Allows to synthesize complex-valued absorption spectra (i.e., intensity and phase) from the hitran database for different pressures/temperatures accounting for pressure and Doppler broadening, using HAPI. List of supported molecules: https://hitran.org/lbl/.
Uses JAX for acceleration if it is installed. Keep in mind that if you use a GPU, single precision is the default. Switching to double precision is recommended (import jax; jax.config.update("jax_enable_x64", True) at the beginning of your script, or set the environement variable JAX_ENABLE_X64=True).
In case you are using Windows: Previous to executing the commands below, install Anaconda, open Anaconda prompt and run conda install git. Then execute the commands below also from Anaconda prompt.
Use pip to install this package:
pip uninstall hitran-api
pip install git+https://gitlab.com/leberwurscht/hitran_syn.git
pip install joblibThe first line will uninstall the official version of hitran-api (HAPI), because hitran_syn needs a custom version of it (see hitranonline/hapi#49). The second line will install hitran_syn with its dependencies (also the custom version of HAPI). The third line will install joblib, which is needed to run the example below.
import numpy as np
import matplotlib.pyplot as plt
import joblib # pip install joblib
memory = joblib.Memory("cache")
import hitran_syn # pip install git+https://gitlab.com/leberwurscht/hitran_syn.git
### list available molecules from HITRAN
print("available molecules:")
for i in hitran_syn.available_molecules:
print("\t", i)
print()
### compute propagation coefficient
@memory.cache # takes some time (~1 min on my computer), so cache the result with joblib.Memory
def get_data(nu_min, nu_max):
nu = np.linspace(nu_min,nu_max,25000)
pressure = 101325 # 1 atm in Torr
temperature = 273.15+20 # 20°C in Kelvin
fraction = 100e-6 # 100 ppm
molecule_name = "(12C)H3(16O)H" # ... of methanol
gamma = hitran_syn.propagation_coefficient(molecule_name,nu,total_pressure=pressure,partial_pressure=fraction*pressure,temperature=temperature)
return nu, gamma
### plot
nu, gamma = get_data(20e12, 40e12)
sample_length = 1 # in meters
transmission_coefficient = np.exp(-gamma*sample_length)
fig = plt.figure(constrained_layout=True)
gs = fig.add_gridspec(2,1)
ax = fig.add_subplot(gs[0,0])
ax.plot(nu/1e12, abs(transmission_coefficient)**2 / 1e-2)
ax.set_xlabel("optical frequency (THz)")
ax.set_ylabel(r"PSD$_\mathrm{out}$/PSD$_\mathrm{in}$ (%)")
ax = fig.add_subplot(gs[1,0])
ax.plot(nu/1e12, np.angle(transmission_coefficient))
ax.set_xlabel("optical frequency (THz)")
ax.set_ylabel("spectral phase change (rad)")
fig.suptitle("transmission through {} meters of 100 ppm methanol at 1 atm, 20°C".format(sample_length))
plt.savefig("output.png")
plt.show()
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