The influence of phosphate glass structure on results of thermal poling.

Two sodium phosphate glasses with different structure (meta- and orthophosphate ones) were thermally poled well below the glass transition temperatures. Glass with an orthophosphate structure (glass LA30) demonstrated a typical behavior of polarization current, that is, monotonic current decrease; however, in glass with a metaphosphate structure (glass LA10) the current first increased for 15-20 min and only then started monotonic decreasing. In spite of the similar sodium content, the current in LA10 glass exceeded the one in LA30 glass by about 10 times. This is explained by the capability of substituting intrinsic sodium ions by more mobile protons entering LA10 glass with a metaphosphate structure from the atmosphere. The other difference consists in the fact that the subanodic layer of LA10 glass after poling has many small cracks, while the subanodic layer of LA30 glass is crystallized. It should be emphasized that the crystallization of phosphate glasses under dc electric field below glass transition temperature is observed for the first time. In addition, after poling, no changes in the refractivity of both glasses were detected, but the generation of the second optical harmonic in LA30 glass was observed.

Poling of Glasses Using Resistive Barrier Discharge Plasma.

A technique for poling of glasses using a resistive barrier discharge plasma in the atmosphere in a gap of hundreds of microns is presented. Measurements of the polarization current, second harmonic generation, and IR spectra of poled soda-lime glass slides show that voltage sufficient to ignite plasma discharge provides efficient poling, whereas for lower voltages the poling effect is close to zero. We attributed this to the large number of hydrogen/hydronium ions generated from atmospheric water vapor by the plasma discharge in the gap, which penetrate into the glass. We also developed a simple model of poling according to Ohm's law, analyzed the temporal dependencies of the polarization current and, basing on the model, estimated mobilities of hydrogen/hydronium and sodium ions in the glass: µH = (2.4 ± 0.8) × 10-18 m2V-1s-1 and µNa = (4.8 ± 1.8) × 10-15 m2V-1s-1. The values obtained are very close to the known literature data.

2D-patterning of self-assembled silver nanoisland films.

The paper is dedicated to the recently developed by the authors technique of silver nanoisland growth, allowing self-arrangement of 2D-patterns of nanoislands. The technique employs silver out-diffusion from ion-exchanged glass in the course of annealing in hydrogen. To modify the silver ion distribution in the exchanged soda-lime glass we included the thermal poling of the ion-exchanged glass with a profiled electrode as an intermediate stage of the process. The resulting consequence consists of three steps: (i) during the ion exchange of the glass in the AgxNa1-xNO3 (x = 0.01-0.15) melt we enrich the subsurface layer of the glass with silver ions; (ii) under the thermal poling, the electric field displaces these ions deeper into the glass under the 2D profiled anodic electrode, the displacement is smaller under the hollows in the electrode where the intensity of the field is minimal; (iii) annealing in a reducing atmosphere of hydrogen results in silver out-diffusion only in the regions corresponding to the electrode hollows, as a result silver forms nanoislands following the shape of the electrode. Varying the electrode and mode of processing allows governing the nanoisland size distribution and self-arrangement of the isolated single nanoislands, pairs, triples or groups of several nanoislands-so-called plasmonic molecules.

Out-diffused silver island films for surface-enhanced Raman scattering protected with TiO2 films using atomic layer deposition.

We fabricated self-assembled silver nanoisland films using a recently developed technique based on out-diffusion of silver from an ion-exchanged glass substrate in reducing atmosphere. We demonstrate that the position of the surface plasmon resonance of the films depends on the conditions of the film growth. The resonance can be gradually shifted up to 100 nm towards longer wavelengths by using atomic layer deposition of titania, from 3 to 100 nm in thickness, upon the film. Examination of the nanoisland films in surface-enhanced Raman spectrometry showed that, in spite of a drop of the surface-enhanced Raman spectroscopy (SERS) signal after the titania spacer deposition, the Raman signal can be observed with spacers up to 7 nm in thickness. Denser nanoisland films show slower decay of the SERS signal with the increase in spacer thickness. PACS: 78.67.Sc (nanoaggregates; nanocomposites); 81.16.Dn (self-assembly); 74.25.nd (Raman and optical spectroscopy).

Ultrasmall microdisk and microring lasers based on InAs/InGaAs/GaAs quantum dots.

Ultrasmall microring and microdisk lasers with an asymmetric air/GaAs/Al0.98Ga0.02As waveguide and an active region based on InAs/InGaAs/GaAs quantum dots emitting around 1.3 µm were fabricated and studied. The diameter D of the microrings and microdisks was either 2 or 1.5 µm, and the inner diameter d of the microrings varied from 20% to 70% of the outer diameter D. The microring with D = 2 µm and d = 0.8 µm demonstrated a threshold pump power as low as 1.8 µW at room temperature. Lasing was observed up to 100°C owing to the use of quantum dots providing high confinement energy both for electrons and holes. Tuning spectral positions of the whispering gallery modes via changing the inner diameters of the microrings was demonstrated. PACS: 78.67.Hc; 42.55.Sa; 42.50.Pq; 78.55.Cr.

Plasmonic bandgap in random media.

We present a dispersion theory of the surface plasmon polaritons (SPP) in random metal-dielectric nanocomposite (MDN) consisting of bulk metal embedded with dielectric inclusions. We demonstrate that embedding of dielectric nanoparticles in metal results in the formation of the plasmonic bandgap due to strong coupling of the SPP at the metal-vacuum interface and surface plasmons localized at the surface of nanoinclusions. Our results show that MDN can replace metals in various plasmonic devices, which properties can be tuned in a wide spectral range. Being compatible with waveguides and other photonic structures, MDN offers high flexibility in the plasmonic system design.

Nanoscale patterning of metal nanoparticle distribution in glasses.

: We show that electric field imprinting technique allows for patterning of metal nanoparticles in the glass matrix at the subwavelength scale. The formation of glass-metal nanocomposite strips with a width down to 150 nm is demonstrated. The results of near-field microscopy of imprinted patterns are in good agreement with the performed numerical modeling. Atomic force microscopy reveals that imprinting also results in the formation of nanoscale surface profile with the height going down with the decrease of the strip width. The experiments prove the applicability of this technique for the fabrication of nanoscale plasmonic components.

Self-assembled silver nanoislands formed on glass surface via out-diffusion for multiple usages in SERS applications.

We demonstrate that silver nanoisland film self-assembled on the surface of silver-containing glass in the course of thermal processing in hydrogen is capable to detect 10-7 M concentration of rhodamine 6G in water using surface enhanced Raman spectroscopy (SERS) technique. The film can be multiply restored on the same glass substrate via annealing of the glass in hydrogen. We showed that the film can be self-assembled after as much as ten circles of the substrate cleaning followed by annealing. The proposed technique of the silver nanoisland film formation enables multiple usage of the same glass substrate in SERS experiments.

Holmium lasers passively Q-switched with PbS quantum-dot-doped glasses.

PbS quantum-dot-doped glasses are demonstrated as saturable absorber Q-switches for 2 microm holmium lasers. Q-switched pulses from Ho3+:Y3Sc2Al3O12 and Ho3+:Y3Al5O12 lasers of 50 and 70 ns in duration, respectively, have been obtained demonstrating up to 13% of energy conversion efficiency from free-running to Q-switched output.