Direct observation of second-harmonic generation from crystalline particles in Ge-doped SiO2 glass films

The authors report what is, to our best knowledge, the first observation of second-harmonic generation (SHG) directly from the crystalline particles in Ge-doped SiO2 (Ge:SiO2) glass films. Ge:SiO2 glass films with approximately 5 microm thickness were fabricated by chemical vapor-phase deposition. X-ray diffraction (XRD) peaks at around 2theta=22 degrees in thermally crystallized Ge:SiO2 films were observed, and obtained XRD patterns are exactly the same as those in ultraviolet-laser-poled Ge:SiO2 glasses. Using SHG microscopic technique with a Nd:YAG laser, it has been successfully found that SH emitting with 532 nm wavelength is observed directly from the crystalline particles induced in the crystallized films.