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import numpy as np
def fresnelReflection(n1, n2, thetaInc):
# 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 angle in medium 1 with respect to normal, could be a vector
# R - coefficients of reflection array [Rs, Rp]
# theta_t - transmitted/refracted angle in medium 2 with respect to normal
#if np.size(thetaInc, axis=0) != 1:
# error('thetaInc must be a vector or scalar')
# see http://en.wikipedia.org/wiki/Fresnel_equations
# refraction angle or angle of transmitted beam with respect to normal
sinThetaTrans = n1 / n2 * np.sin(thetaInc)
# special cases: total internal reflection
if abs(sinThetaTrans) >= 1:
sinThetaTrans = np.copysign(1, sinThetaTrans)
thetaTrans = np.arcsin(sinThetaTrans) # angle of refraction
cosThetaTrans = np.cos(thetaTrans)
cosThetaInc = np.cos(thetaInc)
Rs = ((n1 * cosThetaInc - n2 * cosThetaTrans) /\
(n1 * cosThetaInc + n2 * cosThetaTrans)) ** 2
Rp = ((n1 * cosThetaTrans - n2 * cosThetaInc) /\
(n1 * cosThetaTrans + n2 * cosThetaInc)) ** 2
R = np.array([[Rs], [Rp]])
return [R, thetaTrans]
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