Maximum diffraction efficiency as a function of angular miss match for a volume hologram

From Optical Imaging and Spectroscopy (Wiley - OSA 2009)
By David J. Brady
www.opticalimaging.org
Figure 4.23

K=2 Sin[Pi/6];
de=10^(-2);
kr[theta_]:={Sin[theta],Cos[theta]};
ks[theta_]:={kr[theta][[1]]-K,Sqrt[1-(kr[theta][[1]]-K)^2]};
dkz[theta_]:=kr[theta][[2]]-ks[theta][[2]];
gamma[theta_]:=Sqrt[dkz[theta]^2+de^2/(kr[theta][[2]] ks[theta][[2]])]/2;
eta[theta_]:=N[de^2/(4 ks[theta][[2]]^2 gamma[theta]^2)];

Plot[eta[theta],{theta,((3 π)/24),((5 π)/24)},PlotRange->All,Frame->True,Axes->False,FrameLabel->{Radians,Diffraction Efficiency}]