Thin Film Interference for Soap Bubble ()1 2 2 Min (destructive) 2 Max (constructive) n n dm dm λ λ = =+ n n λ λ= Wavelength inside soap! Interference due to thin film reflection (e.g. B. Thin-Film Interference . Example: Thin film of air: Glass Air Glass L For a given (vacuum) wavelength of normally incident light, which equation gives the film thicknesses for constructive interference of reflected light? 2L m m , m 0, 1, 2, . m A. • A net phase shift difference of p due to reflection • Beam 2 has a phase shift due to path difference Phase shift p Introduction to Thin Film Technology Introduction to Thin Film Technology Verfahrenstechnik der Oberflächenmodifikationen Prof. Dr. Xin Jiang Lecture Institut für Werkstofftechnik der UniInstitut für Werkstofftechnik der Uni- -SiegenSiegen Sommersemester 2007 Prof. Dr. X. Jiang, 23.06.2008. Thin film interference can also be modeled with the light is not normal to the thin film surface, the only added complexity is a sine or cosine term in the mathematical model which doesn't add any further insight into the physics behind the interference, thus we constrain ourselves to the simpler algebraic model when light is normal to the thin film surface. Examples of Thin-Film Interference Soap bubble Thin oil film. So, what are the rules for how waves reflect from surfaces - what happens to the phase? Sunlight that reflects off a thin film of oil floating on a puddle of water will exhibit thin film interference in an interesting manner that comes about because the light is comprised of many wavelengths, and the film of oil is not uniform in thickness. Let r 1 be the length of the path taken by the light from one source to the observation point and let r 2 be the length of the path taken by the light from the other source to the observation point, so that jr 2 r 1jis the path di erence. film in air) Beams 1 and 2 reflected off the front and back surfaces of a thin film combine to show interference effects. 2 L (m 1 2) , m 1 , 2 , . Thin Film Interference When light hits a surface, it can be absorbed, transmitted or reflected. n d Similar analysis, but… ¾Phase shift of ½ λfor air–soap reflection ¾No phase shift for soap–air reflection ¾Net ½ λphase shift switches max ↔min. C. Neither of the above equations. Thin-Film Interference INTRODUCTION Interference occurs when the light of wavelength, , from two coherent sources arrives at the same point. LOT Chair of Surface and Materials Technology Introduction to Thin Film Technology FACHBEREICH MASCHI