Laser-induced cavities with a controllable shape in nanoporous glass.

The formation of birefringent structures inside nanoporous glass by femtosecond laser pulses was investigated. The laser-modified region is shown to be a cavity whose shape depends on the number of pulses. The shape of the void cross section varied from circle to ellipse when increasing the number of pulses from one to three. A layer of non-porous dense glass was revealed around the cavity. The cross section of this layer is nearly circular, regardless of the cavity shape and number of pulses in the investigated range. The mechanism of elongated cavity formation based on aniostropic light scattering on the spherical cavity is proposed.

Ultrafast laser-induced nanogratings in sodium germanate glasses.

We report ultrafast laser inscription of nanogratings possessing form birefringence in binary sodium germanate glasses in a wide range of Na2O content from 3 to 22 mol.%. A minimal number of laser pulses required to induce noticeable form birefringence is shown to grow exponentially with Na2O content in glass. Atomic force microscopy showed similarity of their periodical structure and period value to those in the nanogratings formed in fused silica. A sharp pulse duration threshold below which laser pulses do not induce nanogratings in the studied glasses has been revealed. Formation of a nanograting in 22Na2O·78GeO2 at the studied conditions is accompanied by crystallization of a surrounding submicron layer and partial crystallization inside the nanograting with precipitation of Na2Ge4O9 crystals.

Direct femtosecond laser-induced formation of CdS quantum dots inside silicate glass.

We report the one-step precipitation of CdS quantum dots in the volume of CdS-doped silicate glass under the focused femtosecond laser beam without additional heat treatment of glass. Femtosecond direct laser writing leads to the annular distribution of the precipitated CdS quantum dots in laser-written domain optical properties of which could be tuned by laser beam parameters. Increasing the laser pulse number to 103 significantly enhances luminescence intensity in the domains, while further increasing up to 106 pulses leads to luminescence quenching. A possible scenario for the formation and distribution of quantum dots is proposed.

3-bit writing of information in nanoporous glass by a single sub-microsecond burst of femtosecond pulses.

We have found that a single sub-microsecond burst of femtosecond laser pulses produces a sub-micrometer cavity possessing the homogeneous birefringence with slow-axis orientation perpendicular to polarization of the laser beam in high-silicate nanoporous glass. Retardance and the root mean square of slow-axis orientation are investigated in dependence on the energy and the number of pulses in the burst. A burst of just three pulses with 98 ns inter-pulse intervals has been shown to induce homogeneous birefringence, and a burst of four pulses has provided birefringence with retardance of 35 nm, which is sufficient for reliable readout of the information recorded with multilevel encoding in slow-axis orientation. A text file has been recorded and read out in an array of birefringent cavities, each carrying 3 bits of information. The sub-microsecond burst of femtosecond pulses paves the way for a multiple increase of the rate of digital information recording with multilevel encoding in glass.

Broadband infrared light-emitting patterns in optical glass by laser-induced nanostructuring of NiO-doped alkali-gallium germanosilicates.

In this Letter, we show functionalization of NiO-doped 7.5Li(2)O·2.5Na(2)O·20Ga(2)O(3)·35SiO(2)·35GeO(2) glass by space-selective nanocrystallization via exposure to the focused beam of a pulsed copper vapor laser (510.6 and 578.2 nm) at temperature close to the glass transition point (570°C). Irradiated areas drastically change their color, caused by electronic transitions of Ni(2+) dopant ions, without any alteration of the optical quality. Importantly, irradiated regions acquire broadband infrared luminescence (centered at about 1400 nm and possessing 400 nm effective bandwidth) typical of Ni(2+) ions in crystalline environment, and by positive change of refractive index (more than 10(-3)). Spectroscopic and diffractometric data of the irradiated regions indeed resemble those previously observed in thermally nanocrystallized glass, with Ni(2+) ions embedded in γ-Ga(2)O(3) nanocrystals. The results demonstrate the possibility of laser writing nanocrystallized multifunction patterns in germanosilicate glasses for the fabrication of active integrated devices.