High Tm3 Research Articles

Broadband high-gain Tm3+/Ho3+ co-doped germanate glass multimaterial fiber for fiber lasers above 2 µm.

High-gain Tm3+/Ho3+ co-doped optical fibers are urgently desired for high-repetition-rate mode-locked fiber lasers at >2 µm. Here, Tm3+/Ho3+ co-doped germanate glass with low hydroxyl (OH-) content was prepared by the conventional melt-quenching method combined with the reaction atmosphere procedure (RAP) dehydration technique. The doping concentrations of Tm2O3 and Ho2O3 are 2.5 mol.% (7.1 wt.%) and 0.25 mol.% (0.7 wt.%), respectively. Thanks to the high Tm3+ doping (7.1 wt.%) and low energy transfer efficiency (19.8%) between Tm3+ and Ho3+ ions, it enables achieving broadband and high-gain performance in the 2 µm region. Then a silicate-clad Tm3+/Ho3+ co-doped germanate core multimaterial fiber was successfully drawn by using the rod-in-tube method, which has a broadband amplified spontaneous emission (ASE) with a full width at half-maximum (FWHM) of 247.8 nm at 2 µm. What is more, this new fiber has a high gain per unit length of 4.52 dB/cm at 1.95 µm. Finally, an all-fiber-integrated passively mode-locked fiber laser was built by using this broadband high-gain fiber. The mode-locked pulses operate at 2068.05 nm, and the fundamental repetition rate is up to 4.329 GHz. To the best of our knowledge, this is the highest fundamental repetition rate for the all-fiber passively mode-locked fiber laser above 2 µm. These results suggest that the as-drawn multimaterial fibers with broadband high-gain characteristics are promising for high-repetition-rate ultrafast fiber lasers.

Characterization of oxyfluoride glasses doped with rare-earth ions through structural, thermal, and optical application thereof

Novel transparent glasses and glass-ceramics were fabricated by using melt-quenching technique with the following composition: TeO2–WO3–Nb2O5–KF–La2O3 doped with Tm2O3. Different properties and physical parameters of these glasses were investigated. As the concentration of Tm3+ ions increases, the linear refractive index increases while the optical energy gap decreases. With high Tm3+ ion concentration creates nucleation in the glass matrix this was investigated by x-ray diffraction. The Judd-Ofelt parameters used to calculate the electric and magnetic dipole transition probabilities, branching ratios, and radiative lifetimes of various excited states of Tm3+-doped parent glass. The emission cross section values for the 3F4→3H6 transition computed by using the McCumber hypothesis. The stimulated emission cross section σeFL(λ) and gain values of fabricated glass increase with Tm3+ ions. The spectroscopic quality and figure of merit (FOM) gain (σeFL(λ)×τR) factors were evaluated for the prepared transparent glass. Furthermore, the produced glasses were demonstrated to have low OH content and they have high fluoride ion content. These important properties of the glasses and glass-ceramics make them suitable for use in photonic applications.

The preparation of Yttrium Aluminosilicate (YAS) Glass Fiber with heavy doping of Tm3+ from Polycrystalline YAG ceramics

AbstractYttrium aluminosilicate (YAS) glass core fibers with different doping concentration of Tm3+ were fabricated by a “Melt‐in‐Tube” method from YAG polycrystalline ceramics. The effect of Tm3+ concentration on the spectroscopy of YAG ceramics and laser performance of YAS fibers were discussed. A homemade linear all‐fiber laser based on the obtained 15% Tm3+‐doped YAS fiber shows an optimized slope efficiency of 12.8%. The YAS fibers have been proven to be practical to achieve extremely high Tm3+ doping concentration and are a promising option for the 2.0 μm laser.

Amplified stimulated emission in upconversion nanoparticles for super-resolution nanoscopy.

Lanthanide-doped glasses and crystals are attractive for laser applications because the metastable energy levels of the trivalent lanthanide ions facilitate the establishment of population inversion and amplified stimulated emission at relatively low pump power. At the nanometre scale, lanthanide-doped upconversion nanoparticles (UCNPs) can now be made with precisely controlled phase, dimension and doping level. When excited in the near-infrared, these UCNPs emit stable, bright visible luminescence at a variety of selectable wavelengths, with single-nanoparticle sensitivity, which makes them suitable for advanced luminescence microscopy applications. Here we show that UCNPs doped with high concentrations of thulium ions (Tm3+), excited at a wavelength of 980 nanometres, can readily establish a population inversion on their intermediate metastable 3H4 level: the reduced inter-emitter distance at high Tm3+ doping concentration leads to intense cross-relaxation, inducing a photon-avalanche-like effect that rapidly populates the metastable 3H4 level, resulting in population inversion relative to the 3H6 ground level within a single nanoparticle. As a result, illumination by a laser at 808 nanometres, matching the upconversion band of the 3H4 → 3H6 transition, can trigger amplified stimulated emission to discharge the 3H4 intermediate level, so that the upconversion pathway to generate blue luminescence can be optically inhibited. We harness these properties to realize low-power super-resolution stimulated emission depletion (STED) microscopy and achieve nanometre-scale optical resolution (nanoscopy), imaging single UCNPs; the resolution is 28 nanometres, that is, 1/36th of the wavelength. These engineered nanocrystals offer saturation intensity two orders of magnitude lower than those of fluorescent probes currently employed in stimulated emission depletion microscopy, suggesting a new way of alleviating the square-root law that typically limits the resolution that can be practically achieved by such techniques.

Effect of Tm³⁺ Concentration and Temperature on Blue and NIR Upconversion Luminescence in Tm³⁺/Yb³⁺ Co-Doped NaY(WO₄)₂ Microstructures.

Tm³⁺/Yb³⁺ codoped NaY(WO₄)₂ microstructures with various Tm³⁺ concentrations and 10 mol% Yb³⁺ concentration were prepared by a microwave-assisted hydrothermal method, and their upconversion luminescence (UCL) was investigated. Under excitation at 980 nm, Tm³⁺/Yb³⁺ codoped NaY(WO₄)₂ exhibited strong blue and near infrared (NIR) emissions, respectively, corresponding to ¹G₄ --> ³H₆ and ³H₄ --> ³H₆ transitions, with weak red emission due to the ¹G₄ --> ³H₄ transition. The optimum doping concentrations of Tm³⁺ for the highest blue and NIR UCL were investigated, and it was found that the optimal concentrations for blue and NIR emissions were 0.5 mol% and 1.5 mol%, respectively. In addition, an analysis of temperature dependent blue and NIR UCL in both the samples with low and high Tm³⁺ concentrations, respectively, was undertaken. The results implied that the sample with low Tm³⁺ concentration displayed more obvious effect on the thermal quenching of ¹G₄ level.

Spectroscopic properties of Tm3+/Al3+ co-doped sol–gel silica glass

Tm3+/Al3+ co-doped silica glass was prepared by sol–gel method combined with high temperature sintering. Glasses with compositions of xTm2O3–15xAl2O3–(100−16x) SiO2 (in mol%, x=0.1, 0.3, 0.5, 0.8 and 1.0) were prepared. The high thulium doped silica glass was realized. Their spectroscopic parameters were calculated and analyzed by Judd–Ofelt theory. Large absorption cross section (4.65×10−21cm2 at 1668nm) and stimulated emission cross section (6.00×10−21cm2 at 1812nm), as well as low hydroxyl content (0.180cm−1), long fluorescence lifetime (834μs at 1800nm), large σem×τrad (30.05×10−21cm2ms) and large relative intensity ratio of the 1.8μm (3F4→3H6) to 1.46 (3H4→3F4) emissions (90.33) are achieved in this Tm3+/Al3+ co-doped silica glasses. According to emission characteristics, the optimum thulium doping concentration is around 0.8mol%. The cross relaxation (CR) between ground and excited states of Tm3+ ions was used to explain the optimum thulium doping concentration. These results suggest that the sol–gel method is an effective way to prepare Tm3+ doped silica glass with high Tm3+ doping and prospective spectroscopic properties.

Microwave-assisted hydrothermal synthesis and laser-induced optical heating effect of NaY(WO_4)_2:Tm^3+/Yb^3+ microstructures

Tm3+/Yb3+ codoped NaY(WO4)2 microstructures with various Tm3+ concentrations and 10 mol% Yb3+ concentration and 1 mol% Er3+/10 mol% Yb3+ codoped NaY(WO4)2 microstructure were prepared via a microwave-assisted hydrothermal reaction. The crystal structure and microscopic morphology of the products were characterized by means of XRD and FM-SEM. Er3+/Yb3+ doped NaY(WO4)2 microstructure was used as temperature sensing probe for studying on the laser heating behavior in Tm3+/Yb3+ doped NaY(WO4)2 microstructures. It was found that higher laser excitation density resulted in higher sample temperature, and the sample with higher Tm3+ doping concentration exhibited more obvious heating effect when excited by 980 nm laser. Moreover, the time scanning upconversion spectra displayed that the upconversion luminescence intensities for both the samples with low and high Tm3+ concentrations almost unchanged with 980 nm laser irradiation time when the excitation power density was lower, but decreased greatly when the excitation power density was higher, and the sample with low Tm3+ concentration displayed larger luminescence intensity change rate. This phenomenon was explained by Arrhenius’s model for the thermal quenching process.

Expanding broadband emission in the near-IR via energy transfer between Er3+–Tm3+ co-doped tellurite-glasses

Processes of energy transfer in Er3+–Tm3+ co-doped tellurite glasses has permitted to obtain an expanding broadband emission in the near-infrared region covering the bands S, C+L and U of the optical telecommunications and extending up to the 1700–1900nm range under excitation by a 976nm laser diode. This widening of the emission band is achieved through an integrated emission, where the Er3+ ions act as donor and the Tm3+ ions as acceptor following the route (Er3+)4I11/2→(Tm3+)3H5, (Er3+)4I13/2→(Tm3+)3H4 and (Er3+)4I13/2→(Tm3+)3F4. The relative intensity emission and lifetime of the 4I13/2→4I15/2 transition of the Er3+ ions decrease with increasing the Tm3+ concentration. Besides, high Tm3+ concentrations produce an emission quenching for the 3H4→3F4 and 3F4→3H6 radiative transitions, due to cross-relaxation between Tm3+ ions. These effects are studied by means of probability and quantum yield of the energy transfer. The most intense and widest emission band is measured in the glass co-doped with 0.075 and 1mol% of Tm2O3 and Er2O3, respectively.

Thulium Doped Phosphors Under VUV Excitation

AbstractDevelopment of highly efficient mercury free fluorescent lamps and plasma display panels has been a challenging task due to the need for a combination of phosphor properties that are difficult to obtain in a single material (high efficiency, short emission lifetime and weak sensitivity to aging process under VUV excitation). Quantum cutting mechanism is a way to improve the fluorescence efficacy. Here we describe quantum cutting involving pairs of Tm3+ ions in KY3F10. Efficient excitation in the vacuum UV is initiated to the 5d state of Tm3+. This is followed by a cross relaxation energy transfer (CRET) involving the excited ion in the 5d state and nearby Tm3+ in the ground state, producing a pair of Tm3+ in excited states of the 4f13 configuration. Both ions can then emit photons. The excitation and reflection spectra are studied as a function of Tm3+ concentration and temperature. An unusual enhancement of the reflectivity at excitation wavelengths corresponding to the Tm3+ 5d absorption peaks is shown to arise from strong 5d→4f emission which is confirmed from the VUV emission spectra. The strong reduction of the integrated 5d emission intensity and shortening of its lifetime with Tm3+ concentration indicates the effective presence of the desired CRET process that is required for the first step of the quantum cutting. High Tm3+ concentrations are required for efficient quantum cutting. Whereas the CRET from the 5d state is estimated to be quite efficient, the 4f13 states of Tm3+ also undergo a strong CRET and therefore, emission from the 4f13 excited states that are created from the first step are strongly quenched at high Tm3+ concentrations. As a result, quantum yields greater than unity are not achieved.

Gain-shifted TDFA employing high concentration doping technique with high internal power conversion efficiency of 70%

The amplification characteristics of a high Tm3+ concentration doped gain-shifted Tm-doped fluoride fibre amplifier (GS-TDFA) have been determined with a high input signal power. This GS-TDFA achieved the highest reported internal power conversion efficiency of 70%.

Blue Upconversion Characteristics of Thulium-doped Silica Fiber with High Germania Content

Intense blue upconversion luminescences were observed in a high-NA silica fiber doped with Tm3+ and 25mol% GeO2 by pumping with a 630-670nm laser. The intensities of two bands due to the 1D2 → 3F4 at 455nm and 1G4 → 3H6 transition at 480nm were changed with the pumping wavelength, power, and the fiber length. These phenomena were ascribed to the population inversion of the3F4 excited state to the ground state and large population of the 3H4, that are the intermediate excited levels for the 3G4 and 1D4 upconversions, respectively. The nonlinear power dependence of the population could be due to the relatively low-phonon-energy, high Tm3+-concentration and high pump-power density in the core of this high-NA fiber. The peak shift of the 480nm-band with the fiber length and a two-photon process of 1.2 µm luminescence band are also discussed.