# Source code for tmm.examples

```# -*- coding: utf-8 -*-
"""
Examples of plots and calculations using the tmm package.
"""

from __future__ import division, print_function, absolute_import

from .tmm_core import (coh_tmm, unpolarized_RT, ellips,
position_resolved, find_in_structure_with_inf)

from numpy import pi, linspace, inf, array
from scipy.interpolate import interp1d
import matplotlib.pyplot as plt

try:
import colorpy.illuminants
import colorpy.colormodels
from . import color
colors_were_imported = True
except ImportError:
# without colorpy, you can't run sample5(), but everything else is fine.
colors_were_imported = False

# "5 * degree" is 5 degrees expressed in radians
# "1.2 / degree" is 1.2 radians expressed in degrees
degree = pi/180

[docs]def sample1():
"""
Here's a thin non-absorbing layer, on top of a thick absorbing layer, with
air on both sides. Plotting reflected intensity versus wavenumber, at two
different incident angles.
"""
# list of layer thicknesses in nm
d_list = [inf, 100, 300, inf]
# list of refractive indices
n_list = [1, 2.2, 3.3+0.3j, 1]
# list of wavenumbers to plot in nm^-1
ks = linspace(0.0001, .01, num=400)
# initialize lists of y-values to plot
Rnorm = []
R45 = []
for k in ks:
# For normal incidence, s and p polarizations are identical.
# I arbitrarily decided to use 's'.
Rnorm.append(coh_tmm('s', n_list, d_list, 0, 1/k)['R'])
R45.append(unpolarized_RT(n_list, d_list, 45*degree, 1/k)['R'])
kcm = ks * 1e7 #ks in cm^-1 rather than nm^-1
plt.figure()
plt.plot(kcm, Rnorm, 'blue', kcm, R45, 'purple')
plt.xlabel('k (cm\$^{-1}\$)')
plt.ylabel('Fraction reflected')
plt.title('Reflection of unpolarized light at 0\$^\circ\$ incidence (blue), '
'45\$^\circ\$ (purple)')

[docs]def sample2():
"""
Here's the transmitted intensity versus wavelength through a single-layer
film which has some complicated wavelength-dependent index of refraction.
(I made these numbers up, but in real life they could be read out of a
graph / table published in the literature.) Air is on both sides of the
film, and the light is normally incident.
"""
#index of refraction of my material: wavelength in nm versus index.
material_nk_data = array([[200, 2.1+0.1j],
[300, 2.4+0.3j],
[400, 2.3+0.4j],
[500, 2.2+0.4j],
[750, 2.2+0.5j]])
material_nk_fn = interp1d(material_nk_data[:,0].real,
d_list = [inf, 300, inf] #in nm
lambda_list = linspace(200, 750, 400) #in nm
T_list = []
for lambda_vac in lambda_list:
n_list = [1, material_nk_fn(lambda_vac), 1]
T_list.append(coh_tmm('s', n_list, d_list, 0, lambda_vac)['T'])
plt.figure()
plt.plot(lambda_list, T_list)
plt.xlabel('Wavelength (nm)')
plt.ylabel('Fraction of power transmitted')
plt.title('Transmission at normal incidence')

[docs]def sample3():
"""
Here is a calculation of the psi and Delta parameters measured in
ellipsometry. This reproduces Fig. 1.14 in Handbook of Ellipsometry by
Tompkins, 2005.
"""
n_list = [1, 1.46, 3.87+0.02j]
ds = linspace(0, 1000, num=100) #in nm
psis = []
Deltas = []
for d in ds:
e_data = ellips(n_list, [inf, d, inf], 70*degree, 633) #in nm
psis.append(e_data['psi']/degree) # angle in degrees
Deltas.append(e_data['Delta']/degree) # angle in degrees
plt.figure()
plt.plot(ds, psis, ds, Deltas)
plt.xlabel('SiO2 thickness (nm)')
plt.ylabel('Ellipsometric angles (degrees)')
plt.title('Ellipsometric parameters for air/SiO2/Si, varying '
'SiO2 thickness.\n'
'@ 70\$^\circ\$, 633nm. '
'Should agree with Handbook of Ellipsometry Fig. 1.14')

[docs]def sample4():
"""
Here is an example where we plot absorption and Poynting vector
as a function of depth.
"""
d_list = [inf, 100, 300, inf] #in nm
n_list = [1, 2.2+0.2j, 3.3+0.3j, 1]
th_0 = pi/4
lam_vac = 400
pol = 'p'
coh_tmm_data = coh_tmm(pol, n_list, d_list, th_0, lam_vac)

ds = linspace(-50, 400, num=1000) #position in structure
poyn = []
absor = []
for d in ds:
layer, d_in_layer = find_in_structure_with_inf(d_list, d)
data = position_resolved(layer, d_in_layer, coh_tmm_data)
poyn.append(data['poyn'])
absor.append(data['absor'])
# convert data to numpy arrays for easy scaling in the plot
poyn = array(poyn)
absor = array(absor)
plt.figure()
plt.plot(ds, poyn, 'blue', ds, 200*absor, 'purple')
plt.xlabel('depth (nm)')
plt.ylabel('AU')
plt.title('Local absorption (purple), Poynting vector (blue)')

[docs]def sample5():
"""
Color calculations: What color is a air / thin SiO2 / Si wafer?
"""
if not colors_were_imported:
print('Colorpy was not detected (or perhaps an error occurred when',
'Original version is at http://pypi.python.org/pypi/colorpy',
'A Python 3 compatible edit is at https://github.com/fish2000/ColorPy/')
return

# Crystalline silicon refractive index. Data from Palik via
# http://refractiveindex.info, I haven't checked it, but this is just for
# demonstration purposes anyway.
Si_n_data = [[400, 5.57 + 0.387j],
[450, 4.67 + 0.145j],
[500, 4.30 + 7.28e-2j],
[550, 4.08 + 4.06e-2j],
[600, 3.95 + 2.57e-2j],
[650, 3.85 + 1.64e-2j],
[700, 3.78 + 1.26e-2j]]
Si_n_data = array(Si_n_data)
Si_n_fn = interp1d(Si_n_data[:,0], Si_n_data[:,1], kind='linear')
# SiO2 refractive index (approximate): 1.46 regardless of wavelength
SiO2_n_fn = lambda wavelength : 1.46
# air refractive index
air_n_fn = lambda wavelength : 1

n_fn_list = [air_n_fn, SiO2_n_fn, Si_n_fn]
th_0 = 0

# Print the colors, and show plots, for the special case of 300nm-thick SiO2
d_list = [inf, 300, inf]
reflectances = color.calc_reflectances(n_fn_list, d_list, th_0)
illuminant = colorpy.illuminants.get_illuminant_D65()
spectrum = color.calc_spectrum(reflectances, illuminant)
color_dict = color.calc_color(spectrum)
print('air / 300nm SiO2 / Si --- rgb =', color_dict['rgb'], ', xyY =', color_dict['xyY'])
plt.figure()
color.plot_reflectances(reflectances,
title='air / 300nm SiO2 / Si -- '
'Fraction reflected at each wavelength')
plt.figure()
color.plot_spectrum(spectrum,
title='air / 300nm SiO2 / Si -- '
'Reflected spectrum under D65 illumination')

# Calculate irgb color (i.e. gamma-corrected sRGB display color rounded to
# integers 0-255) versus thickness of SiO2
max_SiO2_thickness = 600
SiO2_thickness_list = linspace(0, max_SiO2_thickness, num=80)
irgb_list = []
for SiO2_d in SiO2_thickness_list:
d_list = [inf, SiO2_d, inf]
reflectances = color.calc_reflectances(n_fn_list, d_list, th_0)
illuminant = colorpy.illuminants.get_illuminant_D65()
spectrum = color.calc_spectrum(reflectances, illuminant)
color_dict = color.calc_color(spectrum)
irgb_list.append(color_dict['irgb'])

# Plot those colors
print('Making color vs SiO2 thickness graph. Compare to (for example)')
print('http://www.htelabs.com/appnotes/sio2_color_chart_thermal_silicon_dioxide.htm')
plt.figure()
plt.plot([0, max_SiO2_thickness], [1, 1])
plt.xlim(0, max_SiO2_thickness)
plt.ylim(0, 1)
plt.xlabel('SiO2 thickness (nm)')
plt.yticks([])
plt.title('Air / SiO2 / Si color vs SiO2 thickness')
for i in range(len(SiO2_thickness_list)):
# One strip of each color, centered at x=SiO2_thickness_list[i]
if i == 0:
x0 = 0
else:
x0 = (SiO2_thickness_list[i] + SiO2_thickness_list[i-1]) / 2
if i == len(SiO2_thickness_list) - 1:
x1 = max_SiO2_thickness
else:
x1 = (SiO2_thickness_list[i] + SiO2_thickness_list[i+1]) / 2
y0 = 0
y1 = 1
poly_x = [x0, x1, x1, x0]
poly_y = [y0, y0, y1, y1]
color_string = colorpy.colormodels.irgb_string_from_irgb(irgb_list[i])
plt.fill(poly_x, poly_y, color_string, edgecolor=color_string)

[docs]def sample6():
"""
An example reflection plot with a surface plasmon resonance (SPR) dip.
Compare with http://doi.org/10.2320/matertrans.M2010003 ("Spectral and
Angular Responses of Surface Plasmon Resonance Based on the Kretschmann
Prism Configuration") Fig 6a
"""
# list of layer thicknesses in nm
d_list = [inf, 5, 30, inf]
# list of refractive indices
n_list = [1.517, 3.719+4.362j, 0.130+3.162j, 1]
# wavelength in nm
lam_vac = 633
# list of angles to plot
theta_list = linspace(30*degree, 60*degree, num=300)
# initialize lists of y-values to plot
Rp = []
for theta in theta_list:
Rp.append(coh_tmm('p', n_list, d_list, theta, lam_vac)['R'])
plt.figure()
plt.plot(theta_list/degree, Rp, 'blue')
plt.xlabel('theta (degree)')
plt.ylabel('Fraction reflected')
plt.xlim(30, 60)
plt.ylim(0, 1)
plt.title('Reflection of p-polarized light with Surface Plasmon Resonance\n'
'Compare with http://doi.org/10.2320/matertrans.M2010003 Fig 6a')
```