GAVRILA, M. ., Maquet, A. ., & Véniard, V. . (1985). 2-PHOTON FREE-FREE TRANSITIONS IN A COULOMB POTENTIAL. PHYSICAL REVIEW A, 32, 2537-2540.
Maquet, A. ., GAVRILA, M. ., & Véniard, V. . (1985). Multiphoton transitions in the Coulomb continuous spectrum. Lecture Notes in Physics, 229, 275.