d = 0.25/2;
r = 73.8;
s = 180;
\[Lambda] = 632.8*10^-6;
\[Alpha] = Sqrt[2*(1/r + 1/s)/\[Lambda]];
\[Beta] = r/(r + s);
DensityPlot[(- FresnelS[ \[Alpha]*(\[Beta]*x - d)] + 
     FresnelS[\[Alpha]* (\[Beta]*x + d)])^2 + (- 
      FresnelC[\[Alpha]* (\[Beta]*x - d)] + 
     FresnelC[ \[Alpha]*(\[Beta]*x + d)])^2, {x, -3, 3}, {y, 0, 20}, 
 PlotPoints -> 100]

ParametricPlot[{x = t, 
  y = ((- FresnelS[ \[Alpha]*(\[Beta]*x - d)] + 
        FresnelS[\[Alpha]* (\[Beta]*x + d)])^2 + (- 
         FresnelC[\[Alpha]* (\[Beta]*x - d)] + 
        FresnelC[ \[Alpha]*(\[Beta]*x + d)])^2)}, {t, -2.4, 2}, 
 PlotRange -> Full, AspectRatio -> 0.5]

ParametricPlot[{x = t, 
  y = (- FresnelS[(x)] - 0.5)^2 + 
    0.5 (- FresnelC[ (x)] - 0.5)^2}, {t, -3, 5}, PlotRange -> Full]
    
 ParametricPlot[{x = t, 
  y = (- FresnelS[(x)] - 0.5)^2 + 
    0.5 (- FresnelC[ (x)] - 0.5)^2}, {t, -3, 5}, PlotRange -> Full]