衍射和干涉的區(qū)別是一個(gè)困擾很多人的問題。由Eugene Hecht撰寫的教科書《Optics》給出了準(zhǔn)確、權(quán)威的回答。他說：
“There is no significant physical distinction between interference and diffraction. It has, however, become somewhat customary, if not always appropriate, to speak of interference when considering the superposition of only a few waves and diffraction when treating a large number of waves. Even so, one refers to multiple beam interference in one context and diffraction from a grating in another.”
就是說，干涉與衍射沒有顯著的物理區(qū)別。但是在某種程度的習(xí)慣上，即使這不總是恰當(dāng)?shù)模?dāng)只考慮幾個(gè)波的疊加時(shí)，我們稱之為干涉，當(dāng)處理大量波的疊加時(shí)，我們稱之為衍射。即便如此，人們說多個(gè)光束的干涉，但是說來自光柵的衍射。