Μm In Tm3 Research Articles

Fluorescence and Physical Properties of Tm3+/Ho3+ Co-Doped Tellurite Glasses for Mid-Infrared Laser

In this work, a series of Tm3+/Ho3+ co-doped tellurite glasses were successfully prepared by the melt-quenching method. The spectroscopic properties around 2 μm of Tm3+/Ho3+ co-doped tellurite glasses were studied under 808 nm laser excitation. Based on the Judd-Ofelt theory, the phenomenological intensity parameters Ω t (t = 2, 4, 6) of the Tm3+/Ho3+ co-doped tellurite glasses were calculated. In addition, the emission cross-section and the gain coefficient of Ho3+ were calculated, and the maximum values are 0.76 × 10−20 cm−1 and 1.38 cm−1, respectively. These results portend that the Tm3+/Ho3+ co-doped tellurite glass has excellent spectroscopic properties and attractive laser performance in mid-infrared waveband.

Ce3+ induced broadband enhancement around 2 μm in Tm3+/Ho3+ co-doped tellurite glass

Tellurite glasses doped with Tm3+, Ho3+ and Ce3+ ions were prepared via melt-quenching to realise broadband and fluorescence enhancement in near-infrared (NIR) band. Under the pumping of a commercial 808 nm laser diode (LD), the emission bands at 2.0 μm, 1.85 μm, 1.47 μm, and 705 nm were observed in the Tm3+/Ho3+ co-doping glass samples, which originated from the transitions of Ho3+:5I7→5I8 and Tm3+:3F4→3H6, 3H4→3F4, 3F2,3 → 3H6, respectively. The existence of 2.0 μm band fluorescence is due to the energy transfer from the Tm3+:3F4 level to the Ho3+:5I7 level. This band overlaps with the 1.85 μm band which forms a broadband fluorescence spectrum in the range of 1600–2200 nm. In glass samples co-doped with Tm3+/Ho3+ with 0.085 mol% Ho2O3 and 1 mol% Tm2O3, the full width at half maximum (FWHM) of this broadband spectrum (1600–2200 nm) was as high as ∼370 nm. After introducing 0.6 mol% CeO2, the emission intensity of broadband fluorescence increased by ∼50%, which was caused by the cross-relaxations between Ce3+ and Tm3+ ions. The lifetime of fluorescence decay was determined to prove the interactions among the doped rare-earth ions, the radiative parameters such as transition probability, branching ratio and radiative lifetime were calculated from the absorption spectra based on the Judd-Ofelt theory to better understand the observed luminescence phenomena. In addition, X-ray diffraction (XRD) confirmed the amorphous state structure of the synthesised glass samples, while Raman spectrum revealed the different vibrational structural units forming the glass network.

Tm3+-doped tellurite fiber weak signal amplifier at a wavelength of 2.27 µm

The amplification of a weak narrow-spectrum pulsed signal at a wavelength of 2.27 µm in Tm3+-doped tellurite fiber was demonstrated. The double-clad Tm3+-doped TeO2–ZnO–La2O3–Na2O glass fiber was used as an amplifier active medium. The pulsed seed signal was selected from the supercontinuum by the high reflective fiber Bragg grating. The experimental setup allowed us to obtain pure amplification data over 2.2 µm without amplified spontaneous emission and nonlinear effects contribution. The gain coefficient of Tm3+-doped tellurite fiber was estimated as 0.11 m−1.

Tm3+-doped fluorotellurite glass microsphere resonator laser at 2.3 µm.

In this Letter, we report lasing at 2.3 µm in Tm3+-single-doped and Tm3+/Ho3+-codoped fluorotellurite glass microsphere resonators. By employing a 793 nm diode laser as a pump and exploiting whispering gallery mode microresonators (WGMRs), dual-wavelength lasing at 1.9 and 2.3 µm and triple-wavelength lasing at 1.9, 2.07, and 2.3 µm are achieved in Tm3+-doped and Tm3+/Ho3+-codoped microspheres, respectively. The introduction of Ho3+ ions significantly reduces the lasing threshold of Tm3+ at 2.3 µm because of energy transfer.

Enhancement of 1.8 μm emission in Er3+/Tm3+ co-doped tellurite glasses: Role of energy transfer and dual wavelength pumping schemes

Thulium (Tm3+) and erbium (Er3+)-doped tellurite glasses were synthesized and explored their spectroscopic properties for optical amplification and medical appliances. The emission at 1.8 μm of Tm3+ ions has been enhanced significantly in Er3+/Tm3+ co-doped tellurite glasses under dual pumping lasers at 808 and 980 nm. Emission cross-section of the Tm3+ ions is found to be 3.46 × 10−20 cm2 which was evaluated by utilizing the Mc-Cumber theory. The possible energy transfer mechanisms between Er3+ and Tm3+ ions under 808 and 980 nm excitations were investigated by utilizing the excitation, emission and decay curve analyses. Effect of dual wavelength pumping on the 1.5 and 1.8 μm spectral profiles is also enlightened. Decay curves of Tm3+:3H4 → 3F4 (1440 nm) transition and Er3+: 4I13/2 → 4I15/2 (1531 nm) transition in the Tm3+ singly and Er3+/Tm3+ co-doped tellurite glasses have been analyzed under 808 nm laser excitation. Energy transfer efficiency is evaluated between Er3+: 4I13/2 and Tm3+:3F4 states from the decay curves and it is found to be 83%. The results are significant and indicating that the Er3+/Tm3+ co-doped tellurite glasses could be a potential candidate for optical fiber amplification at around 1.8 μm region under dual wavelength pumping scheme.

11 W continuous-wave laser operation at 209 μm in Tm:Lu16Sc04O3mixed sesquioxide ceramics pumped by a 796 nm laser diode

High quality thulium doped Lu1.6Sc0.4O3 mixed sesquioxide laser ceramics were fabricated using a solid-state reactive sintering method. Optical and spectroscopic properties of the ceramics were studied. A high transmittance almost identical to the theoretical value of the ceramics was reached at the lasing wavelength. A large Stark splitting of 920 cm−1 for the ground states 3H6 and 472 cm−1 for the first excited states 3F4 of Tm3+ were observed, resulting in a long wavelength emission band around 2.09 μm with low reabsorption losses at this wavelength. CW laser operation at 2.09 μm pumped by a 796 nm laser diode was achieved with an output power of 11 W and an optical-to-optical conversion efficiency of 28.9%, both of which are the highest values reported so far for lasing around 2.1 μm in Tm3+ doped mixed sesquioxide ceramics.

Optically pumped rare-earth-doped Al2O3 distributed-feedback lasers on silicon [Invited

This paper reviews recent progress in the field of optically pumped rare-earth-doped channel waveguide lasers, with a focus on operation utilizing distributed-feedback resonators on silicon wafers. Rare-earth-doped amorphous aluminum oxide thin films have been deposited onto silicon wafers by RF reactive co-sputtering from metallic Al and rare-earth targets, the spectroscopy and optical gain of Er3+, Yb3+, Nd3+, and Tm3+ ions has been investigated, and the near-infrared laser transitions near 1 μm in Yb3+, 1.5 μm in Er3+, and 2 μm in Tm3+ and Ho3+ have been demonstrated. Output power between a few μW and hundreds of mW have been achieved in different waveguide geometries, and ultranarrow-linewidth laser operation has been demonstrated.

Mid-infrared fluorescence properties, structure and energy transfer around 2 µm in Tm3+/Ho3+ co-doped tellurite glass

Tm3+/Ho3+ doped tellurite glasses with good thermal stability and low phonon energy are prepared. 1.8µm fluorescence, enhanced near 2µm fluorescence and a weak 2.3µm fluorescence are observed in the Tm3+/Ho3+ co-doped glasses. The energy transfer mechanism between Tm3+ and Ho3+ has been analyzed according to the absorption spectra, the emission spectra and the level structures of Tm3+ and Ho3+ ions. The decay lifetime of 1.8µm and 2µm fluorescence in Tm3+/Ho3+ co-doped tellurite glass are 0.38ms and 2.46ms, respectively. Moreover, the energy transfer efficiency between Tm3+:3F4 and Ho3+:5I7 levels is calculated and compared. Additionally, the calculated forward energy transfer coefficient CTm-Ho is about five times as large as the reverse energy transfer coefficient CHo-Tm. Results demonstrate that the Tm3+/Ho3+ doped tellurite glass has excellent spectroscopic properties and can be an attractive candidate for 2µm laser.

Emission properties of 1.8 and 2.3 μm in Tm3+-doped fluoride glass

In this work a Tm3+-doped fluoride glass with good thermal stability is prepared. Intensive 1.8 and 2.3 μm emissions are obtained when pumped by an 800 nm laser diode. And the 1.48 μm emission is limited because of the much strong radiation around 1.8 μm. On the basis of absorption spectrum, radiative properties are investigated and discussed according to Judd–Ofelt parameters (Ω2, Ω4, Ω6) calculated by Judd–Ofelt theory. Besides, absorption and emission cross-sections of 3 F 4 → 3 H 6 transition are figured out and analyzed by using McCumber and Beer–Lambert theories. The high gain around 1.8 μm was predicted by the large σemiτrad product (29.8 × 10–21 cm2 ms). The results obtained indicate that the Tm3+-doped fluoride glass can be a promising 2.0 μm laser glass material.

Graphene Q-switched Tm:KY(WO4)2 waveguide laser

We report on the first Tm3+-doped double tungstate waveguide laser passively Q-switched by a graphene saturable absorber using a 12.4 µm-thick 3 at.% Tm:KY0.58Gd0.22Lu0.17(WO4)2 epitaxial layer grown on a (0 1 0)-oriented pure KY(WO4)2 substrate. This laser generated 5.8 nJ/195 ns pulses at 1831.8 nm corresponding to a pulse repetition frequency of 1.13 MHz. These are the shortest pulses achieved in passively Q-switched Tm waveguide lasers. The laser slope efficiency was 9% and the Q-switching conversion efficiency reached 45%. Graphene is promising for the generation of ns pulses at ~2 µm in Tm3+-doped double tungstate waveguide lasers operating in the MHz-range.

Energy Transfer and 1.8 µm Emission in Tm³⁺/Yb³⁺ Co-Doped LiYF₄Crystal.

LiYF₄ single crystals co-doped with various Tm³⁺/Yb³⁺ concentrations were grown using the Bridg- man method. The luminescent properties of the crystals were investigated through emission spectra, emission cross section, and decay curves under excitation by 980 nm. Compared with the Tm³⁺ single-doped LiYF₄ crystal, an enhanced emission band from 1600 to 2150 nm was observed upon excitation of a 980 nm laser diode. The energy transfer from Yb³⁺ to Tm³⁺ and the optimum fluo- rescence emission around 1.80 µm of Tm³⁺ ion were investigated. The maximum emission cross section at 1.8 µm was calculated to be 1.48 x 10⁻²⁰ cm² according to the measured absorption spectrum. The high energy transfer efficiency of 86.5% from Yb³⁺ to Tm³⁺ ion demonstrate that the Yb³⁺ ions can efficiently sensitize the Tm³⁺ ions.

Production and characterization of Tm3+/Yb3+ codoped pedestal-type PbO–GeO2 waveguides

This work explores the production and characterization of pedestal-type active waveguides based on PbO–GeO2 (PGO) thin films codoped with Tm3+/Yb3+ rare earth ions. Silicon wafers containing around 1.7 μm of SiO2 thickness were used as substrate, and the pedestal structure was obtained by conventional photolithography and plasma etching in a reactive ion etching reactor. Plasma etching procedures were made in steps to reduce roughness at the laterals and sidewalls of waveguides. Around 0.5 μm of Tm3+/Yb3+ codoped PGO thin film was obtained by radio frequency magnetron sputtering deposition after etching procedures. Results of scanning electron microscopy confirmed the waveguide pedestal profile. Optical propagation losses around 4, 5, and 20 dB/cm were observed at 1050, 633, and 543 nm, respectively, for waveguide width in the 30–100 μm range. Near field profiles at these wavelengths and also at 980 nm are also reported and confirmed the multimode coupling behavior. The present results corroborate the possibility of using Tm3+/Yb3+ codoped PGO thin films as active waveguides for photonic applications.

Spectroscopic properties of 1.8 μm emission in Tm3+ doped bismuth silicate glass

The emission properties around 1.8μm in Tm3+ doped bismuth silicate glass have been investigated. Based on the obtained Raman spectroscopy and differential scanning calorimetry curves, it is found the introduced Bi2O3 can efficiently reduce the phonon energy of silicate glass to 926cm−1. The energy gap between glass transition temperature and onset temperature of crystallization is 169°C. The OH− content maintains lower in glass by bubbling dry O2 during the melting process. The cut-off wavelength in mid-infrared range is as long as 5μm. Bismuth silicate glass has high radiative transition probability of 238.80s−1 corresponding to the Tm3+:3F4→3H6 transition compared with conventional silicate glasses. The strongest emission at 1.8μm with a large full width at half-maximum of 238nm is achieved from this bismuth silicate glass doped with 0.9mol% Tm2O3. Its fluorescence lifetime at 1.8μm is 640μs.

Spectroscopy and efficient laser operation near 1.95μm of Tm3+ in disordered NaLu(WO4)2

Continuous wave and tunable laser operation at room temperature is demonstrated with single crystals of Tm-doped NaLu(WO4)2. Under Ti:sapphire laser pumping and tuning by an intracavity Lyot filter, the Tm3+ emission extended from 1799to2026nm. The maximum output power exceeded 0.5W and the maximum slope efficiency with respect to the absorbed power was above 58%. These good laser properties are related to the locally disordered tetragonal (I4¯) structure of the crystalline host. Using low temperature spectroscopy and energy level simulation methods, the energy levels and spectroscopic properties of Tm3+ have been shown to be compatible with the S4 site symmetry. This allowed the reliable determination of the emission cross sections related to the laser transitions.

∼2 μm Tm3+/Yb3+-doped tellurite fibre laser

We present, for the first time, laser emission in the range 1.910–1.994 μm in Tm3+/Yb3+-doped tellurite fibre when pumped using an Yb3+-doped double-clad silica fibre laser operating at 1.088 μm. With this pump scheme there was strong pump excited state absorption (ESA) which caused upconversion emission at 800 nm and 480 nm due to the Tm3+: 3H4 → 3H6 and Tm3+: 1G4 → 3H6 transitions, respectively. This strong ESA limited the maximum slope efficiency to 10% with respect to absorbed pump power, and the maximum output power to 67 mW. This is however the highest output power which has been achieved in a tellurite fibre laser so far. The lowest observed threshold was 114 mW for a 22 cm long fibre and a 90% reflective output coupler. Further power scaling was limited due to thermal damage at the pump end of the fibre. The optimum fibre length for this arrangement was around 16 cm but lasing was achieved in lengths ranging from <9 to 30 cm. Tellurite glass offers significant advantages over silicate and fluoride glasses which make it a very promising material for compact, medium power, near and mid-IR fibre lasers for range-finding, medical and atmospheric monitoring and sensing applications.

Single polarized Tm3+ laser in Zn-diffused LiNbO3 channel waveguides

In this work, laser operation at 1.76μm in Tm3+:LiNbO3 Zn-diffused channel waveguides is reported. The laser emission is single polarized with the electric field parallel to the optic axis(π-polarization) and operates in continuous-wave regime, at room temperature. The threshold of laser oscillation is in the range of 40mW, the slope efficiency is around 1%, and both magnitudes are dependent on the channel width, in accordance with the mode overlap between the pump and signal modes within the waveguides.

Concentration Dependence of Emission Properties of Tm3+-Doped Tellurite Glasses in Telecommunication Wavelength Region.

Concentration dependence of emission properties and lifetimes of Tm3+ doped tellurite glasses in telecommunication wavelength region were investigated. According to Judd-Ofelt analysis, it was clarified that the quantum efficiency of 1.46μm in Tm3+-doped tellurite glasses was almost equal to that in fluoride glasses, which were used as host materials for Tm3+-doped fiber amplifiers (TDFA). The emission intensity ratio of the 1.80μm band to the 1.46μm band increased with increasing Tm3+ content. Moreover, the lifetimes of the 3H4 level decreased rapidly with increasing Tm3+ content. These results show that tellurite glass is useful as host materials of TDFA and in order to achieve a high quantum efficiency of 1.46μm emission in tellurite glasses, the concentration of Tm3+ should be low so that cross relaxation can be suppressed.

Spectroscopy and cw operation of a 1.85 μm Tm:KY3F10 laser

Room-temperature cw laser operation on the 3F4?3H6 transition at 1.85 μm of Tm3+ ions in a KY3F10 single crystal is reported here for the first time. Using a cw Ti:sapphire laser as a pump source, a threshold absorbed pump power of 120 mW and a laser slope efficiency of 42.5% were achieved by using a 45% transmissive output coupler. Optimization of the activator concentration and crystal length is discussed taking into account self-quenching and pump-absorption efficiencies as well as parasitic and intrinsic reabsorption losses. The emission cross-section at the laser wavelength is determined using different methods, showing that the result of the J–O approach is, in this case, very uncertain.