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 μm thickness were fabricated by chemical vapor-phase deposition. X-ray diffraction (XRD) peaks at around 2θ=22° 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.