def fig4():
""" n=3 or n=1 (air) to n=1.5 (Erbium deposition) semi-infinite half spaces.
Plot the average total spontaneous emission rate of dipoles as a function of
distance from the interface.
"""
# Vacuum wavelength
lam_vac = 1550
# Plotting units
units = lam_vac / (2 * pi)
# Create plot
f, ax = plt.subplots(figsize=(15, 7))
for n in [1, 3]:
print('Evaluating n={:g}'.format(n))
# Create structure
st = LifetimeTmm()
st.set_vacuum_wavelength(lam_vac)
st.add_layer(4 * units, n)
st.add_layer(4 * units, 1.5)
st.info()
# Calculate spontaneous emission over whole structure
result = st.calc_spe_structure_leaky()
z = result['z']
# Shift so centre of structure at z=0
z -= st.get_structure_thickness() / 2
spe = result['spe']['total']
# Plot spontaneous emission rates
ax.plot(z/units, spe, label=('n='+str(n)), lw=2)
ax.axhline(y=n, xmin=0, xmax=0.4, ls='dotted', color='k', lw=2)
# Plot internal layer boundaries
for z in st.get_layer_boundaries()[:-1]:
# Shift so centre of structure at z=0
z -= st.get_structure_thickness() / 2
ax.axvline(z/units, color='k', lw=2)
ax.axhline(1.5, ls='--', color='k', lw=2)
ax.set_title('Spontaneous emission rate at boundary for semi-infinite media. RHS n=1.5.')
ax.set_ylabel('$\Gamma / \Gamma_0$')
ax.set_xlabel('Position z ($\lambda$/2$\pi$)')
plt.legend()
plt.tight_layout()
if SAVE:
plt.savefig('../Images/spe_vs_n.png', dpi=300)
plt.show()
