Efficient neodymium-doped glass-ceramic fiber laser and amplifier

We report an efficient glass-ceramic fiber laser and show that its slope efficiency (~30%) is not compromised by the presence of Nd-doped fluoride crystals embedded within the core of the single-mode optical fiber. In contrast, the spectroscopy (fluorescence and gain spectrum) of the Nd(3+) ions is dramatically changed by the ceramming process, an indication of strong partitioning of the rare-earth ions into the CdF(2):PbF(2):YF(3) crystal environment. The enormous potential for a new range of optical devices based on transparent glass-ceramic materials is highlighted.     

Ion-exchanged tapered-waveguide laser in neodymium-doped BK7 glass

We report what is to our knowledge the first operation of a planar dielectric tapered-waveguide laser. The waveguide laser is fabricated by potassium-ion exchange in Nd(3+) -doped BK7 glass and consists of a single-mode channel waveguide of a few micrometers' width followed by a linear taper up to a broad region with a width of ~180microm . A slope efficiency of 42% is found both in the tapers and in standard channel waveguides fabricated upon the same substrate, indicating that the tapers and the channels have similar internal losses; hence the low-loss nature of the tapered beam expansion. The output from either end of the tapered structure is found to be nearly diffraction limited.     

Multinuclear NMR studies on the sol-gel preparation of sodium aluminophosphate glasses

Sodium aluminophosphate gels and glasses in the system NaPO₃–Al₂O₃ with P/Al ratios ranging from 9:1 to 1:1 have been synthesized by a novel sol–gel route based on the reaction of aluminum lactate with sodium polyphosphate in aqueous solution. The route from the solution to the gel and the final glass was monitored in situ by liquid and solid state NMR techniques, characterizing the influence of composition and pH on the hydrolysis, polymerization, and vitrification processes. The site distribution in the xerogels is strongly influenced by the gel-processing temperature. At temperatures near 150°C ligation with lactate groups can be nearly suppressed, resulting in maximum Al/P connectivity in the gel. Annealing the gels at temperatures near 400°C produces significant structural rearrangements, resulting in a glassy network that has close structural similarity to the glasses derived from the usual melt-cooling procedure at 1100–1450°C. This has been confirmed by extensive ²⁷Al, ³¹P and ²³Na MAS NMR as well as ²⁷Al{³¹P} and ²⁷Al {¹H} double resonance experiments. Compared to melt-cooling, the sol–gel process permits a significant extension of the glass-forming region towards higher alumina contents.     

Watt-level output rectangular-core neodymium-doped silicate glass fiber laser

We produce a maximum 1.45 W laser output at 1064 nm using a neodymium-doped silicate glass fiber that has a rectangular core with dimensions of ~6.3 μm× 31.5 μm. The measured divergence angles of the output laser in two dimensions are 3.22° and 1.76°, respectively. The output power is stable and limited only by the available pump power.     

An advanced NMR protocol for the structural characterization of aluminophosphate glasses

In this work a combination of complementary advanced solid-state nuclear magnetic resonance (NMR) strategies is employed to analyse the network organization in aluminophosphate glasses to an unprecedented level of detailed insight. The combined results from MAS, MQMAS and (31)P-{(27)Al}-CP-heteronuclear correlation spectroscopy (HETCOR) NMR experiments allow for a detailed speciation of the different phosphate and aluminate species present in the glass. The interconnection of these local building units to an extended three-dimensional network is explored employing heteronuclear dipolar and scalar NMR approaches to quantify P-O-Al connectivity by (31)P{(27)Al}-heteronuclear multiple quantum coherence (HMQC), -rotational echo adiabatic passage double resonance (REAPDOR) and -HETCOR NMR as well as (27)Al{(31)P}-rotational echo double resonance (REDOR) NMR experiments, complemented by (31)P-2D-J-RESolved MAS NMR experiments to probe P-O-P connectivity utilizing the through bond scalar J-coupling. The combination of the results from the various NMR approaches enables us to not only quantify the phosphate units present in the glass but also to identify their respective structural environments within the three-dimensional network on a medium length scale employing a modified Q notation, Q(n)(m),(AlO)(x), where n denotes the number of connected tetrahedral phosphate, m gives the number of aluminate species connected to a central phosphate unit and x specifies the nature of the bonded aluminate species (i.e. 4, 5 or 6 coordinate aluminium).     

Nonstoichiometric laser materials: Designer wavelengths in neodymium-doped garnets

The tunable nature of lasers provides for a wide range of applications. Most applications rely on finding available laser wavelengths to meet the needs of the research. This article presents the concept of compositional tuning, whereby the laser wavelength is designed by exploiting nonstoichiometry. For research where precise wavelengths are required, such as remote sensing, this is highly advantageous. A theoretical basis for the concept is presented and experimental results in spectroscopic measurements support the theoretical basis. Laser operation nicely demonstrates the validity of the concept of designer lasers.     

Spectroscopic analysis and laser modeling of neodymium-doped potassium lead chloride

We present a discussion of the low-phonon energy host material potassium lead chloride, KPb₂Cl₅, doped with neodymium. Crystal growth, spectroscopic measurements, and an analysis of the magnetic and electric dipole transitions based on the Judd-Ofelt model are presented. Concentration quenching of the fluorescence is also examined. Based on the spectroscopic data and the known resonances in energy spacing of the first three excited states in neodymium, we suggest the possibility of a 3-for-1 cross-relaxation process. This process may efficiently populate the first excited state, ⁴I_11/2, which we show to be metastable with lifetime on the order of a few milliseconds. Population inversion of this level should be possible enabling a laser based on the 5.5-μm, ⁴I_11/2 to ⁴I_9/2 transition.     

Single-mode direct-ultraviolet-written channel waveguide laser in neodymium-doped silica on silicon

A waveguide laser with a neodymium-doped silica core is fabricated on a silicon substrate by a combination of flame hydrolysis deposition, solution doping, and direct UV writing. The neodymium-ion concentration is estimated to be approximately 8000 parts in 10(5). The propagation loss around 1.05 microns is < 0.8 dB/cm. Lasing in the range 1048-1056 nm and 1356 +/- 1 nm is observed. A slope efficiency of 33% for a high-reflectivity output coupler and a threshold of 4 mW of absorbed power for a 25% output coupler are measured for the 4F3/2-->4I11/2 transition.     

On the relation between thermally stimulated depolarization and thermoelectricity in irradiated aluminophosphate glasses

Several reasons are given to assume both the maximum of thermally stimulated depolarization near 100 °C and the thermovoltaic effect in aluminophosphate glasses to be associated with the movement of protons. The assumption, that the glasses are hydrolyzed, is supported by this finding.     

Microstructured silicon created with a nanosecond neodymium-doped yttrium aluminum garnet laser

We produce microstructured silicon using frequency doubled, nanosecond Nd:YAG pulses in SF₆ gas. The micro-penitentes formed are up to 20 μm tall with a sulfur concentration of 0.5% near the surface. The infrared absorption is increased to near unity and extends well below the original bandgap far into the infrared. These data are similar to results reported by others using more complicated and less economical femtosecond titanium sapphire and picosecond and nanosecond excimer lasers.     

Properties of yttrium-iron-metalloid glasses

We report the results of measurements on metallic glasses of the form Y₆₆(Fe_1–x M _x )₃₄. For M = B we find that there is an extended range of glass formation (0x0.40) and that properties such as atomic density, electrical resistivity, microhardness, and thermal stability are functions ofx. For M = C, Si, or Ge we find a restricted range of glass formation (0 x0.10) and no significant changes in the properties of the glasses. Using Fe⁵⁷ Mössbauer effect spectroscopy we find that the M = B case is again unique in that the structure of the glass is sensitive to B content. We relate the differences in glass formation for the M = B and M = C, Si, Ge glasses to the existence of Y rich compounds in the C, Si, and Ge cases and the lack of such compounds in the M = B case.     

A moisture-resistant antireflective coating by sol-gel process for neodymium-doped phosphate laser glass

Using methyl triethoxysilicane as precursor, a moisture-resistant coating for neodymium-doped laser glass was developed by the sol-gel process. Colloidal silica was added in coating solution as modifier. The refractive index of this coating varied from 1.31 to 1.42. A porous antireflective (AR) silica coating with the index of 1.27 was coated on the moisture-resistant coating surface. The two-layer coating possessed transmission up to 99.1% at wavelength of 966 nm, surface root-mean-square (RMS) roughness of 1.245 nm, and roughness of average (RA) of 0.961 nm. In the case of laser of 1053-nm laser wavelength and 1-ns pulse duration, the damage threshold of the two-layer coatings was more than 15 J/cm2.     

Q-switched neodymium-doped Y3Al5O12-based silica fiber laser

We present pulsed laser operation in a Nd-doped, Y3Al5O12-based silica fiber. The fiber was fabricated using the rod-in-tube technique with a Nd:YAG crystal rod as the core material and a silica tube for the cladding material. A spectroscopy study revealed that the core region had become amorphous in the process of fiber drawing. Q-switched pulsed laser operation was realized at a wavelength of 1058 nm when the fiber was cladding pumped at a wavelength of 808 nm. The laser delivered 38 μJ of energy in 65 ns pulses. The extracted energy was limited due to the multimodal operation of the fiber. Laser slope efficiency in continuous wave operation reached 52%. The spectroscopic properties of the fabricated fiber are discussed and compared to a Nd:YAG crystal and a Nd:Al-doped silica fiber.     

A moisture-resistant antireflective coating by sol-gel process for neodymium-doped phosphate laser glass

Using methyl triethoxysilicane as precursor, a moisture-resistant coating for neodymium-doped laser glass was developed by the sol-gel process. Colloidal silica was added in coating solution as modifier. The refractive index of this coating varied from 1.31 to 1.42. A porous antireflective (AR) silica coating with the index of 1.27 was coated on the moisture-resistant coating surface. The two-layer coating possessed transmission up to 99.1% at wavelength of 966 nm, surface root-mean-square (RMS) roughness of 1.245nm, and roughness of average (RA) of 0.961 nm. In the case of laser of 1053-nm laser wavelength and 1-ns pulse duration, the damage threshold of the two-layer coatings was more than 15 J/cm2.     

Luminescence of neodymium-doped yttria

Pulsed cathodoluminescence of Nd³⁺: Y₂O₃ nanopowders of the cubic and monoclinic phases and the ceramics synthesized from these nanopowders has been investigated in the spectral range 350–850 nm. It is found that the IR emission band of neodymium ions in the Nd³⁺: Y₂O₃ cubic phase is located at λ₁ ≈ 825 nm. When there is a monoclinic phase admixture, two additional luminescence bands of Nd³⁺ arise in the spectrum at λ₂ ≈ 750 nm and λ₃ ≈ 720 nm. The emission spectrum of all Nd³⁺: Y₂O₃ materials also contains a wide intrinsic band of yttrium oxide at λ ≈ 485 nm; however, the presence of neodymium decreases the intensity of this band and increases the its structurization. It is suggested that the structure of this band in Nd³⁺: Y₂O₃ materials is mainly determined by local absorption (self-absorption) of neodymium ions.     

Effect of lithium-potassium mixed alkali on spectroscopic properties of Er^3＋-doped aluminophosphate glasses

Er^3＋-doped lithium-potassium mixed alkali aluminophosphate glasses belonging to the oxide system xK2O-（15-x）Li2O-4B2O3-11Al2O3-5BaO-65P2O5 are obtained in a semi-continuous melting quenching process. Spectroscopic properties of Er^3＋-doped glass matrix have been analysed by fitting the experimental data with the standard Judd-Ofelt theory. It is observed that Judd-Ofelt intensity parameters Ωt（t = 2, 4 and 6） of Er^3＋ change when the second alkali is introduced into glass matrix. The variation of line strength Sed[^4I13/2,^4I15/2] follows the same trend as that of the/26 parameter. The effect of mixed alkali on the spectroscopic properties of the aluminophosphate glasses, such as absorption cross-section, stimulated emission cross-section, spontaneous emission probability, branching ratio and the radiative lifetime, has also been investigated in this paper.