Ślęczka, Marcin, and Adam Bechler. “Atom Ionization by Strong Laser Pulses - Gauge Invariant Description”. Photonics Letters of Poland 5, no. 4 (December 31, 2013): pp. 155–57. Accessed April 19, 2024. https://www.photonics.pl/PLP/index.php/letters/article/view/5-55.