Karpierz, Miroslaw A., and George I. Stegeman. “Nonlinear Optics: A Vibrant Field”. Photonics Letters of Poland 1, no. 4 (January 4, 2010): pp. 145–147. Accessed July 22, 2024. http://photonics.pl/PLP/index.php/letters/article/view/1-49.