The 3 csv files are the data for the plots with the corresponding figure numbers. 
The header line(s) of each csv file contain the units of each axis.

These are:

figure2.csv - Faraday filter profile as a function of laser detuning. 
Columns are laser frequency detuning and transmitted intensity. 
The theory curve for this plot can be reproduced by using ElecSus [referenced within the paper]
with the parameters given in the caption to the figure.

figure3.csv - Short-term laser linewidth data
Direct, unprocessed output from spectrum analyser. 
The fits can be reproduced by fitting standard Lorentzian and Gaussian functions to the data

figure4.csv - Long-term frequency stability data
This is the raw time/beat-note-frequency data for figure 4, which can be processed using the 
overalapping Allan deviation (we used the AllanTools package [https://pypi.python.org/pypi/AllanTools])
to reproduce the purple curve in the figure