 The components of the electron's crystal momentum known from ARPES in this mapping geometry are thus

If high symmetry axes of the sample are known and need to be aligned, a correction by azimuth φ can be applied, either by rotating around z, formula_26 , or by rotating the map "I"("E", "k"x, "k"y) around origin in two-dimensional momentum planes.Theory of photoemission is that of direct optical transitions between the states formula_27 and formula_28 of an N-electron system.The light excitation is introduced as the magnetic vector potential formula_29 through the minimal substitution formula_30 in the kinetic part of the quantum-mechanical Hamiltonian for the electrons in the crystal.