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function [R, theta_t] = fresnel_reflection(n1, n2, theta_i)
%% calculates intensity reflection coefficient for s and p polarizations
%% for light travelling from material with index of refraction n1 to material with n2
%% theta_i - incident index of refraction
%% R - coefficients of reflection array [Rs, Rp]
%% see http://en.wikipedia.org/wiki/Fresnel_equations
%% refracstion angle or angle of transmitted beam with respect to normal
sin_theta_t=n1/n2*sin(theta_i);
if ( abs(sin_theta_t) >= 1)
%% total internal reflection
R = [1, 1];
theta_t=sign(theta_i)*pi/2;
return;
end
theta_t = asin(sin_theta_t); % angle of refraction or transmitted beam
cos_theta_t = cos( theta_t );
cos_theta_i = cos( theta_i );
Rs = ( ( n1*cos_theta_i - n2*cos_theta_t ) / ( n1*cos_theta_i + n2*cos_theta_t ) ).^2;
Rp = ( ( n1*cos_theta_t - n2*cos_theta_i ) / ( n1*cos_theta_t + n2*cos_theta_i ) ).^2;
R = [Rs,Rp];
end
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