Post Waveguide-like structures written in transparent polycrystalline ceramics with an ultra-low fluence femtosecond laser G.R. Castillo-Vega, E.H. Penilla, S. Camacho-López, G. Aguilar and J.E. Garay, "Waveguide-like structures written in transparent polycrystalline ceramics with an ultra-low fluence femtosecond laser," Optical Materials Express 2, 1416-1424 (2012).