\[Lambda] = 1;
k0 = (2 \[Pi])/\[Lambda];
G[r_] := I/4 HankelH1[0, k0 Norm[r] ];
s = Table[{h,(Abs[NIntegrate[G[{Cos[\[Theta]], Sin[\[Theta]]}] - G[{Cos[\[Theta]], Sin[\[Theta]]} - {2*h, 0}], {\[Theta], 0, 2 \[Pi]}] ]/s0)^2}, {h, 3, 0, -0.01}];
p1 = Table[
   GraphicsRow[{
DensityPlot[Abs[G[{x, y}] - G[{x + 2*h, y}] ]^2, {x, -3, 7}, {y, -5, 5}, PlotPoints -> 100, Frame -> False, ColorFunction -> "AvocadoColors", PlotLabel -> "|E\!\(\*SuperscriptBox[\(|\), \(2\)]\)", 
      PlotRange -> {0, 0.02}, LabelStyle -> {Black, Bold}, Epilog -> {Gray, Polygon[{{-5, -5}, {-h, -5}, {-h, 5}, {-5, 5}}]}]
     ,
     ListPlot[s, PlotRange -> {0, 2}, Joined -> True, Axes -> False, Frame -> True, LabelStyle -> {Black, Bold}, PlotStyle -> {Black, Thick}, FrameLabel -> {"Distance from the mirror / \[Lambda]", 
        "P/\!\(\*SubscriptBox[\(P\), \(\[Infinity]\)]\)"}, Epilog -> {PointSize[0.03], Red, Point[{h, Evaluate[(1/s0 Abs[NIntegrate[G[{Cos[\[Theta]], Sin[\[Theta]]}] - G[{Cos[\[Theta]], Sin[\[Theta]]} - {2*h, 0}], {\[Theta], 0, 2 \[Pi]}] ])^2]}]}]
     }, ImageSize -> Large]
   , {h, 3, 0, -0.05}];
ListAnimate[p1]

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