1. Code 6362, Naval Research Laboratory, Washington, DC 20375, USA
2. Directed Energy Directorate, Air Force Research Laboratory, Albuquerque, New Mexico 87117, USA
3. Departments of Mathematics and Physics, Rutgers University, Piscataway, New Jersey 08854, USA
4. School of Computing and Engineering, University of Huddersfield, Huddersfield, United Kingdom