1. V. A. Fock, Electromagnetic diffraction and propagation problems (Pergamon Press, 1965).
2. V. M. Babich, V. S. Buldyrev. Asymptotic Methods in Short-Wavelength Diffraction Theory (Alpha Science, Oxford, 2009).
3. A. E. Siegman, Lasers (University Science Book, 1986).
4. A. P. Kiselev, Opt. Spectr., 102 (4), 603 (2007). https://doi.org/10.1134/S0030400X07040200
5. W. Miller, Jr., Symmetry and Separation of Variables (Addison-Wesley, London-Amsterdam, 1977).