Optics
Thin Film Interference
Condition for constructive interference in thin films (when one reflection has phase shift). For destructive: 2nt = mλ.
Variables
nunitless
Refractive index of film
Allowed values: 1 or more
tm
Film thickness
Allowed values: greater than 0
munitless
Order number
Allowed values: 0 or more, whole number
λm
Wavelength in vacuum
Allowed values: greater than 0
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- n = 1.5 (Refractive index of film)
- m = 3 (Order number)
- λ = 4 m (Wavelength in vacuum)
Result: t = 4.6666667 m
Other optics formulas with the same quantities
- Diffraction Grating (Wave Optics) shares Order number
- Resolving Power of Grating (Wave Optics) shares Order number
Where this formula is listed
- Optics formulas, under Wave Optics, alongside Fringe Spacing, Single-Slit Diffraction, Optical Path Length and Constructive Interference Condition.
- In the optics list it comes after Resolving Power of Grating and before Optical Path Length.
- Optics formula sheet, one of 34 formulas printed with symbol keys and SI units.
- The full formula index, grouped by category and topic.
Common questions
What is the Thin Film Interference formula?
Thin Film Interference is written 2nt = (m + 1/2)λ. Condition for constructive interference in thin films (when one reflection has phase shift). For destructive: 2nt = mλ. It belongs to Optics, under Wave Optics.
What are the units in 2nt = (m + 1/2)λ?
In SI units, n is refractive index of film (dimensionless); t is film thickness, measured in m; m is order number (dimensionless); λ is wavelength in vacuum, measured in m.