To realize the detection of electronic spin the most popular detector is the Mott spin detector.
Because of spin orbital coupling, the distribution of scattering electrons by heavy nucleus is anisotropic in different direction which is called Mott scattering, and the design of Mott spin detector is based on such an effect.

The specular feature of Mott scattering is that the asymmetrical scattering attributes to the electrons with polarization perpendicular to the scattering cross section.
The electronic polarization could be detected by analyzing the asymmetrical scattering intensity, and this kind of spin detecting method has been used in the Mott detector

The Mott scattering happens when electrons eject into the surface of a heavy metal, and the distribution of scattering electrons is different for electrons with different spins.

By comparing the counts of two electron counters, the polarization perpendicular to the ejecting election could be calculated.

The cross-section of Mott scattering is rather low, between 2*10^(-5) and 1.6*10^(-4) --> low scattering Efficiency. The counts of Mott spin detectors are usually only 1/10000 or 1/100000 of regular ARPES (Angle-resolved photoemission spectroscopy). 

To get reasonable counts, reduce the energy resolution (100 meV) and integrate the spectra over a wide angle (angel integrated photoemission spectroscopy).
Another way is inceasing the flux of incident photons, but that's impossible for synchroton light source and gas discharge lamp (increasing photon flux will broaden the bandwith of photons fpr synchrotron light source and the photon flux of gas discharge lamp is not tunable).