%% document on the Op-Lev for KAGRA
clc
clear all
close all
format long

%% Normalized sensitivity as function of the beam radius (ref. APPLIED OPTICS / Vol. 53, No. 13)

w = logspace(-2,2,1000)*10^(-3);
b=100e-6;
a=3.9e-3;


S = (2*erf(sqrt(2)*a./w)-2*erf(sqrt(2)*b./w)).*sqrt(2/pi)./w.*(exp(-2*(a./w).^2)-exp(-2*(b./w).^2));

figure
loglog(w*10^3,-S/1e3)
axis([0.01 30 0.01 30])
hold on

b=15e-6;
a=10e-3/2-b;
S = (2*erf(sqrt(2)*a./w)-2*erf(sqrt(2)*b./w)).*sqrt(2/pi)./w.*(exp(-2*(a./w).^2)-exp(-2*(b./w).^2));

loglog(w*10^3,-S/1e3)
grid on
hold off
legend('ref. APPLIED OPTICS / Vol. 53, No. 13','KAGRA oplev, a=4.985mm, b=15um')



