aa[w_,b_,w0_] := 1/((w0^2-w^2)^2+4 b^2*w^2)

Plot[aa[w,.1,1],{w,0,3},PlotRange -> {0,30},AxesLabel->None, PlotStyle -> Thick]

Plot[{aa[w,.1,1],aa[w,.2,1]},{w,0,3}, PlotRange -> {0,30}]

Plot[{aa[1,.1,w],aa[1,.2,w]},{w,0,3}, PlotRange -> {0,30}]