  We present a careful calibration of the exciton fraction of polaritons in
high-$Q$ ($\sim 300,000$), long-lifetime ($\sim 300$ ps), GaAs/AlGaAs
microcavities.This is a crucial parameter for many-body theories which include
the polariton-polariton interactions.It is much harder to establish this number
in high-$Q$ structures compared to low-$Q$ structures, because the upper
polariton is nearly invisible in high-$Q$ cavities.We present a combination of
photoluminescence, photoluminescence excitation, and reflectivity measurements
to highly constrain the fit model, and compare the results of this model to the
results from low-$Q$ structures.We present a fitted curve of exciton fraction
as a function of the lower polariton energy for multiple samples which have
been used in prior experiments.
