# Overlay for two axes plot

I have these two plots that I want to merge in order to create a plot with two axes. I just want to translate the second plot in order for them precisely coincide. However, it seems that the Translate command does not work for plots. How can I make the plots coincide?

Thanks!

lambda=18.0;

dataIL={{0*lambda,-7.919},{10*lambda,-8.274},{50*lambda,-9.381},{100*lambda,-11.193},{200*lambda,-14.969}};

fitIL=Transpose[{Table[x,{x,0,200*lambda,lambda}],Table[-7.810743628185908-0.001957142262202232 x,{x,0,200*lambda,lambda}]}];

dataGD={{0*lambda,0.03849},{10*lambda,0.05877},{50*lambda,0.1597},{100*lambda,0.2843},{200*lambda,0.5677}};

fitGD=Transpose[{Table[x,{x,0,200*lambda,lambda}],Table[0.03100392803598201 +0.00014721301849075468 x,{x,0,200*lambda,lambda}]}];

Overlay[{a,b}]


A starting point:

lambda=18.0;
dataIL={{0*lambda,-7.919},{10*lambda,-8.274},{50*lambda,-9.381},{100*lambda,-11.193},{200*lambda,-14.969}};
fitIL=Transpose[{Table[x,{x,0,200*lambda,lambda}],Table[-7.810743628185908-0.001957142262202232 x,{x,0,200*lambda,lambda}]}];
dataGD={{0*lambda,0.03849},{10*lambda,0.05877},{50*lambda,0.1597},{100*lambda,0.2843},{200*lambda,0.5677}};
fitGD=Transpose[{Table[x,{x,0,200*lambda,lambda}],Table[0.03100392803598201 +0.00014721301849075468 x,{x,0,200*lambda,lambda}]}];
a=ListPlot[{dataIL,fitIL},PlotRange->All,Frame->{{True,False},{True,True}},FrameTicks -> {{All, None}, {All,None}},ImagePadding ->20];
b=ListPlot[{dataGD,fitGD},PlotRange->All,Frame->{{False,True},{False,False}},FrameTicks -> {{None, All}, {None, None}},ImagePadding ->20];
Overlay[{a,b}]


Output: