One of the most powerful technique to study electronic structure is the state-of-the-art Angle Resolved Photoemission Spectroscopy (ARPES). It has been proved to be particularly effective for measuring the electronic structure of condensed matter in momentum space since it allows direct detection of the single particle spectral function A(k,w) which contains lots of important information about electronic states including Fermi surfaces, energy band structure, Fermi velocity, energy gap, effective mass, carrier density, etc.