chi2 map
illustrate resonant enhancements

Dres[ω_]:=((ω0)^2)-(ω^2)-I 2ω γ;
chi2[ω1_,ω2_]:=(1/(Dres[ω1]Dres[ω2]Dres[ω1+ω2]));

ω0=10;
γ=0.5`;
ωMax=15;
ContourPlot[Re[chi2[ω1,ω2]],{ω1,0,ωMax},{ω2,0,ωMax},Mesh->False,PlotPoints->100,ColorFunction->Hue,PlotRange->All,Contours->15]

Plot3D[Re[chi2[ω1,ω2]],{ω1,0,ωMax},{ω2,0,ωMax},Mesh->False,PlotPoints->100,PlotRange->All]

ωMax=25;
Plot3D[Abs[chi2[ω1,ω2]],{ω1,-ωMax,ωMax},{ω2,-ωMax,ωMax},Mesh->False,PlotPoints->100,PlotRange->All]

DensityPlot[Abs[chi2[ω1,ω2]],{ω1,-ωMax,ωMax},{ω2,-ωMax,ωMax},Mesh->False,PlotPoints->100,ColorFunction->Hue,PlotRange->All]