Newton's rings are a classic textbook manifestation of thin-film interference, observable when a spherical surface is placed in contact with a flat glass plate, and require no special citation.
The claim states that Newton's rings are caused by thin-film interference, which is a foundational and universally taught physical phenomenon of optics (common knowledge). None of the retrieved papers specifically address Newton's rings, as they cover modern topics like laser microfabrication, thermal concealment, and Fourier ptychography. Therefore, no citation is needed.