“Stress-induced waveguides in Nd:YAG by simultaneous double-beam irradiation with femtosecond pulses” G. R. Castillo, C. Romero, G. Lifante, D. Jaque, F. Chen, O. Varela, E. García, C. Méndez, S. Camacho-Lopez, and J. R. Vázquez de Aldana. Optical Materials 51, 84-88 (2016). http://dx.doi.org/10.1016/j.optmat.2015.11.025