dielectric_stack.py

# -*- coding: utf-8 -*-
"""
Created on Tue Oct 24 14:17:58 2017

@author: Chronum
"""

import numpy as np
import matplotlib.pyplot as plt

def filmstack_reflectivities(rix_array, film_thickness_array, wavelengths,
                             theta = 0, polarization = 'te'):
    num_layers = len(film_thickness_array)
    if num_layers != len(rix_array)-2: # Rix array has 2 extra rix values.
        print("Error!: Array of layer thickness must have 2 fewer v"
              "alues than array of rix values.")
        raise IndexError
        
    layer_cos_projection = np.sqrt(1-(rix_array[0]/rix_array*np.sin(theta))**2)
    if polarization.lower() == 'te':
        effective_rix_array = rix_array*layer_cos_projection
    else:
        effective_rix_array = rix_array/layer_cos_projection
        
    effective_film_thickness = film_thickness_array*layer_cos_projection[1:-1]
    
    fresnel_coeff_array = np.diff(effective_rix_array)/\
                        (effective_rix_array[0:-1]+effective_rix_array[1:])
            
    reflectivity = fresnel_coeff_array[-1]*np.ones_like(wavelengths)
    
    for j in range(num_layers-1, -1, -1):
        phase_exponent = 2*np.pi*effective_film_thickness[j]/wavelengths
        phase_shift = np.exp(2j*phase_exponent)
        reflectivity = (fresnel_coeff_array[j]+reflectivity*phase_shift)/\
                        (1+fresnel_coeff_array[j]*reflectivity*phase_shift)
    return reflectivity
    
    

rixes = np.array([1, 1.4, 1.6, 1.9, 1.6, 1.4, 1.6, 1.9, 1.6, 1.4, 1])
lens = np.array([1, 1, 1, 1, 1.0, 9, 1, 1, 1])
wlens = np.linspace(1.2, 1.6, 1000)
# plt.plot(rixes)
refl = filmstack_reflectivities(rixes, lens, wlens)
plt.plot(wlens, -refl)