教程說(shuō)明案例21-3interference from thin films

1、The colors are caused by the interference of light waves reflected from front and back surfaces of a thin transparent film. Interference from thin filmsPLDC34E5A1B2一Interference caused by reflection Traveling light path differenceReflection phase shift When a wave traveling in a lighter medium reach

2、es the interface with the denser medium, the transmitted wave has the same orientation as the incident wave, but the reflected wave is inverted. When a wave traveling in a denser medium reaches the interface with the lighter medium, the wave is partially transmitted and partially reflected, with no

3、change in orientation.1n2np1n光疏到光密the phase changep特別對(duì)正入射或掠入射情況airoil slickglass2n3n1nppsample 1:glass3n1nsample 2:airglass2npThe condition of reflection is sameaccessional phase differencerjpp0accessional light path differenced2l2l0dAccessional light path difference caused by reflectiond2l2l0rjp0p反

4、射條件The condition of reflection is differentaccessional phase differenceaccessional light path differenceminimaPLDC34E5A1B2maximaThe total light path difference during the reflection when the incident angle is zero if if 二 Interference of transmitting lightPPLDE5A1B2C34F Traveling path differenceairo

5、ilglass2n3n1nsample 1:pglass3n1nsample 2airglass2nppAccessional path difference caused by the reflection of transmitting light The condition of reflection is sameaccessional phase differencerjpp0accessional light path differenced2l2l0d2l2l0rjp0p反射條件The condition of reflection is differentaccessional

6、 phase differenceaccessional light path difference等傾干涉條紋sin21ne2222nid+didididisoclinal interference fringeswhen the isoclinal incident rayare reflected by the film,the interference fringes with same orderiiiisf1n3n2nessii1n3n2neEliminating reflection:The least thickness for the coating is:SP36-5(p.

7、879) A glass lens is coasted on one side with a thin film of magnesium fluoride MgF2 to reduce reflection from the lens surface. What is the least coating thickness that eliminates (via interference) the reflections at the =550nm?Assume平行膜例一airoil filmglass1n3n2n15.01.41.2dmn50white lightinterferenc

8、e of reflected lightinterference of transmited light例1.which light can be constructive during reflectiong?2.which light can be constructive during transmittion?3. If the wavelength 550 nm is destructive during refection, what is the thickness of the oil film at least?Constructive interference of ref

9、lected lightd0+ddl2n2d+0kl2n2dkk1mn070l1k20mn35l2d0+dd242n2d+llkkln2d()21k2k13k6mn74l2l13lmn820mn4100Constructive interference of transmitted lightd0+dd2n2d+0k()21+l2d4n2k()21+ldmin4n2l.982nmk0l550,nmDestructive interference of reflected lightSMwedge三 Wedge-shape filmmaximumminimumInterference on th

10、e edge（bright fringe）（dark fringe）Discuss1）point of the edgeDark fringe.3）distance between adjacent fringes2）The thickness difference between two adjacent bright (or dark ) fringes. Interference on the edge Every fringe corresponds to the thickness of the edge. Thus when the thickness of one positio

11、n changes, the corresponding fringe will move. 4 ）The moving of the fringe 36-6(p.879) A transparent plastic block with a thin wedge of air at right. A broad beam of red light with =632.8nm, is directed downward through the top of the block. The interfere-nce pattern consists of six dark fringes and

12、 five bright red fringes. What is the change in thickness along the wedge?2）measuring thickness1）measuring expand The application of interference on wedge-shape filmair 3）Checking of optical elements level4）measuring the diameter of the filament四：Newtons ringsConsisting of a lens and a plane glass p

13、latePath difference Experimental apparatusRPath differencemaximumminimumrdradius of dark ringradius of bright ring4）Application: can be used to measure light wavelength, to test the quantity of the lenses. 1）View from the upper surface, whether the center is bright or dark? View from the lower surface, whether the center is dark or bright?2）why the distance betwe