1. An abstract representation of the scalar wave equation of optics, Part I;Kragl;ntz Archiv,1989
2. An abstract representation of the scalar wave equation of optics. Part 2;Kragl;ntz Archiv,1989
3. Operator methods in physical optics;Stolen;J. Opt. Soc. Am.,1981
4. Unitary operators in the homogeneous wave field;Montgomery;Optics letters,1981
5. Generalized mode propagation in first-order optical systems with loss or gain;Nazarathy;J. Opt. Soc. Am.,1982