  Cavity-based quantum node is a competitive platform for distributed quantum
networks. Here, we characterize a high-finesse Fabry-Perot optical resonator
for coupling single or few atomic quantum registers. Our cavity consists of two
mirrors with different reflectivities: One has minimal optical loss, and the
other high transmission loss where more than 90% of the intracavity photons
would be emitted. Cavity finesse, birefringent effects, and mechanical
resonances are measured using the lasers at 780, 782, and 795 nm. In order to
obtain cavity geometric parameters, we drive the adjacent longitudinal or
transverse modes with two lasers simultaneously, and measure those frequencies
using a precision wavelength meter (WLM). A major novelty of this method is
that the parameters' uncertainties are solely determined by the resolution of
the WLM, eliminating all of the temporal environment fluctuations. Our scheme
makes it possible to quantify the atom-cavity coupling constant up to four
significant figures, the most precise and accurate estimation so far, which
would become a key ingredient for benchmarking a cavity-based quantum node.
Furthermore, the distortion of polarized photonic qubits would be minimized
owing to the small birefringent splitting, below 4.9% of the cavity linewidth.
Our system should operate in the intermediate atom-cavity coupling regime that
would allow us to implement various quantum network protocols.
