1337 nm Emission of a Nd3+-Doped TZA Glass Random Laser.

Random lasers have been studied using many materials, but only a couple have used glass matrices. Here, we present a study of zinc tellurite and aluminum oxide doped with different percentages of neodymium oxide (4 wt.%, 8 wt.%, and 16 wt.%) and demonstrate for the first time random laser action at 1337 nm. Laser emission was verified and the laser pulse's rise time and input-output power slope were obtained. A cavity composed of the sample's pump surface and an effective mirror formed by a second, parallel layer at the gain-loss boundary was probably the main lasing mechanism of this random laser system. The reason for the absence of emission at 1064 nm is thought to be a measured temperature rise in the samples' active volume.

Random laser emission from neodymium doped alumina lead-germanate glass powder.

Random lasing is reported for the first time, to our knowledge, in neodymium doped alumina lead-germanate (GPA) glass powder. The samples were fabricated by a conventional melt-quenching technique at room temperature, and x-ray diffraction was used to confirm the amorphous structure of the glass. Powders with average grain size of about 2 µm were prepared by grinding the glass samples and using sedimentation in isopropyl alcohol to remove the coarsest particles. The sample was excited using an optical parametric oscillator tuned to 808 nm, in resonance with the neodymium ion (N d 3+) transition 4 I 9/2→{4 F 5/2,2 H 9/2}. Random laser (RL) emission at 1060 nm (N d 3+ transition: 4 F 3/2→4 I 11/2) was observed for an energy fluence excitation threshold (E F E r m t h ) of about 0.3m J/m m 2. Above the E F E t h , a short RL pulse in the nanosecond range is observed, corroborating the lasing process. Contrary to what one might suppose, the use of large quantities of neodymium oxide (10% wt. of N d 2 O 3) in the GPA glass, which leads to luminescence concentration quenching (LCQ), is not a disadvantage, once stimulated emissions (RL emission) occur faster than the nonradiative energy-transfer time among N d 3+ ions responsible for the LCQ.

Optical limiting in multilayer graphene films on a cobalt buffer-layer produced by the sputtering technique.

Multilayer graphene (MLG) thin films were produced by a sputtering technique on a cobalt buffer-layer prepared at 500°C and thermal annealed after the deposition. The transformation of amorphous carbon (C) to graphene occurs by diffusion of C atoms through the catalyst metal; then the C atoms dissolved in the metal are nucleated as graphene. The thicknesses of cobalt and MLG thin films were 55 and 54 nm, respectively, obtained by atomic force microscopy (AFM). Raman spectroscopy showed that the ratio between the Raman bands 2D and G (I 2D /I G ) was 0.4 for the graphene thin film that was annealed at 750°C for 25 min, indicating that the films obtained are MLG. The Raman results were corroborated by transmission electron microscopy analysis. AFM was used to determine the Co and C film thickness and roughness. Transmittance measurements at 980 nm as a function of input power from a continuous-wave diode laser showed that the obtained MLG films present large nonlinear absorption and can be used as optical limiters.

Effect of Silver Nanoparticles on the Optical Properties of Double Line Waveguides Written by fs Laser in Nd3+-Doped GeO2-PbO Glasses.

Nd3+-doped GeO2-PbO glass with silver (Ag) nanoparticles (NPs) are produced with double line waveguides through fs laser processing for photonic applications. A Ti:sapphire fs laser at 800 nm was used to write the waveguides directly into the glass 0.7 mm beneath the surface. This platform is based on pairs of parallel lines with spacing of 10 µm, each pair being formed by two identical written lines but in two different configurations of 4 or 8 separately processed lines, which are coincident. The results of optical microscopy, absorbance measurements, refractive index change, beam quality factor (at 632 and 1064 nm), photoluminescence, propagation losses, and relative gain at 1064 nm are presented. The structural changes in the glass due to the presence of Ag NPs were investigated by Raman spectroscopy. At 632 and 1064 nm, x,y-symmetrical guiding was observed, and for both kinds of overlapping pulses, a refractive index alteration of 10-3 was found in both directions. Photoluminescence growth of ~47% at 1064 nm was observed due to the plasmonic effect of Ag NPs. In dual waveguides containing Ag NPs, the relative gain obtained increased by 40% and 30% for four and eight overlapping lines, respectively, at 600 mW of 808 nm pump power, when compared to waveguides without those metallic NPs. We highlight the resultant positive internal gains of 5.11 and 7.12 dB/cm that showed a growth of ~40% and ~30%, respectively, with respect to the samples without Ag NPs. The increase in photoluminescence and relative gain were related to the local field growth produced by Ag NPs. The present results show that the addition of Ag NPs impacts positively on the optical performance at 1064 nm of double line waveguides processed by fs laser writing in Nd3+-doped GeO2-PbO glass, opening news perspectives for photonics.

Random lasing and replica symmetry breaking in GeO2-PbO-MgO glass-ceramics doped with neodymium.

We investigated the random lasing process and Replica Symmetry Breaking (RSB) phenomenon in neodymium ions (Nd3+) doped lead-germanate glass-ceramics (GCs) containing MgO. Glass samples were fabricated by conventional melt-quenching technique and the GCs were obtained by carefully devitrifying the parent glasses at 830 °C for different time intervals. The partial crystallization of the parent glasses was verified by X-ray diffraction. Photoluminescence (PL) enhancement of [Formula: see text] 500% relative to the parent glasses was observed for samples with a higher crystallinity degree (annealed during 5 h). Powders with grains having average size of 2 µm were prepared by griding the GCs samples. The Random Laser (RL) was excited at 808 nm, in resonance with the Nd3+ transition 4I9/2 → {4F5/2, 2H9/2}, and emitted at 1068 nm (transition 4F3/2 → 4I11/2). The RL performance was clearly enhanced for the sample with the highest crystallinity degree whose energy fluence excitation threshold (EFEth) was 0.25 mJ/mm2. The enhanced performance is attributed to the residence-time growth of photons inside the sample and the higher quantum efficiency of Nd3+ incorporated within the microcrystals, where radiative losses are reduced. Moreover, the phenomenon of Replica Symmetry Breaking (RSB), characteristic of a photonic-phase-transition, was detected by measuring the intensity fluctuations of the RL emission. The Parisi overlap parameter was determined for all samples, for excitation below and above the EFEth. This is the first time, for the best of the authors knowledge, that RL emission and RSB are reported for a glass-ceramic system.

Process Oxygen Flow Influence on the Structural Properties of Thin Films Obtained by Co-Sputtering of (TeO2)x-ZnO and Au onto Si Substrates.

In this study, we investigated the structural properties of TeO2-ZnO (TZ) and TeO2-ZnO-Au (TZA) thin films sputtered under different oxygen concentrations and either annealed or not annealed at 325 °C in air for 10 or 20 h. The lattice changes of the tellurium oxide were shown to be inherent in the polymorph properties of the α and ß phases. The ß phase was formed for null oxygen flow and the α phase was formed for different oxygen flows (0.5-7.0 sccm) during TZ and TZA sputtering. Au was encountered in its single phase or as AuTe2. The annealing had very little influence on the α and ß phases for both TZ and TZA. It is worth noting that SiO2 and orthotellurate anions are both formed for not-null oxygen flow. An electrochemical mechanism was proposed to explain the SiO2 growth at the TZ/Si or TZA/Si interface, taking the orthotellurate anion as oxidizing agent into account.

Femtosecond third-order nonlinear spectra of lead-germanium oxide glasses containing silver nanoparticles.

This work reports on the spectral dependence of both nonlinear refraction and absorption in lead-germanium oxide glasses (PbO-GeO2) containing silver nanoparticles. We have found that this material is suitable for all-optical switching at telecom wavelengths but at the visible range it behaves either as a saturable absorber or as an optical limiter.