Hình:Two-Slit Diffraction.png
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This is a drawing explaining two-slit diffraction: Planar wavefronts with wavelength λ (straight, vertical blue lines in the left-hand side of the image) arrives from the left at a barrier (thick yellow line) which have two slits or holes in it, at a distance d from each other. On the right-hand side of the barrier, the circular wavefronts that "leak" through the slits interfere with one another. This causes the light to scatter so that in certain directions, called orders (gray arrows labeled m0, m1, and m2), the light "concentrates" in beams while little or no light is emitted in the directions in between these orders.
This image was rendered using the Persistence Of Vision Raytracer (POV-Ray for short) and the image description below. Note that to render this image, your POV-Ray installation needs to have access to the TrueType™ fonts timesbi.ttf (Times New Roman, bold & italic), timesbd.ttf (Times New Roman, bold), and symbols.ttf (various symbols, including greek letters), in order to render the white letters and numbers shown in the image.
[edit] Image description for use in POV-Ray
/* ================================================ Two-Slit Diffraction ------------------------------------------------ Created by Søren Peo Pedersen - see my user page at http://da.wikipedia.org/wiki/Bruger:Peo ================================================ */ #declare WavefrontColor=<.2,.4,1>; // Wavefronts (default: blue) #declare BarrierColor=<1,.8,.2>; // Barrier (default: Yellow) union { // The barrier with two slits in it: box {<-.1,.6,-.01>,<.1,5,.01>} // Part above the slits box {<-.1,-.4,-.01>,<.1,+.4,.01>} // Part between the slits box {<-.1,-5,-.01>,<.1,-.6,.01>} // Part below the slits pigment {color rgb BarrierColor} finish {ambient 1} } #local Cnt=1; // Loop that puts some wavefront lines #while (Cnt<5) // to the left of the barrier cylinder {<(.5-Cnt)*0.37,-5,0>,<(.5-Cnt)*0.37,5,0>,.02 pigment {color rgb WavefrontColor} finish {ambient 1}} #local Cnt=Cnt+1; #end // Arrows to indicate the directions of diffraction orders: #macro OrderArrow(Start,End,Direction) // Macro to render one arrow union { triangle {<End,0,.01>,<End-1,-.3,.01>,<End-1,.3,.01>} // Forms an arrow triangle {<End-1,-.1,.01>,<End-1,.1,.01>,<Start,.1,.01>} // stretching from triangle {<End-1,-.1,.01>,<Start,.1,.01>,<Start,-.1,.01>} // Start to End a- pigment {color rgb .6} // long the +X ax- finish {ambient 1} // is, then turns rotate <0,0,Direction> // it to Direction } #end // Use the above macro to indicate 0th thru 2nd order diffraction: #object {OrderArrow(1.3,3.3,47.73141557)} // 2nd order upwards #object {OrderArrow(1,5.7,21.71561728)} // 1st order upwards #object {OrderArrow(.5,5.4,0)} // 0th order horizontal #object {OrderArrow(1,5.7,-21.71561728)} // 1st order downwards #object {OrderArrow(1.3,3.3,-47.73141557)} // 2nd order downwards // "m=(number)" legends at each diffraction order #macro Mlig(Number) // Macro to render "m=" in bold italic, followed union { // by the given Number in bold non-italic text {ttf "timesbi.ttf" "m=",.01,0} text {ttf "timesbd.ttf" str(Number,0,0),.01,0 translate <1.4,0,0>} pigment {color rgb 1} finish {ambient 1} scale .6 translate <0,0,-.2> } #end // Use the above macro to label each order of diffraction: #object {Mlig(2) translate <.3,1.95,0>} // 2nd opder upwards #object {Mlig(1) translate <3.1,1.8,0>} // 1st order upwards #object {Mlig(0) translate <4,-.65,0>} // 0th order #object {Mlig(1) translate <3.1,-2.1,0>} // 1st order downwards #object {Mlig(2) translate <.3,-2.3,0>} // 2nd order downwards // Angle-measuring "arcs" to indicate angles of diffraction: #macro Angle(Degrees,Index,Radius) union { difference { // The arc part: cylinder {<0,0,-.1>,<0,0,-.11>,Radius} // A cylinder, whose cur- plane {<0,Degrees,0>,0} // ved surface defines the plane {<0,-Degrees,0>,0 rotate <0,0,Degrees>} // arc, then parts of it pigment { // are cut away using pla- cylindrical // ne. Then it gets a cy- color_map { // lindrical pigment thats [0 color rgbt <1,1,1,0.5>] // transparent at the cen- [0.2 color rgbt <1,1,1,0.75>] // ter so you only see it [1 color rgbt <1,1,1,1.0>] // out near the curved } // part. rotate <90,0,0> scale Radius } finish {ambient 1} } union { // "Nametag"; Greek "theta" with the given Index number: text {ttf "symbol.ttf","q",0.1,0 pigment {color rgb 1} finish {ambient 1} scale .6 translate <-.2,-.2,0>} text {ttf "timesbd.ttf",str(Index,0,0),0.1,0 pigment {color rgb 1} finish {ambient 1} scale .4 translate <.1,-.3,0>} translate <(Radius+.3)*cos(radians(Degrees/2)),(Radius+.3)*sin(radians(Degrees/2)),-.2> } } #end // Use the above macro to indicate the angles of diffraction: #object {Angle( 21.71561728,1,3)} // Show 1st order diffraction angle upwards #object {Angle(-47.73141557,2,1.6)} // Show 2nd order diffraction angle downwards #local Hole=-.5; // Loop run twice; once for #while (Hole<1) // each slit in the barrier. box {<-.6,Hole-.02,-.2>,<-.2,Hole+.02,-.1> // Little lines and pigment {color rgb 1} finish {ambient 1} // triangular arrow- } // heads showing the triangle { // distance between <-.5,Hole*.98,-.2>,<-.4,Hole*.5,-.2>,<-.6,Hole*.5,-.2> // the two slits in pigment {color rgb 1} finish {ambient 1} // the barrier. } #local Cnt=1; // Loop run "several" (20) times to render concentric #while (Cnt<20) // wavefronts emanating from each slit in the barrier: difference { torus {(Cnt-.5)*0.37,.02} // Torus to form the arc, minus a plane to plane {<1,0,0>,.1} // cut away part of arc left of the barrier pigment {color rgb WavefrontColor} finish {ambient 1} rotate <90,0,0> translate <0,Hole,0> } #local Cnt=Cnt+1; #end #local Hole=Hole+1; #end union { // Various letters and arrowheads: text {ttf "timesbi.ttf","d",0.1,0 // The "d" representing the distance scale .6 translate <-.66,-.2,-.2>} // between the slits in the barrier text {ttf "symbol.ttf","l",0.1,0 // Greek letter "lambda" representing scale .6 translate <-.89,1.5,-.2>} // the wavelength triangle {<-0.525,1.7,0>,<-0.325,1.6,0>,<-0.325,1.8,0>} // Arrowheads left and triangle {<-0.955,1.7,0>,<-1.155,1.6,0>,<-1.155,1.8,0>} // right of "lambda" pigment {color rgb 1} finish {ambient 1} } camera { // Viewpoint: orthographic // No perspective location <2.1,0,-5> // Looking from this position look_at <2.1,0,0> // Looking towards this position }
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