Abstract—approaches for calculating the amplitudes of nonlinear photoprocesses in the framework of perturbation theory. The convergence of the method is studied based on the example of atomic hydrogen and hydrogenlike ions. The method is used to calculate the angular distributions of photoelectrons for the first time.
$^1$Department of Physics, Moscow State University, Moscow, 119991 Russia
$^2$Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119191 Russia