Wedge Thin Film
Wedged thin films have a linearly varying thickness across the surface, creating spatially varying interference. Used in optical testing (Newton's rings, Fizeau interferometry), linear-variable filters, and precision thickness measurement. The fringe spacing Δx = λ / (2n·tan α) determines the spatial period of constructive interference.
Fringe spacing Δx = 0.067 mm
Thickness at x = 0 = 58.5 nm
Δx = λ / (2·nf·tan α) — spacing between adjacent bright fringes
Model and references
Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers
Thin-wedge approximation at normal incidence: each point is a plane-parallel film of the local thickness, with exact matrix R. Small angles only; beam tilt, fringe localization and coherence length are ignored.
- Hecht E. (2016). Optics, 5th ed., §9.4 (fringes of equal thickness).
- Born M., Wolf E. (1999). Principles of Optics, 7th ed., §7.5. Cambridge University Press.
- Macleod H. A. (2010). Thin-Film Optical Filters, 4th ed., ch. 2. CRC Press. doi:10.1201/9781420073034