  The figure of merit (FoM) of Ti:Sapphire (Ti:Sa) crystals is a generally used
means to evaluate the quality of the crystals. Despite the importance of Ti:Sa,
the question of FoM measurement precision stayed out of focus, while the
commercially available spectrometers provide unsatisfactory 3-sigma precision
reaching 60 %. In this paper, we present a setup for a single-pass
high-precision transmission measurement for three different wavelengths (532
nm, 780 nm, and 1560 nm) based on Nd:YAG and Er:YAG lasers. A synchronous
detection via a double integrated sphere enabled us to achieve the transmission
uncertainty of 0,01-0,03%. With the presented setup, we show that it is
possible to determine the FoM values with 3-sigma precision of 7,5 %. Owing to
the high FoM precision, we were able to trace spatial inhomogeneities of an
unannealed Ti:Sa crystal produced by a commercial manufacturer Crytur. Our
measurements demonstrate that the FoM values can be significantly affected by
the crystal inhomogeneities and angular mismatch between the c-axis of the
Ti:Sa and polarization orientation.
