I. V. Blonskyi, V. M. Kadan, O. Y. Shpotyuk, P. I. Korenyuk, V. M. Puzikov, and L. O. Gryn’, “Filamentation in the Intersection Region of Two Femtosecond Laser Beams in Sapphire”, Ukr. J. Phys., vol. 59, no. 3, p. 344, Oct. 2018.