Laser-induced micro-fabrication has many advantages such as maskless, single-step and very fast processing compared with current techniques such as photolithography and reactive ion etching. Laser-induced crystallization is now a big challenge in glass materials. A new technique for the writing of crystal dots and lines in glass, called "samarium (rare-earth) atom heat processing", has been developed, and the writing of several crystal lines such as b-BaB2O4 (b-BBO), SmxBi1-xBO3, Sm2(MoO4)3, and KSm(PO3)4 showing second harmonic generations and ferroelectricities has been succeeded. It has been also demonstrated that two-dimensional crystal curved lines with bending angles of 0~90o or with sine-curve shapes can be written using the samarium atom heat processing. The features of this new technique and the quality of crystal lines have been clarified.
Challenges for laser-induced structure ordering from nano-particles to single-crystal patterning in glasses are described. Transparent crystallization in glass must be the best material solution to obtain novel functional glasses with a permanent second-order optical nonlinearity. We focus on the new functions created by structure ordering in glass by means of laser micro-fabrication for space-selected crystallization. Two topics in our recent experimental results of laser-induced structure ordering in glass will be presented as follows: (1) UV-laser induced structure ordering of nano-particles in tellurite-based glasses and possible photonic integrated circuits with innovative minute scale. (2) Single crystalline patterning by atom heat laser processing in Sm-doped glasses for optical waveguides with second-order nonlinearity.
We propose and demonstrate gratings and two-dimensional (2D) photonic structure of nanometer-scale crystals/particles in glass surface created by one of the most simple way every reported. Grating structures consisting of nanocrystals have been fabricated on surface of tellurite-based glasses, with a composition of 15K2O-15Nb2O5-70TeO2 (mol%), using photoinduced nano-crystallization. A conventional phase mask technique was performed for the grating fabrication with a XeCl excimer laser operating at 308 nm. Periodic structure with 400 nm pitch constructed by lines of regularly ordered nanoparticles having a diameter up to about 100 nm was confirmed by atomic force microscopy and scanning electron microscopy. It is strongly suggest from measurement of X-ray diffraction that the photoinduced nanoparticles have a crystalline phase, and also suggested from measurement of optical frequency doubling that the periodic nanoparticle structure exhibits second harmonic generation (SHG) with an unique polarization dependence of SHG based on nano-structures of dielectric polarization. In addition, such a simple method of phase mask usage was applied to formation of 2D array, and the 2D structures of nano-particles/holes were successfully obtained by laser irradiations.