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PRACTICE / Thin-film interference

Use the internal angle for the film phase

A nondispersive index-1.50 film in air has a fixed-order reflected maximum at 600 nm at normal incidence. For s-polarized light the external incidence angle is changed so that sin i = 0.90; the relative reflection phase remains unchanged.

At what vacuum wavelength does the same order now peak?

Organize the givens & assumptions
  • nf = 1.50
  • sin i = 0.90
  • Normal-incidence maximum = 600 nm

Coherent s-polarized light, nondispersive transparent film, fixed interference order, unchanged reflection-phase difference. Use the common-wavefront path difference and Snell’s law.

  1. A480 nm480\ \mathrm{nm}
  2. B360 nm360\ \mathrm{nm}
  3. C750 nm750\ \mathrm{nm}
  4. D540 nm540\ \mathrm{nm}

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