(a) A thin film of oil ( ) floats on water ( ), with air ( ) above. For light of…

PHYSICS · Subjective · Fermi University Physics · Optics & Photonics · Interference and diffraction · Interference and diffraction

Optics and Photonics, Ch Multiple-beam interference: thin films, multilayers and the Fabry-Perot etalon

Problem

(a) A thin film of oil (nf=1.45n_f = 1.45) floats on water (nw=1.33n_w = 1.33), with air (n0=1.00n_0 = 1.00) above. For light of wavelength 550550 nm normally incident from air, find the thinnest film that gives a bright reflection, counting the reflection phase changes at each interface. (b) A single-layer antireflection coating of magnesium fluoride (nf=1.38n_f = 1.38) is to be deposited on a glass substrate of index ns=1.60n_s = 1.60, for light of wavelength 520520 nm. State the ideal (index-matching) refractive index for a coating on this glass, and find the thickness of the actual magnesium fluoride layer used. (c) An air-spaced (n=1.00n=1.00) Fabry-Perot etalon has mirror spacing d=3.00d = 3.00 mm and mirror reflectance R=0.85\mathcal{R} = 0.85. Find its free spectral range (in GHz) and its finesse.

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