/*
 ================================================
 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
   }