!(lambda = 6500. ; d = 10 lambda; n
  c = 3.  10^8; f = c/lambda; T = 1/f; omega = N[2 [Pi] f]; Eo = 1. ; 
  )

!(*
  RowBox[{"Do", "[", 
    RowBox[{
      RowBox[{
      (Theta = N[(n [Pi])/2]), ";", 
        (phi = N[(2 [Pi] d)/lambda] Sin[Theta]), ";", 
        RowBox[{(Int[n]), "=", 
          RowBox[{(1/10), " ", 
            RowBox[{
              UnderoverscriptBox["…", GridBox[{
                    {(t = 0)},
                    {([CapitalDelta][MediumSpace]t = T/10)}
                    }], (T - T/10)], 
              (((Eo Sin[omega t] + Eo Sin[omega t + phi]))^2
                  )}]}]}]}], ",", ({n, 0, 0.5, 0.005})}], "]"}])

!((data = Table[{N[(n [Pi])/2], Int[n]}, {n, 0, 0.5, 0.005}]; )n
  (ListPlot[data]; ))

ListPlot[data,PlotJoined[Rule]True,AxesLabel[Rule]{"Theta","Intensity"}];

!(*
  RowBox[{
  (lambda = 6500. ; d = 10 lambda; ), "n", (c = 3.  10^8; 
    f = c/lambda; T = 1/f; omega = N[2 [Pi] f]; Eo = 1. ; ), "n", 
    RowBox[{"Do", "[", 
      RowBox[{
        RowBox[{
        (Theta = N[(n [Pi])/2]), ";", 
          (phi = N[(2 [Pi] d)/lambda] Sin[Theta]), ";", 
          RowBox[{(Int[n]), "=", 
            RowBox[{(1/10), " ", 
              RowBox[{
                UnderoverscriptBox["…", GridBox[{
                      {(t = 0)},
                      {([CapitalDelta][MediumSpace]t = T/10)}
                      }], (T - T/10)], 
                (((Eo Sin[omega t] + Eo Sin[omega t + phi] + 
                      Eo Sin[omega t + 2 phi]))^2)}]}]}]}], ",", 
        ({n, 0, 0.25, 0.0025})}], "]"}]}])

!((data = Table[{N[(n [Pi])/2], Int[n]}, {n, 0, 0.25, 0.0025}]; )n
  (ListPlot[data, PlotJoined [Rule] True, 
    AxesLabel [Rule] {"<Theta>", "<Intensity>"}]; ))

!(*
  RowBox[{
  (lambda = 6500. ; d = 10 lambda; ), "n", (c = 3.  10^8; 
    f = c/lambda; T = 1/f; omega = N[2 [Pi] f]; Eo = 1. ; ), "n", 
    RowBox[{"Do", "[", 
      RowBox[{
        RowBox[{
        (Theta = N[(n [Pi])/2]), ";", 
          (phi = N[(2 [Pi] d)/lambda] Sin[Theta]), ";", 
          RowBox[{(Int[n]), "=", 
            RowBox[{(1/10), " ", 
              RowBox[{
                UnderoverscriptBox["…", GridBox[{
                      {(t = 0)},
                      {([CapitalDelta][MediumSpace]t = T/10)}
                      }], (T - T/10)], 
                (((Eo (…+(k = 0)%3 Sin[omega t + k phi])))^2
                    )}]}]}]}], ",", ({n, 0, 0.1, 0.001})}], "]"}]}])

!((data = Table[{N[(n [Pi])/2], Int[n]}, {n, 0, 0.1, 0.001}]; )n
  (ListPlot[data, PlotJoined [Rule] True, 
    AxesLabel [Rule] {"<Theta>", "<Intensity>"}]; ))

!(*
  RowBox[{
  (lambda = 6500. ; d = 10 lambda; ), "n", (c = 3.  10^8; 
    f = c/lambda; T = 1/f; omega = N[2 [Pi] f]; Eo = 1. ; ), "n", 
    RowBox[{"Do", "[", 
      RowBox[{
        RowBox[{
        (Theta = N[(n [Pi])/2]), ";", 
          (phi = N[(2 [Pi] d)/lambda] Sin[Theta]), ";", 
          RowBox[{(Int[n]), "=", 
            RowBox[{(1/10), " ", 
              RowBox[{
                UnderoverscriptBox["…", GridBox[{
                      {(t = 0)},
                      {([CapitalDelta][MediumSpace]t = T/10)}
                      }], (T - T/10)], 
                (((Eo (…+(k = 0)%9 Sin[omega t + k phi])))^2
                    )}]}]}]}], ",", ({n, 0, 0.1, 0.0005})}], "]"}]}])

!((data = Table[{N[(n [Pi])/2], Int[n]}, {n, 0, 0.1, 0.0005}]; )n
  (ListPlot[data, PlotRange [Rule] All, PlotJoined [Rule] True, 
    AxesLabel [Rule] {"<Theta>", "<Intensity>"}]; ))