光的干涉optics03.film interference

1、Amplitude-splitting Interferometers,7.4.1 Dielectric Films-Double-Beam Interference (Thin-Film Interference) 7.4.2 Mirrored Interferometers,Contents,Thin-film interference 1.Fringes of equal inclination 2.Fringes of equal thickness: wedge thin-film and Newtons rings. Mirrored interferometers 1.Miche

2、lson interferometer 2.Mach-Zehnder interferometer 3.Sagnac interferometer.,Teaching purpose:,知道各干涉仪的装置，会画出示意图； 会计算两束反射光（或折射光）之间的光程差，并讨论干涉花纹； 会利用干涉仪进行微小测量，波长测量等。,New words,1.The index of refraction and the speed of light The index of refraction of a medium is the ratio of the speed of light in vacuum

3、 to its speed in the transparent medium. The frequency of the light is the same in both medium.,then,Fringes of equal inclination,2.Equivalent path difference and phase difference Equivalent path= geometrical path index of refraction,Fringes of equal inclination,Optical path 光程= n r Optical path dif

4、ference 光程差 =n2r2-n1r1 Phase difference =2/0,n1,n2,S2,S1,r2,r1,p,Fringes of equal inclination,3.thin-film interference-amplitude division,Medium n1, n3 Thin-film n2, d Incident light, ,i,r Reflect light 2 and 3 is coherent. Transmission light 4 and 5 is coherent.,Fringes of equal inclination,Optical

5、 path difference of reflect light 2,3 Phase difference,Phase changes upon reflection must be done on a case by-case basis,Fringes of equal inclination,Optical path difference of transmission light 4,5 Phase difference,Fringes of equal inclination,phase changes upon reflection if i=0, Phase differenc

6、e= Phase difference,Reflection light has phase change,Transmission light has phase change,Fringes of equal inclination,Fringes of equal thickness,In our daily life the color fringes on an oil film or on a soap bubble are often seen. These are common examples of interference taking place in thin film

7、.,1.wedge thin-film Optical path difference,Fringes of equal thickness,The interference fringes trace out contours of constant thickness of the wedge thin-film. The thickness difference between adjacent bright (dark)fringes The fringes width(space between adjacent dark fringes),Fringes of equal thic

8、kness,Example 1: A broad beam of red light, with wavelength =632.8 nm, incidences on am air wedge as shown in figure. An observer looking dowm on the block with the air wedge sees an interference pattern consisting of six dark fringes and five bright red fringes along the wedge. What is the change i

9、n thickness T(=TR-TL) along the wedge?,Fringes of equal thickness,Solution: At the left and right ends ,dark fringe implies the destructive interference,Fringes of equal thickness,5.Newtons rings Optical path difference: Phase difference Newtons rings traced out contours of constant thickness of the

10、 air gap between the surfaces.,Fringes of equal thickness,Therefore The radius of the Newtons rings:,Fringes of equal thickness,Fringes of equal thickness,Example 2: A glass lens is coated on one side with a thin film of magnetium fluoride (MgF2) to reduce reflection from the lens surface. The index of refraction of MgF2 is 1.38; that of the glass is 1.50. What is the least costing thickness that eliminates the reflections at the middle of the visible spectrum (=550nm)? Assume that the light is approximately perpendicular to the l