SetDirectory[NotebookDirectory[]]

sol=FullSimplify[Solve[{
AI+AR==αI+αR,
αI Exp[-ξ d]+αR Exp[ξ d]==AT Exp[I k d],
I k AI-I k AR==-ξ αI+ξ αR,
-ξ αI Exp[-ξ d]+αR ξ Exp[ξ d]==I k AT Exp[I k d]},
{AR, AT, αR, αI}]]

Ar=Manipulate[Plot[Abs[AR/.sol{1}/.{AI->1,k->n k0 Cos[θ],ξ->k0 (Sqrt[(n^2) ((Sin[θ])^2)-1])}/.{k0->1,n->1.5}],{d,0,20},PlotRange->{0,1}],{θ,0,Pi/2}]

AvsD=Manipulate[Plot[ Re[(AI Exp[I k z]+AR Exp[-I k z]) HeavisideTheta[-z]+
(αI Exp[-ξ z]+αR Exp[ξ z])HeavisideTheta[d-z] HeavisideTheta[z]+
AT Exp[I k z]HeavisideTheta[z-d]]/.sol{1}/.{AI->1,k->n k0 Cos[θ],ξ->k0 (Sqrt[(n^2) ((Sin[θ])^2)-1])}/.{n->1.5,θ->θ1,d->d1},{z,-20,20}],{d1,0,15}, {θ1,0,Pi/2},{k0,0.2,5}]

Manipulate[Plot[ Re[(AI Exp[I k z]+AR Exp[-I k z]) HeavisideTheta[-z]+
(αI Exp[-ξ z]+αR Exp[ξ z])HeavisideTheta[d-z] HeavisideTheta[z]+
AT Exp[I k z]HeavisideTheta[z-d]]/.sol{1}/.{AI->1,k->n k0 Cos[θ],ξ->k0 (Sqrt[(n^2) ((Sin[θ])^2)-1])}/.{n->1.5,θ->θ1,d->d1},{z,-20,20}],{d1,0,15}, {θ1,0,Pi/2},{k0,0.2,5}]

abs=Manipulate[Plot[ Abs[(AI Exp[I k z]+AR Exp[-I k z]) HeavisideTheta[-z]+
(αI Exp[-ξ z]+αR Exp[ξ z])HeavisideTheta[d-z] HeavisideTheta[z]+
AT Exp[I k z]HeavisideTheta[z-d]]^2/.sol{1}/.{AI->1,k->n k0 Cos[θ],ξ->k0 (Sqrt[(n^2) ((Sin[θ])^2)-1])}/.{n->1.5,θ->θ1,d->d1},{z,-20,20},PlotRange->{0,5}],{d1,0,15}, {θ1,0,Pi/2},{k0,0.2,5}]