Phase shift = Reflection upon faster medium Free boundary Phase shift = 0 2 Thin films: qualitative analysis air 1 2 Phase shift = Overall phase difference: 2 n k t t n n From wave 1 From wave 2, for normal incidence (figure shows angles for clarity) 2 2 t n air 2 2 n n n k...
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