Colors in nature are not only due to reflected wavelengths. Leaves – spectrum Butterfly – interference A thin film in on the butterfly’s wings creates the iridescent color. Bright Colors
Reflection from a fast medium causes no phase shift. High index of refraction to low index of refraction Reflection from a slow medium causes the phase to invert. Low index of refraction to high index of refraction Rebound Phase
At each boundary there are both transmitted and reflected waves. Like the string there can be a phase shift. Invert from a slow medium Boundary Effect
Extra Path • A thin film offers two separate boundaries for light. • Initial boundary from air to film – reflection with phase shift • Second boundary from film to air – reflection without shift
For a perpendicular ray a reflection from the second boundary has an extra path. Length 2d If this is equal to a whole number of wavelengths there will be destructive interference. First wave shifted Shorter wavelength in film Destructive Path
If the path equals to a half number of wavelengths there will be constructive interference. Second wave matches first Different wavelengths are enhanced by different thicknesses. Constructive Too
Soap Film • Soap film provides different thicknesses to cause different wavelength to undergo interference.
Newton’s Rings • Air or water between glass can also act as a thin film. • Different index of refraction next