Nd-doped Glass Research Articles

Thermal and Optical Properties of ${\hbox {Yb}}^{3+}$- and ${\hbox {Nd}}^{3+}$-Doped Phosphate Glasses Determined by Thermal Lens Technique

In this work, we study the thermal and optical properties of ion-doped phosphates glasses using the thermal lens (TL) technique. Three samples were characterized: Nd3+-doped Q-98; Nd3+-doped Q-100; and Yb3+-doped QX. We report multiwavelength TL measurements for a more accuracy determination of the fluorescence quantum efficiency and temperature coefficient of the optical path length change (ds/dT). In Nd-doped glasses, it was carried out using four discrete excitation wavelengths (between 514 and 872 nm) chosen to match with the ion absorption lines. In Yb-doped glass, the spectrum of heat generated along the Yb3+ transition (2 F 5/2rarr2 F 7/2) was obtained. In addition, parameters as thermal diffusivity and conductivity, thermal loading, etc were achieved. The advantages to obtain fluorescence quantum efficiency using the TL technique, mainly in Yb3+ doped materials, which are normally overestimated due to radiation trapping effect, are presented. The accuracy knowledge of these parameters is very important for design of high-power solid-state lasers, since these properties are directly related to the heat generation.

40 J class laser oscillation of Nd-doped silica glass with high thermal shock parameter

The authors demonstrated a 40J class laser oscillation from a bulk-type Nd-doped silica glass with a high thermal shock parameter. A maximum output energy of 37.3J was obtained from a laser oscillator that consisted of a 30% output coupler with a 30mm diameter and 300mm length laser medium. The thermal shock parameter, a figure of merit for the thermal toughness of the materials, was estimated to be 12.0W∕cm, which is 1.5 times larger than neodymium-doped yttrium aluminum garnet (7.9W∕cm). These results show that the Nd-doped silica glass has the potential to be installed in high-average-power or high-peak-power lasers.

Deviations from the reciprocity theory of McCumber at low temperature in Nd3+-doped glasses

The reciprocity theory of McCumber [Phys. Rev. 136, A954 (1964)], which relates optical absorption and emission spectra between two energy level manifolds, was tested at temperatures down to 130K on the F3∕24→I9∕24 transition in Nd-doped glass. Deviations between calculated and measured spectra were observed for temperatures below 230K in Nd:silicate and below 170K in Nd:fluorozirconate glass. Below these temperatures, the calculated absorption is skewed to shorter wavelength and the calculated emission is skewed to longer wavelength. The magnitude of the deviation depends on the ratio of inhomogeneous linewidth to thermal energy kBT.

Nd-doped oxyfluoroborate glasses and glass-ceramics for NIR laser applications

Fluorescence at 1.06 μm due to main 4F3/2–4I11/2 laser transition of Nd3+ ions in multicomponent B2O3–PbF2–PbO–Al2O3–WO3 glass system has been registered and some laser parameters for Nd3+ ions have been evaluated. The Nd-doped oxyfluoroborate glasses have been investigated as a function of PbF2 concentration and thermal treatment. The fluorescence decays from 4F3/2 excited state of Nd3+ ions are independent on PbF2 concentration. The orthorhombic PbF2 phase has been identified for Nd-doped transparent glass-ceramics obtained after thermal treatment.

Analytical study for investigating the behaviour of Nd-doped Glass, YAG and GGG under the heat capacity mode of operation

In this paper, detailed analytical studies on heat capacity operation in Nd-doped glass, YAG and GGG has been reported. The effect of the rising temperature on gain and hence on the output energy/power has been numerically worked out. The studies predicted that several kilowatts of the useful output power can be extracted out from the laser materials under investigation when operated under the heat capacity mode. The studies also revealed that output power levels can be scaled up by increasing the number of disks and by increasing the disk aperture size. The factors limiting the power enhancement are also discussed. The estimated results are in good agreement with the other reported experimental results.

Laser Oscillation of Nd-Doped Silica Glass with High Thermal Shock Parameter

Laser oscillation with the input/output characteristics of bulk-type Nd-doped silica glass with a high thermal shock parameter was demonstrated for the first time. The thermal shock parameter was estimated to be 12.0 W/cm, which is 1.5 times larger than that of Nd:YAG crystal (7.9 W/cm). The maximum output energy of 154 mJ was obtained with an output mirror of 20% transmittance. Although the output energy was 154 mJ, if without loss, output energy increases up to 1.69 J, eleven times larger than the present state. These results mean that Nd-doped silica glass can work as a high-average or a high-peak-power-laser.

Mean free path for excitation energy migration in Nd3+-doped glasses as a function of concentration

The energy-transfer process and the related migration mechanism of excitation energy, important in the optical dynamics of Nd-doped glasses, were investigated. In order to study the migration mechanism and transfer process, Nd3+-doped oxide glasses were produced with doping concentration (N) ranging from 0.1to1.9wt% as Nd2O3. A microluminescence technique was used to measure the spatial distribution of the emitting light as a function of the distance from the center of the laser-excitation spot with different Nd3+-ion concentrations. Efficient long-range migration of excitation energy of Nd3+ ions was observed at 1.1wt% of Nd2O3. The critical distance between Nd3+ ions, estimated from the observed migration length, shows that dipole-dipole interaction is not the dominant mechanism for energy transfer. The mean free path for migratory excitation energy in the investigated material, assisted by absorption and scattering by defects or phonons, is the most probable mechanism for energy transfer.

Polishing slurry induced surface haze on phosphate laser glasses

The effects of residual polishing slurry on the surface topology of highly polished, Nd-doped meta-phosphate laser glasses are reported. Glass samples were pitched polished using cerium oxide or zirconium oxide slurry at different pHs and then washed by different methods that allowed varying amounts of residual slurry to ‘dry’ on the surface. Upon rewashing with water, some of the samples showed surface haze (scatter), which scaled with the amount of residual slurry. Profilometry measurements showed that the haze is the result of shallow surface pits (100 nm–20 μm wide × ∼15 nm deep). Chemical analyses of material removed during rewashing, confirmed the removal of glass components as well as the preferential removal of modifier ions (e.g., K 1+ and Mg 2+). The surface pits appear to result from reaction of the glass with condensed liquid at the slurry particle–glass interface that produces water-soluble phosphate products that dissolves away with subsequent water contact. Aggressive washing, to remove residual slurry immediately following polishing, can minimize surface haze on phosphate glasses. It is desirable to eliminate haze from glass used in high-peak-power lasers, since it can cause scatter-induced optical modulation that can cause damage to downstream optics.

Development of Nd-doped Optical Gain Material Based on Silica Glass with High Thermal Shock Parameter for High-Average-Power Laser

In this paper, we report a demonstration of amplification at 1.06 µm in a bulk-type Nd-doped silica glass (Nd2O3: 1.25 wt%, Al2O3: 2.72 wt%, SiO2: 96.03 wt%) with a high thermal shock parameter for the first time. The optical gain of 1.75 was obtained in a 93-mm-long sample with a flash lamp pumping at 1.9 kJ, corresponding to a gain coefficient of 0.06 cm-1. The thermal shock parameter of Nd-doped silica glass was measured to be 12.0 W/cm, which is thirty times greater than that of phosphate glass and one and a half times greater that of Nd:YAG. We carried out a quick quenching experiment to determine the thermal shock toughness of Nd-doped silica glass, and the experiment demonstrated that the thermal shock toughness of Nd-doped silica glass was superior to that of the phosphate laser glass. We also calculated the thermal stress distribution in Nd-doped silica glass with a simple model for comparison with the experimental results; the model well explains the experimental results. These results indicate that Nd-doped silica glass can produce a compact, high-energy density, and high-average-power laser.

Spectroscopic and glass transition investigations on Nd 3+-doped NaF–Na 2O–B 2O 3 glasses

New developments in photonic technology need new materials for various applications. In the present report, Nd 3+-doped NaF–Na 2O–B 2O 3 glasses were prepared and the spectroscopic and glass transition properties were analysed. The Fourier transform infrared spectral studies reveal that the glass contains BO 3 and BO 4 units as the local structures and the Na + ions as the network modifiers. The absorption studies were carried out by using Judd–Ofelt theory, the experimental and theoretical oscillator strengths were also calculated. The emission spectral study was done for the 1 mol% Nd-doped glass and the spontaneous emission probability and stimulated emission cross-sections for the 4 F 3/2→ 4 I 9/2 , 4 I 11/2 transitions were calculated using the J–O parameters.

Structure of Nd-doped glasses measured by isotopic substitution in neutron diffraction

The structural environment of Nd ions in glasses can have a significant effect on their performance in optical devices. Isotopic substitution in neutron diffraction has been used to probe the structure of Nd2O3 doped SiO2 and La2O3+Y2O3+Al2O3 glasses. In the silicate glass, Nd is found to be ∼sixfold coordinated by oxygen atoms at a distance of 2.28(2) Å with additional Nd–O/Si correlations at 3.55(3), 4.78(3), 5.89(3) Å, and higher distances. In the rare-earth aluminate glass a peak at 2.49(2) Å and a shoulder at ∼3 Å indicate the presence of 8 or higher coordinate Nd polyhedra by comparison with bond valence theory.

Study on the laser-induced darkening in Nd-doped laser glasses

Laser induced darkening in the soda-lime silicate (15Na 2 O · 15CaO · 70SiO 2 ) based glass and type N 31 barium metaphosphate Ba(PO 3 ) 2 based glass were studied by exposing the glass samples in frequency-quadrupled Nd:YAG (266 nm, 5 ns) laser and Ti:Sapphire (800 nm, 120 fs) laser. Both types of the glasses were doped with Nd 2 O 3 at doping levels less than 3 wt%. Hole center HC 1 formed after UV laser exposure in soda-lime silicate based laser glass, and both HC 1 hole center and SiE ′ center formed in it after IR fs laser irradiation. In phosphate glass, UV ns laser and IR fs laser generated the same types of color centers, intermediate structure of oxygen ions type II and type III. The experimental results also showed that the soda-lime silicate laser glass is easier to be darkened than the phosphate glass, irradiated by either 266 nm UV laser or fs laser. While free electrons from single photon ionization is considered to be the main cause of defect formation in glasses irradiated by nanosecond UV laser, rapid cooling of the melted glasses heated by energetic electrons generated from multi-photon and avalanche ionization should be the causes of defect formation in glasses irradiated by fs laser.

Exploration of self-writing and photosensitivity in ion-exchanged waveguides

We have demonstrated that self-written channel waveguides can be formed reproducibly in K+-ion-exchanged Nd-doped Bk7 glass by making use of a photosensitive index change of ∼6×10-5 induced by illumination at 457 nm. The guidance characteristics of these waveguides have been investigated from 457 to 1550 nm. Detailed experiments have been carried out by exploration of the self-writing process, and these are also used to investigate the photosensitivity of the material. We find that an intensity threshold exists below which photosensitivity does not occur. Numerical simulations of both the evolution and the guidance properties of the self-written waveguides provide excellent agreement with observations.

Phase-locked antiguided multiple-core ribbon fiber

We report on the first experimental demonstration of a scalable fiber laser approach based on phase-locking multiple gain cores in an antiguided structure. A novel fabrication technology is used with soft glass components to construct the multiple core fiber used in our experiments. The waveguide region is rectangular in shape and comprised of a periodic sequence of gain and no-gain segments having nearly uniform refractive index. The rectangular waveguide is itself embedded in a lower refractive index cladding region. Experimental results confirm that our five-core Nd-doped glass prototype structure runs predominately in two spatial antiguided modes as predicted by our modeling.

Nd-doped tellurite glass microsphere laser

Continuous-wave oscillation in a Nd-doped tellurite glass microsphere laser at 1.06 /spl mu/m has been successfully demonstrated for the first time. Microspheres with diameters of 50 to a few hundred micrometres are fabricated by melting using an electric heater. Emission spectra reveal that the devices exhibit resonances corresponding to whispering gallery modes.

Formation of the spectra of multiply charged ions from the plasma of Nd-doped glass irradiated with a neodymium laser

The effect of neodymium ions on laser-induced glass destruction and the formation of the spectra of laser plasma ions is studied by the mass-spectrometric and optical-microscopy methods. As the Nd ion concentration increases, the degree of laser-induced damage in silicate glass increases, the threshold intensity for the glass destruction decreases, the maximum ion charge number Zmax and the maximum ion energy Emax decrease, and the energy spectra of target ions change. All this is related to both the coincidence between the lasing lines and the absorption bands of Nd ions and the intensifi cation of recombination processes in the multicomponent laser plasma.

Observation of light-induced refractive index reduction in bulk glass and application to the formation of complex waveguides

We show that illuminating bulk Nd-doped Bk7 glass at 488 nm induces a decrease in refractive index of order 10(-4). Using this index change we experimentally demonstrate that it is possible to use self-writing to enhance the divergence of a Gaussian beam.Here simulations with a Laguerre-Gaussian 'donut' writing beam show that a depressed-index 'pipe' structure can be created.We demonstrate that these complex waveguide structures can subsequently be used to guide light of different wavelengths.

Microstructural and spectroscopic study of sol–gel derived Nd-doped silica glasses

Nd-doped silica glasses have been prepared from a base catalyzed sol–gel solution. The photoluminescence (PL) spectrum and lifetime of the glasses have been studied with respect to their microstructure and chemical composition. It is shown that the glass microstructure depends closely on the solution pH and Nd-doping. A slow decay component (SDC) of the 1060 nm PL, with a lifetime of around 300 μs, and a fast decay component (FDC), with a lifetime of around 0.3 μs, have been identified. The FDC is attributed to Nd 3+ ions clusterization inside the silica matrix. It has been shown that the FDC can be almost extinguished and the SDC component substantially increased by Al co-doping. The reasons are twofold: (i) inhibition of the Nd 3+ ions clusterization and (ii) intrinsically better PL efficiency of Al co-doped glasses at 1060 nm. Depending on the solution pH, the amount of Nd in the glass can be noticeably increased while preventing a detrimental rare earth clusterization. Thus, a greater glass PL efficiency can be expected.

Upconversion losses in Nd-doped fluoroarsenate glasses

In this work we report the infrared to visible upconversion processes in Nd-doped fluoroarsenate glasses that produce green, orange, and red emissions together with the dynamics of the 4F 3/2 state. The visible emissions can be attributed to transitions from the 4G 7/2 excited state populated by energy transfer upconversion (ETU). It was found that ETU processes involving two Nd 3+ ions in the 4F 3/2 state reduce the energy storage capacity through the reduction of the fluorescence lifetimes of the 4F 3/2 state. From the analysis of the temporal evolution of the infrared emission from the 4F 3/2 state we have estimated the macroscopic ETU parameter for the samples studied.

Low-frequency dynamics of a Nd-doped glass laser

We study a Nd-doped microchip glass laser that emits in two polarizations and in many longitudinal modes. Saturation of the inversion by standing waves causes spatial inhomogeneity of both the longitudinal and azimuthal distributions of the laser gain. These nonlinear inhomogeneities couple the modes and result in low-frequency oscillations (10\char21{}500 kHz) of the light flux in the individual laser modes. These oscillations are steadily driven by quantum noise and appear as 15% fluctuations of the power in each mode. In-phase fluctuations in the laser modes appear at the frequency of the main relaxation oscillation of the total laser power. Antiphase fluctuations appear at other frequencies in individual longitudinal and polarization laser modes only. The dominant frequency of these fluctuations is determined by the light power in the mode. Numerical simulations of rate equations, including Langevin forces, satisfactorily reproduce the experimental results. These phenomena must be taken into account when lasers are applied as stable coherent optical light sources, and also with sensitive absorption measurements in the laser cavity.