2 uses of thinfilm interference?

Answer 1

To protect solar displays, and to protect telescopes and lenses.

It like create an optical filter, so the rays of the sun will not get directly to the lens or to the lens of the telescope.

Answer 2

An interference line filter is a useful application. It blocks all transmitted light except in an extremely narrow band, usually centered on an emission line of a laser or such. They are very useful for separating laser light from background light.

Answer 3

Create anti-reflective coatings, and create optical filters.