Probing the spectral densities over the full three-dimensional momentum space

Electron momentum spectroscopy is often used to determine the spectral function of materials. It relies on the determination of the scattering angle of electrons with extremely high precision. In practice, it is important to calibrate these angles, and hence the momentum scales. Here we describe a method to do so and show how minor misalignments affect the measured momentum densities of Li₂O. Using the same procedure we further calibrated the momentum scale by measuring the spectral momentum density along a Brillouin zone boundary of a Si single crystal.