Interference in thin films(薄膜干涉) Two things must be noted: 1.The phase shift due to reflection. 2.The wavelength of light An in a medium whose refraction index is n is n Where A is the wavelength of the light in free spaceInterference in thin films（薄膜干涉）: Two things must be noted: 1. The phase shift due to reflection. 2. The wavelength of light n in a medium whose refraction index is n is Where  is the wavelength of the light in free space