TODO : add Fun Fact #1 : The sun would not be visible if the 4.2 µm CO2 lineshape was truely lorentzian

[erwanp]

Add a notebook based on this (working) Python example :

"""

Fun Facts About Spectroscopy
----------------------------

# The sun would not be visible if the 4.2 µm CO2 lineshape was truely lorentzian
"""


from radis import calc_spectrum
import matplotlib.pyplot as plt
import astropy.units as u

s = calc_spectrum(wavelength_min=0.3*u.um, wavelength_max=6*u.um,
                  molecule='CO2',
                  isotope='1,2,3',
                  pressure=1.01325,   # bar
                  truncation=None, 
                  Tgas=300,           # K
                  mole_fraction=400e-6,
                  cutoff=0,
                  databank='hitran',  # or use 'hitemp'
                  broadening_method="fft"
                  )

# note : the calculation is quite long (~190s on my laptop) because the FFT
# method used is not optimized for very large ranges

#%% Plot
s.plot('abscoeff', wunit='nm', yscale='log')
plt.axvspan(300, 700, alpha=0.3) # visible spectrum

# we get an absorption coefficient of about ~0.5 cm-1 in the visible range

# %% 
# which means that the sky would be >99% more opaque for a layer of only ~ 10 cm 
# (exp(-5) = 0.006 )

s.rescale_path_length(10).plot('transmittance_noslit', wunit='nm')
plt.axvspan(300, 700, alpha=0.3) # visible spectrum
plt.ylim((0, 1.1))
# plt.ylim((0, 1.1))