Laser Host Research Articles

Enhancement of the thermal shock resistance of transparent Y2O3 ceramics by reducing the content of sintering additive

It is known that 1.0 at.% is the lowest amount of ZrO2 which can be used for the sintering of well-balanced Y2O3 ceramics to ensure both transparency and strength. In this work, a highly transparent Y2O3 ceramic material doped with a reduced amount of ZrO2 (0.5 at.%) was fabricated by means of a hot-press sintering method at a temperature as low as 1600°C using commercial powders. The in-line transmittance of the 0.5 at.% ZrO2-doped Y2O3 sample (2 mm thick) is 80.8% at 1100 nm and 72.2% at 400 nm with an average grain size of 1.06 μm. By reducing the ZrO2 content from 1.0 to 0.5 at.%, the thermal conductivity is increased by 18.2% with only a slight decline in the strength and the band gap becomes broader. Consequently, the Hasselman mild-thermal-shock figure of merit of the developed specimen increases by 13.0% overall. These results indicate that this Y2O3 ceramic has potential for use as a laser host or an infrared window material used on Mach-speed applications.

A study of optical properties of Tm3+ ions in Y2Te4O11 microcrystalline powder

The Y2-xTe4O11 (x = 0.1, 0.5, 1.0, 2.0 and 5.0 at%) microcrystalline powders were successfully synthesized by a conventional solid state reaction method. Optical absorption (300 K) and fluorescence spectra (300 K) as well as fluorescence decay curves (300 K) of the emitting levels of Tm3+ ion in Y2Te4O11 powders are presented and analyzed in details. The Judd-Ofelt theory was applied to analyze experimental data for the quantitative determination of phenomenological Ωλ (λ = 2, 4, 6) parameters, radiative transition probabilities (A), branching ratios (β) of luminescence and radiative lifetimes (τrad) of the 1D2, 1G4, 3H4 and 3F4 levels. The observed non-exponential decays nature and concentration quenching of the 1G4 and 3H4 states have been attributed to cross-relaxation processes and this phenomena has been analyzed by Inokuti-Hirayama model. The stimulated emission cross-section for the 3F4 → 3H6 transition equals to 1.12 × 10−20 cm2 at 1809 nm was calculated using the Füchtbauer-Ladenburg method and compared with the corresponding values of other Tm3+-doped laser hosts. From obtained results, follow that the Tm3+:Y2Te4O11 is a potential candidate for a solid-state laser host operating at 1.8 µm.

Experimental and first principle investigation the electronic and optical properties of YNbO4 and LuNbO4 phosphors

LnNbO4 (Ln = Y, Gd and Lu) is a type of material that can be used as both outstanding self-activated phosphor and laser host has generated significant interests. However, their electronic structures and optical properties still require elucidation. To solve this intriguing problem, firstly, YNbO4 and LuNbO4 polycrystalline with monoclinic crystal structure were prepared by traditional high-temperature solid-state reaction method and their structure and luminescent properties were characterized in experiment. Additionally, their CIE chromaticity coordinate were presented to illustrate the luminescent color and the chromaticity coordinates for YNbO4 and LuNbO4 are x = 0.1581, y = 0.0725 and x = 0.1581, y = 0.0753, respectively. Secondly, systematic theoretical calculations based on density functional theory method were carried out on them and their band structures, density of states as well as optical properties were obtained in theoretical. The calculated band gap for YNbO4 and LuNbO4 are 4.101 and 4.214 eV, respectively. Lastly, a comparison between the experimental and calculated band gap and refractive index was conducted. The good coincident between them indicating the calculated results are reliable. Therefore, all of the obtained results could provide an essential understanding of LnNbO4 materials.

Luminescent properties of Tb3+- doped TeO2-WO3-GeO2 glasses for green laser applications

Different concentrations of Tb3+ -doped oxyfluoro tellurite (TWGTb) glasses were prepared by conventional melt quenching technique and characterized for green laser applications. The Judd-Ofelt theory was applied to evaluate various spectroscopic and radiative parameters. The TWGTb glasses exhibit 5D3 → 7F5-3 and 5D4 → 7F6-0 transitions when excited at 316 nm radiation. The variation of intensity of 5D4 → 7F5 (Green) and 5D3 → 7F4 (Blue) transitions and the green to blue (IG/IB) intensity ratios were studied as a function of Tb3+ ions concentration. The laser characteristic parameters such as effective bandwidth (Δλeff), stimulated emission cross-section (σe), gain bandwidth (σe × Δλeff) and optical gain (σe × τR) were determined using the three phenomenological Judd-Ofelt intensity parameters. The fluorescence decay profiles of 5D4 metastable level exhibit single-exponential nature for all the samples. Based on the experimental results we suggest that the 1.0 mol% of Tb3+ -doped TWGTb glass could be a suitable laser host material to emit intense green luminescence at 545 nm.

The effect of excitation intensity variation and silver nanoparticle codoping on nonlinear optical properties of mixed tellurite and zinc oxide glass doped with Nd2O3 studied through ultrafast z-scan spectroscopy

The research on Nd3+ doped new solid-state laser hosts with specific thermo-mechanical and optical properties is very active. Nd3+ doped tellurite glasses are suitable for these applications. They have high linear and nonlinear refraction index, wide transmittance range. The TeO2-ZnO (TZO) glass considered in the present work combines all those features and the nonlinear optical properties can be used for the development of Kerr-lens mode-locked sub picosecond lasers. Recently the laser performance of Nd3+ doped TZO glass and was reported and laser slope efficiency of 21% was observed. We investigate how the intensity variation and the silver nanoparticles codoping affects the nonlinear optical properties of Nd3+ doped TZO glasses. Intensity dependent nonlinear refraction indices coefficients at 750, 800 and 850 nm were observed. The nonlinear optical features were obtained through ultrafast single beam z-scan technique with excitations at 750, 800 and 850 nm and are up to two orders of magnitude higher than those reported in the literature.

Fabrication of transparent Y2O3 ceramics with record-high thermal shock resistance

Sintering-additive-free fine-grained highly transparent Y2O3 ceramics featuring record-high thermal shock resistance were fabricated using commercial powders via vacuum pre-sintering (1375–1550 °C) followed by hot-isostatic pressing (1450 °C). The sample pre-sintered at 1450 °C provides the optimum microstructure for post HIPing, which resulted in a grain size of 0.64 μm. The transmittance, microhardness and fracture toughness of the thus HIPed sample are 80.8% at 1100 nm and 65.5% at 400 nm (1.2 mm thick), 8.0 ± 0.02 GPa and 1.00 ± 0.06 MPa m1/2, respectively. The thermal conductivity increases from 13.1 to 16.5 W/m/K with increasing vacuum pre-sinterin Proc. SPIE-Int. Soc. Opt g temperature from 1450 to 1550 °C. This hybrid sintering method realized high thermal conductivity and high strength simultaneously. Consequently, the thermal shock resistance of the HIPed specimen vacuum pre-sintered at 1450 °C in this work is the highest ever reported to the best of our knowledge, which makes the developed material a promising candidate for high-power laser host and IR dome.

Spectroscopic investigations of Pr3+ ions in Na2O-La2O3-ZnO-TeO2 glasses

Tellurite glasses of the composition xPr6O11–(7 − x)La2O3–3Na2O–25ZnO–65TeO2 (where x = 0.005, 0.01, 0.1, 0.2, 0.5, 1.0 and 2 mol%) were obtained by the melt quenching technique. Absorption (300 K), excitation (300 K) and fluorescence spectra (at 77 and 300 K) as well as fluorescence decay curves of the Pr3+-doped title glasses are presented and discussed. Basing on the Judd-Ofelt analysis, the phenomenological Judd-Ofelt parameters (Ω2 = 2.13, Ω4 = 16.8 and Ω6 = 3.50 × 10−20 cm2), radiative transition probabilities (AT), branching ratios (β), radiative lifetimes (τR) and emission cross-sections (σem) were calculated for the luminescence from 3P1, 3P0, 1D2 and 1G4 levels of the Pr3+ ion. The fluorescence from the 1G4 level of the Pr3+ ion has been observed after excitation at 445 nm in the 3P2 state. The experimental lifetimes of the emission levels indicate strong concentration quenching. An analysis of non-radiative decay of the 1D2 level indicate that energy migration via a diffusion limited relaxation and cross-relaxation processes are involved in the depopulation of this level. The spectroscopic results show that the investigated glasses are potentially candidates as at 1.3 μm and 1.45 μm laser host as well as reddish-orange to yellow tunable phosphor. Furthermore, a near-infrared downconversion process gives possibility of using of these materials as luminescent solar concentrators and near infrared lasers.

Eu3+-doped transparent potassium lanthanum silicate (KLaSiO4) glass-ceramic nanocomposites: Synthesis, properties and application

The preparation of Eu3+-doped novel K2O-La2O3-Al2O3-SiO2 (KLAS)-based glass and transparent KLS (KLaSiO4) glass–ceramic (GC) nanocomposites is reported. Nanostructures of the transparent GCs were analyzed by FE-SEM, H(R)-TEM and SAED techniques. The average size of the crystallites is calculated using XRD data and found to be in the range 13–19 nm which is matched well with the average particle size observed from TEM images in the range 5–18 nm. Photoluminescence spectra of Eu3+ ions exhibit emission transitions of 5D0 → 7Fj (j = 0 and 1–4) under the excitation at 394 nm. The emission spectra reveals up to 3-fold enhancement of luminescence performance of the KLS GC nanocomposites compared to as-prepared glass. This enhancement is caused due to entering of Eu3+ ions into the KLS crystal sites by replacing the La3+ ions. Such luminescence properties of KLS glass-ceramic nanocomposites could be a promising candidate as laser host for many laser devices.

A novel approach of an infrared transparent Er:Y2O3–MgO nanocomposite for eye-safe laser ceramics

Photoluminescence spectrum and energy levels of an Er:Y2O3–MgO nanocomposite.

(Lu0.3Gd0.7)2SiO5:Y3+ single crystals grown by the laser floating zone method: structural and optical studies

Laser floating zone growth of transparent Y0.05:(Lu0.3Gd0.7)2SiO5 single crystals suitable as laser host materials.

A design of a surface-doped Yb:YAG slab laser with high power and high efficiency

We demonstrate a high-efficiency and high-power quasi-three-level laser based on a trapezoidal composite slab architecture with a 270 μm-thick Yb-doping surface. The design of a surface-doped slab architecture, temperature effects, laser oscillator model, and laser oscillator experiments with a surface-doped slab as a laser host medium have been presented. By theoretical calculation, the temperature rise in the surface-doped slab is only one seventh of that in the bulk-doped slab at the same maximum pump power of 30 kW. Finally, in the laser oscillator experiments, an output energy of 21.6 J is obtained when the pump energy is 48 J with a repetition rate of 5 Hz and a pulse width of 1 ms. The optical-optical efficiency is 45%.

Chalcogenide glasses with embedded ZnS nanocrystals: Potential mid‐infrared laser host for divalent transition metal ions

AbstractChalcogenide glasses (ChGs) containing II‐VI chalcogenide (ChG) nanocrystals such as ZnS/Se have recently been intensively studied as promising mid‐infrared nonlinear optics and laser materials, yet preparation of pure‐phase II‐VI nanocrystals embedded in ChGs via controlled crystallization is still very challenging. In this study, a new system of ChGs and glass ceramics (GCs), viz., (100−x)As2S3–xZnSe (x = 0 ~ 30 mol%), is synthesized, and its physical and optical properties including density, molar volume, microhardness, glass transition temperature, glass network structure, transmission, and refractive index are comprehensively characterized. Significantly, it is initially demonstrated that pure ZnS nanocrystals can be precipitated in GCs simply by a thermal treatment process. The composition and thermal treatment temperature dependencies of crystallization are studied using X‐ray diffraction spectroscopy, and the morphology of the nanocrystals by high‐resolution transmission electron microscope. The ChG GCs with embedded ZnS nanocrystals retaining good transparency can be a potential host laser material for divalent transition metals (e.g., Cr2+/Fe2+, etc.), and thus used for ultrabroadband tunable continuous or ultra‐short‐pulsed mid‐infrared fiber lasers.

Crystal growth and characterization of undoped and Dy-doped TlPb2Br5 for infrared lasers and nuclear radiation detection

We report results of the crystal growth and characterization of undoped and Dy-doped TlPb2Br5 for applications in infrared (IR) lasers and nuclear radiation detection. TlPb2Br5 (TPB) was synthesized from commercial starting materials of PbBr2 and TlBr and further purified through a combination of zone-refinement and directional solidification. For doping experiments, 2 wt% of DyBr3 was added to the purified TPB material. Crystal growth of TPB and Dy: TPB was carried out in a two-zone tube furnace by a vertical Bridgman method. Following optical excitation at ∼1.36μm, the Dy: TPB crystal exhibited efficient mid-IR emission bands centered at 2.87μm and 4.35μm with room-temperature lifetimes of 9.5ms and 5.2ms, respectively. The peak emission cross-sections were determined to be ∼0.8×10−20cm2 and ∼0.5×10−20cm2, respectively, which makes Dy: TPB a promising candidate for mid-IR laser applications. Besides its potential as a solid-state laser host, an undoped TPB crystal was also tested for gamma-ray detection. Using Cs-137 and Am-241 sources resulted in energy resolutions for gamma-rays as good as 1–2% (FWHM) at room-temperature under non-optimized conditions.

2.3 µm laser potential of TeO2 based glasses

Tm3+ doped TeO2-based well-dehydrated glasses were synthesized and investigated. The analysis of their spectral and relaxation properties have showed that these glasses can be a suitable host for bulk and fiber lasers emitting at ~2.3 µm wavelength (3H4–3H5 Tm3+ transition). Laser action in the bulk glass sample was demonstrated.

Spectroscopic investigations of 1.06 µm emission and time resolved Z-scan studies in Nd3+-doped zinc tellurite based glasses

Zinc tellurite based glasses (TZNbTiNd: TeO2 + ZnO + Nb2O5 + TiO2) doped with various Nd3+ concentrations (0.01, 0.05, 0.1, 0.5, 1.0, 1.5 and 2.0mol% Nd2O3) were prepared and characterized through absorption, emission and decay rate measurements. Judd-Ofelt intensity parameters were derived from the absorption spectrum and used to calculate the radiative properties for the 4F3/2 → 4IJ/2 (where J = 9, 11 and 13) transitions of Nd3+ ions. Strong near infrared emission at 1.062µm (4F3/2 → 4I11/2) has been obtained for all the glasses upon 808nm diode laser excitation. The decay times from 4F3/2 level is found to be quite single exponential for different concentrations of Nd3+ ions with a shortening of lifetime with increasing concentration. In these measurements, the electronic refractive index variation is associated with the difference in the polarizabilities (Δαp) of the Nd3+ ion in its ground and excited states. The results indicate that in tellurite glasses, Δαp is relatively very high (4 × 10−25cm3) compared to other Nd3+-doped glasses. We also measured the imaginary part of the non-linear refractive index (n2′′) due to absorption saturation. Hence, the spectroscopic results indicate that the investigated glasses are potentially applicable as a 1062nm laser host as well as optical devices.

Synthesis and properties of Nd-doped oxynitride phosphate laser glasses

The substitution of nitrogen for oxygen in phosphate glasses improves the chemical, thermal and mechanical properties and particularly reduces their very high hygroscopic character, although the preparation of homogeneous and free of defects oxynitride bulk phosphate glasses through ammonolysis represents a big challenge. This work reports on the synthesis and properties of a series of Nd-doped oxynitride phosphate glasses with composition Na0.3K0.3Ba0.2PO3-3x/2Nx that may find application as laser hosts. Whereas the glass transition temperature, elastic modulus and index of refraction show a regular increase with the nitrogen content that agrees with previous studies, the effect of nitrogen onto the luminescence of Nd3+ ions appears to be more complicated. The average lifetime of the decay from the 4F3/2 level decreases with the N/P ratio of the glasses, which is thought to be mainly due to the presence of water from the ammonolysis reaction. However, further thermal treatments under N2 flow of an oxynitride glass have shown an important reduction of the water content as well as a drastic increase of the luminescence lifetime of Nd3+, this being a promising method for the development of laser phosphate glasses having good chemical and mechanical properties.

Sellmeier equations, group velocity dispersion, and thermo-optic dispersion formulas for CaLnAlO4 (Ln = Y, Gd) laser host crystals.

We studied the refractive index and dispersive properties of the tetragonal rare-earth calcium aluminates, CaLnAlO4 (Ln=Gd or Y). Sellmeier equations were derived for the spectral range of 0.35-2.1μm. The group velocity dispersion (GVD) in CaGdAlO4 is positive at ∼1 μm, 95 fs2/mm and negative at ∼2 μm, -40 fs2/mm. The GVD values for CaYAlO4 are similar. In addition, thermo-optic coefficients, dn/dT, and thermal coefficients of the optical path were determined for CaYAlO4. dn/dT is negative at ∼1 μm, dno/dT=-7.8, and dne/dT=-8.7×10-6 K-1. Thermo-optic dispersion formulas were constructed. The obtained data are of key importance to the design of high-power mode-locked oscillators at ∼1 and ∼2 μm based on such laser hosts.

Optical and spectroscopic properties of neodymium doped cadmium-sodium borate glasses

Neodymium doped cadmium sodium borate glasses having composition xCdO-(40-x) Na2CO3-59.5H3BO3-0.5Nd2O3; x=10, 20 and 30mol% were prepared by conventional melt-quenching technique. X-ray diffraction studies confirmed the amorphous nature of the prepared glasses. Conventional methods were used to determine the physical properties such as density, molar volume, refractive index, and rare earth ion concentration. The Judd-Ofelt theory was applied on the optical absorption spectra of the glasses to evaluate the three phenomenological intensity parameters Ω2, Ω4 and Ω6. The calculated intensity parameters were further used to predict the radiative transition probability (A), radiative lifetime (τR) and branching ratio (βR) for the various fluorescent levels of Nd3+ ion in the prepared glass series. The effect of the compositional changes on the spectroscopic characteristics of Nd3+ ions have been studied and reported. The value of Ω2 is found to decrease with the decrease in the sodium content and the corresponding increase in the cadmium content. This can be ascribed to the changes in the asymmetry of the ligand field at the rare earth ion site and the change in rare earth oxygen (RE-O) covalency. Florescence spectra has been used to determine the peak wavelength (λp), effective line widths (Δλeff) and stimulated emission cross-section (σp) for the 4F3/2→4I9/2,4I11/2,4I13/2 transitions of the Nd3+ ion. The reasonably higher values of branching ratios and stimulated emission cross-section for the prepared glasses points towards the efficacy of these glasses as laser host materials. However, the glass with more sodium content is found to show better lasing properties.

Polarized spectral properties of Sm:CaGdAlO4 crystal for reddish-orange laser

The crystal growth, polarized spectral properties, Judd-Ofelt (JO) analysis and lifetime of Sm:CaGdAlO4 (Sm:CGA) crystal were reported for the first time. Sm:CGA crystal with size of Φ4 × 33 mm3 was grown by the floating zone (FZ) method. The peak absorption cross-sections at 407 nm were calculated to be 3.41 × 10−20cm2 and 3.20 × 10−20cm2 for the σ and π polarization, and the largest stimulated emission cross-sections at 601 nm were 5.10 × 10−21cm2 and 4.66 × 10−21cm2, respectively. The absorption and emission cross-sections were several times larger than that of Sm:LiYF4. The JO intensity parameters of Ω2, Ω4 and Ω6 were calculated to be 3.0 × 10−20cm2, 6.1 × 10−20cm2 and 6.5 × 10−20cm2, respectively. The lifetime of the 4G5/2 level was obtained to be 0.69 ms. All the results indicate that Sm:CGA crystal is a potential laser host for the reddish-orange laser operation.

Random laser emission from a Rhodamine B-doped GPTS/TEOS-derived organic/silica monolithic xerogel

A Rhodamine B-doped 3-glycidoxypropyltrimethoxysilane (GPTS)/tetraethyl orthosilicate (TEOS)-derived organic/silica monolithic xerogel with excellent optical properties was prepared and its potential as a random laser host investigated. This hybrid material has a non-porous organic/inorganic morphology with silica-rich nanoparticles of less than 10 nm in diameter homogeneously dispersed within the matrix. Random laser emission with incoherent feedback, centered at 618 nm, was observed from Rhodamine B incorporated into the monolithic xerogel when excited by a 532 nm pulsed laser. This hybrid system is shown to be very promising for the development of a new class of random laser-based integrated devices, with applications ranging from optical bio-imaging to sensing.