mirrors.tex

\documentclass[tikz,border=24pt]{standalone}

\usetikzlibrary{patterns,calc,decorations.markings,arrows}
\usepackage{tkz-euclide}
\usetkzobj{all}
\tikzset{
  ray/.style={
    dashed,
  },
  ray segment/.style={
    ray,
    postaction=decorate,
    decoration={
      markings,
      mark=at position .5 with {\arrow[thick]{stealth}}
    }
  },
  ray terminator/.style={
    ray,
    -stealth,
  },
}

\begin{document}

\begin{tikzpicture}[scale=6]
  % Coordinate system origin
  \tkzDefPoint(0,0){O};
  % Source of the ray
  \tkzDefPoint(0.9063,0.8452){start};
  % Point of intersection of the ray with the first mirror
  \tkzDefPoint(0,0.4226){P};
  \tkzDefPoint(-0.1,0.4226){Pleft};
  \tkzDefPoint(0.25,0.4226){Pright};
  \tkzDefMidPoint(O,P);
  \tkzGetPoint{MA};
  % Intersection of the ray with the second mirror, plus normals
  \tkzDefPoint(0.9063,0){Q};
  \tkzDefPoint(0.9063,0.25){Qup};
  \tkzDefMidPoint(O,Q);
  \tkzGetPoint{MB};
  % Extensions of the axis
  \tkzDefPoint(0,1){vertical};
  \tkzDefPoint(1.5,0){horizontal};
  % Intersection of the ray with the water, plus normals
  \tkzDefPoint(1.5,0.2768){hit};
  \tkzDefPoint(1.2,0.2768){hitleft};
  \tkzDefPoint(1.8,0.2768){hitright};
  % Refraction vector of the ray
  \tkzDefPoint(1.8865,0.3797){refract};
  % Quadrilateral delimiters for the water
  \tkzDefPoint(1.5,0.75){waterne};
  \tkzDefPoint(2,0.75){waternw};
  \tkzDefPoint(2,0){watersw};
  % Coordinates and water drawing
  \tkzDrawSegments(O,vertical O,horizontal);
  \tkzLabelPoint[right](vertical){air ($n = 1$)};
  \tkzFillPolygon[blue,fill opacity=0.15](horizontal,waterne,waternw,watersw);
  \tkzLabelPoint[above right](waterne){water ($n' = 1.33$)};
  % Mirror drawing
  \tkzDrawSegments[ultra thick](O,P O,Q);
  \tkzLabelPoint[left](MA){Mirror~A};
  \tkzLabelPoint[below](MB){Mirror~B};
  % Normal drawing
  \tkzDrawSegment[dotted](Pleft,Pright);
  \tkzDrawSegment[dotted](Q,Qup);
  \tkzDrawSegment[dotted](hitleft,hitright);
  % Intersection points
  \tkzLabelPoint[above left](P){$P$};
  \tkzLabelPoint[below](Q){$Q$};
  \tkzLabelPoint[above left](hit){$R$};
  % Light ray drawing
  \tkzDrawSegments[ray segment](start,P P,Q Q,hit);
  \tkzDrawSegment[ray terminator](hit,refract);
  % The following angle commands extend the bounding box unnecessarily
  % (by calculating the extension of the relevant arcs to full circles).
  % Save the current bounding box and fix it.
  \useasboundingbox (current bounding box.north east) rectangle (current bounding box.south west);
  %% All theta-equivalent angles
  \tkzMarkAngles[fill=yellow,fill opacity=0.25,size=0.2,mark=|](Pright,P,start Q,P,Pright P,Q,O horizontal,Q,hit hitleft,hit,Q);
  \tkzLabelAngles[pos=0.25](Pright,P,start Q,P,Pright P,Q,O horizontal,Q,hit){$\theta$};
  %%% (this one's weird and inverted for some reason)
  \tkzLabelAngles[pos=-0.25](hitleft,hit,Q){$\theta$};
  %% All phi-equivalent angles
  \tkzMarkAngles[fill=red,fill opacity=0.25,size=0.15,mark=||](O,P,Q Q,hit,horizontal Qup,Q,P hit,Q,Qup);
  \tkzLabelAngles[pos=0.225,mark=||](O,P,Q Q,hit,horizontal Qup,Q,P hit,Q,Qup){$\phi$};
  %% The desired angle
  \tkzMarkAngle[fill=blue,fill opacity=0.25,size=0.15](hitright,hit,refract);
  \tkzLabelAngle[pos=0.3](hitright,hit,refract){$\theta'$};
  %% All right angles
  \tkzMarkRightAngles[size=0.050](Q,O,P watersw,horizontal,waterne);
  % Draw intersection points last (otherwise segments are above)
  \tkzDrawPoints(P,Q,hit);
\end{tikzpicture}

\end{document}