What is the thinnest film that will highly reflect near-ultraviolet light of wavelength 350 nm?

KrisTina Marie: What is the thinnest film that will highly reflect near-ultraviolet light of wavelength 350 nm?
A thin film with index of refraction n-film = 1.38 is used to coat a lens, which has n-lens = 1.50. What is the thinnest film that will highly reflect near-ultraviolet light of wavelength 350 nm? What is the thinnest film that will minimize reflection of 700 nm light?

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Answer by Nathan
AuAg will help as well as aluminite. Light is a frequency wave, you will not get a perfect answer until you better understand Gauss