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#!/usr/bin/env python3
"""
Plot the scattering cross section as a function of wavelength for 100nm gold spheres
"""
import numpy as np
import matplotlib.pyplot as plt
import miepython
# from https://refractiveindex.info/?shelf=main&book=Au&page=Johnson
# wavelength in microns
ref_lam=np.array([0.1879,0.1916,0.1953,0.1993,0.2033,0.2073,0.2119,0.2164,0.2214,0.2262,0.2313,0.2371,0.2426,0.2490,0.2551,0.2616,0.2689,0.2761,0.2844,0.2924,0.3009,0.3107,0.3204,0.3315,0.3425,0.3542,0.3679,0.3815,0.3974,0.4133,0.4305,0.4509,0.4714,0.4959,0.5209,0.5486,0.5821,0.6168,0.6595,0.7045,0.7560,0.8211,0.8920,0.9840,1.0880,1.2160,1.3930,1.6100,1.9370])
ref_n=np.array([1.28,1.32,1.34,1.33,1.33,1.30,1.30,1.30,1.30,1.31,1.30,1.32,1.32,1.33,1.33,1.35,1.38,1.43,1.47,1.49,1.53,1.53,1.54,1.48,1.48,1.50,1.48,1.46,1.47,1.46,1.45,1.38,1.31,1.04,0.62,0.43,0.29,0.21,0.14,0.13,0.14,0.16,0.17,0.22,0.27,0.35,0.43,0.56,0.92])
ref_k=np.array([1.188,1.203,1.226,1.251,1.277,1.304,1.350,1.387,1.427,1.460,1.497,1.536,1.577,1.631,1.688,1.749,1.803,1.847,1.869,1.878,1.889,1.893,1.898,1.883,1.871,1.866,1.895,1.933,1.952,1.958,1.948,1.914,1.849,1.833,2.081,2.455,2.863,3.272,3.697,4.103,4.542,5.083,5.663,6.350,7.150,8.145,9.519,11.21,13.78])
radius = 0.1 # in microns
num = len(ref_lam)
m = ref_n-1.0j*ref_k
x = 2*np.pi*radius/ref_lam
qqabs = np.zeros(num)
qqsca = np.zeros(num)
for i in range(num) :
qext, qsca, qback, g = miepython.mie(m[i],x[i])
qabs = qext - qsca
qqabs[i]=qabs*np.pi*radius**2
qqsca[i]=qsca*np.pi*radius**2
plt.plot(ref_lam*1000, qqabs, color='blue')
plt.plot(ref_lam*1000, qqsca, color='red')
plt.title(r"Gold Spheres 100nm diameter")
plt.xlabel("Wavelength (nm)")
plt.ylabel(r"Cross Section ($\mu$m$^2$)")
plt.annotate("absorption", xy=(700,0.01), color='blue')
plt.annotate("scattering", xy=(750,0.1), color='red')
plt.show()