Μm In Ho3 Research Articles

Wavelength extension beyond 3 µm in a Ho3+/Pr3+ co-doped AlF3-based fiber laser.

In this Letter, we report continuous-wave (CW) lasers with wavelengths beyond 3 µm in homemade Ho3+/Pr3+ co-doped AlF3-based glass fibers. The laser cavity was established through the integration of a dichroic mirror (DM, HR@3-3.1 µm) positioned at the pump end and a partial reflectivity (PR) fiber Bragg grating (FBG) situated at the laser emission end. The FBGs in AlF3-based glass fibers were fabricated by a fs laser direct-writing method, and the resonant wavelengths were 3.009, 3.036, and 3.064 µm, respectively. Under the pump of 1.15 µm laser, a maximum unsaturated output power of 1.014 W was obtained at 3.009 µm with an overall laser efficiency of 11.8% and FWHM bandwidth of 0.88 nm. Furthermore, in order to enhance the optical-thermal stability, the FBG was heat-treated at 200°C for 30 min, and a higher output power of 1081 mW (348 mW without heat treatment) at 3.036 µm was achieved. To the best of our knowledge, this is the first demonstration of 3-3.1 µm lasers by using FBGs in Ho3+/Pr3+ co-doped AlF3-based fibers.

Efficient laser emission at 1191 nm based on Ho3+-doped fluoroaluminate glass in a compact fiber configuration

Efficient laser emission at a wavelength of approximately 1.2 μm in Ho3+-doped AlF3-based glass fiber is reported for the first time. Lasing was achieved through in-band pumping at 1150 nm. The laser cavity's front-end feedback was facilitated by a (High reflectivity, HR) HR-FBG written in Corning HI1060 fiber, spliced to one end of the Ho3+-doped AlF3-based fiber. Fresnel's reflection of the gain fiber provided the other end feedback. The laser performance was characterized by different fiber lengths, and a 31 cm-long fiber achieved a maximum slope efficiency of 70.5 % and a maximum output power of 8.3 W. Furthermore, a series of (Low reflectivity, LR) LR-FBGs written in HI1060 fiber with different reflectivity values were used to replace the Fresnel reflection at the emission end of the gain fiber. The maximum slope efficiency was found to be 54.2 % for a LR-FBG with a reflectivity of 10 %. These results confirm that AlF3-based fiber can potentially serve as gain fiber for higher-power fiber lasers.

Laser operation at 1.2 µm in Ho3+-doped ZBYA glass fibers.

Powerful 1.2-µm laser operation was produced in Ho3+-doped single-cladding, in-house fabricated ZrF4-BaF2-YF3-AlF3 (ZBYA) glass fibers. The fibers were fabricated based on ZBYA glass with a composition of ZrF4-BaF2-YF3-AlF3. Pumped by an 1150-nm Raman fiber laser, the maximum combined laser output power emitted from both sides of a 0.5-mol% Ho3+-doped ZBYA fiber was 6.7 W, with a slope efficiency of 40.5%. We also observed lasing at 2.9 µm with an output power of 350 mW, which was ascribed to the transition of Ho3+:5I6 → 5I7. The effect of rare earth (RE) doping concentration and the length of the gain fiber were also investigated to determine their effect on laser performance at 1.2 µm and 2.9 µm.

Intense mid-infrared emission at 3.9 µm in Ho3+-doped ZBYA glasses for potential use as a fiber laser.

Intense mid-infrared emission at 3.9 µm in Ho3+-doped ZBYA glasses with direct upper laser level (Ho3+:5I5) pumping at a wavelength of 888 nm is reported for the first time, to the best of our knowledge. Spectroscopic parameters were determined using the Judd-Ofelt theory and the measured absorption spectrum. The maximum emission cross section of the Ho3+-doped ZBYA glass is estimated to be 2.7×10-21cm2 at 3906 nm. Additionally, fluorescence spectra and lifetimes of ZBYA glasses with different Ho3+ ion doping concentrations were measured. The results provide theoretical and experimental basis for better selection of rare-earth-doped matrix glasses to achieve a fluorescence output centered on a wavelength of 3.9 µm.

Enhanced mid-infrared emissions of Ho3+/Er3+ co-doped Na5Y9F32 single crystal by introduction of Pr3+ ions

The Na5Y9F32 fluoride single crystals tri-doped with ∼1 mol% Ho3+/∼1 mol% Er3+, and various concentrations of Pr3+ (0, 0.5, 0.8 and 1.0 mol%) were successfully grown by a modified Bridgman method. The absorption, Raman, emission spectra and fluorescence decay curves of Pr3+/Ho3+/Er3+ tri-doped Na5Y9F32 single crystals were studied systematically. The intensity parameters (Ω2 = 1.96 × 10−20 cm2, Ω4 = 1.66 × 10−20 cm2, Ω6 = 1.46 × 10−20 cm2) of Er3+ ions and emission cross-sections at ∼2.7 μm (1.76×10−20 cm2) and ∼2.9 μm (1.34×10−20 cm2) were calculated according to the measured absorption spectra. The emission intensities at ∼2.7 μm of Er3+: 4I11/2 → 4I13/2 and ∼2.9 μm of Ho3+: 5I6→5I7 were enhanced gradually as increase of Pr3+ concentrations from 0 to 1.0 mol% under excitation of 800 nm laser diode (LD). However, the ∼2.0 μm of Ho3+: 5I7→5I8 and ∼1.5 μm of Er3+: 4I13/2 → 4I15/2 were gradually reduced. The introduction of Pr3+ can greatly reduce the lifetimes of Er3+: 4I13/2 and Ho3+: 5I7. The energy transfer from Er3+: 4I13/2 to Ho3+: 5I7 level and depopulating Er3+: 4I13/2 and Ho3+: 5I7 levels under the action of Pr3+ ions are responsible for the enhancement of ∼2.7 and ∼2.9 μm emissions. The Pr3+/Ho3+/Er3+ tri-doped Na5Y9F32 single crystal may become a new choice for ∼3.0 μm mid-infrared solid-state laser.

Enhanced ~2.9 μm mid-infrared emissions of Ho3+/Yb3+ co-doped Na5Y9F32 single crystal introduced by Pr3+ ions

A novel Na5Y9F32 single crystals tri-doped with fixed ~0.8 mol% Ho3+, ~1 mol% Yb3+ and various Pr3+ from 0 to 0.8 mol% were successfully grown by a modified Bridgman method for 2.9 μm mid-infrared application. The effects of Pr3+ ion on the 2.9 μm emission was investigated systematically with the help of the absorption spectra, emission spectra and fluorescence decay curves. The emission intensity at ~2.9 μm of Ho3+: 5I6 → 5I7 was enhanced gradually as increase of Pr3+ concentration from 0 to 0.8 mol% under excitation of 980 nm laser diode (LD). The maximum emission cross-section at ~2.9 μm was calculated to be 5.62 × 10−20 cm2 according to the measured emission spectra. The energy transfer mechanism among Ho3+, Yb3+ and Pr3+ was studied. When the Pr3+ ion concentration reached 0.8 mol%, the energy conversion efficiencies for Ho3+: 5I7 → Pr3+: 3F2 and Ho3+: 5I6 → Pr3+: 3F4 were estimated about ~51.76% and ~15.73%, respectively. A remarkably augmented conversion process of Ho3+: 5I7 → Pr3+: 3F2 by the introduction of Pr3+ ion into Ho3+/Yb3+ system results into the enhancement of ~2.9 μm emission. The Pr3+ ion takes as an effective deactivation of the Ho3+ ion in the Na5Y9F32 single crystal. The Pr3+/Ho3+/Yb3+ tri-doped Na5Y9F32 single crystals may become a new choice for ~2.9 μm mid-infrared solid-state laser due to its both excellent optical properties and chemical stability.

Enhancement mechanisms of Tm3+-codoping on 2 μm emission in Ho3+ doped fluoroindate glasses under 888 nm laser excitation

Ho3+ doped and Ho3+/Tm3+ co-doped fluoroindate glass samples were prepared and their emission properties were compared. Under 888 nm laser excitation, the emission at 2 μm of Ho3+ ions with co-doping 2 mol% Tm3+ ions had a 2.9-fold improvement compared with that of Ho3+ doped. The absorption and emission spectra, and energy level lifetime of Ho3+/Tm3+ co-doped glass samples were measured to analyze the energy transfer processes and enhancement mechanisms. The luminescence intensity at 2 μm can be greatly increased due to the bidirectional energy transfer between Tm3+ and Ho3+ ions.

Enhanced emission at 2.85 μm of Ho3+/Pr3+ co-doped α-NaYF4 single crystal

The Ho3+/Pr3+ co-doped NaYF4 single crystals with various Pr3+ concentrations and constant Ho3+ molar percentage of ~1% were grown by an improved Bridgman method. Compared with the Ho3+ single-doped NaYF4 crystal, an obviously enhanced emission band at 2.85 μm is observed under 640 nm excitation. The Judd-Ofelt strength parameters (Ω2, Ω4 and Ω6) are calculated, the radiative transition probabilities (A), the fluorescence branching ratios (β) and the radiative lifetime (τrad) are obtained in the meantime. The energy transfer from Pr3+ to Ho3+ and the optimum fluorescence emission of Ho3+ ions around 2.85 μm are investigated. Moreover, the maximum emission cross section of above samples at 2.85 μm is calculated to be 0.72×10-20 cm2 for the NaYF4 single crystal with Ho3+ molar percentage of 1% and Pr3+ molar percentage of 0.5% according to the measured absorption spectrum. All results suggest that the Ho3+/Pr3+ co-doped NaYF4 single crystal may have potential applications in mid-infrared lasers.

Energy transfer and 2.0 μm emission in Tm3+/Ho3+ co-doped α-NaYF4 single crystals

Cubic NaYF4 single crystals co-doped with ∼1.90mol% Tm3+ and various Ho3+ concentrations were grown by Bridgman method. The energy transfer from Tm3+ to Ho3+ and the optimum fluorescence emission around 2.04μm of Ho3+ ion were investigated based on the measured absorption spectra, emission spectra, emission cross section and decay curves under excitation of 800nm LD. The emission intensity at 2.04μm increased with the increase of Ho3+ concentration from 0.96mol% to 3.89mol% when the concentration of Tm3+ was held constantly at ∼1.90mol%. Moreover, the maximum emission cross section reached 1.06×10−20cm2 and the maximum fluorescence lifetime was 23.23ms for Tm3+(1.90mol%)/Ho3+(3.89mol%) co-doped one. According to the measured lifetime of Tm3+ single-doped and Tm3+/Ho3+ co-doped samples, the maximum energy transfer efficiency of Tm3+:3F4 level was 95.0%. Analysis on the fluorescence dynamics indicated that electric dipole–dipole is dominant for the energy transfer from Tm3+ to Ho3+.

Broadband mid-infrared 2.8 μm emission in Ho3+/Yb3+-codoped germanate glasses

This work reports the mid-infrared emission properties around 2.85μm in Ho3+/Yb3+ codoped germanate glasses. The glass not only possesses considerably low OH− absorption coefficient (0.24cm−1), but also exhibits low phonon energy (790cm−1). A large spontaneous transition probability (36.66s−1) corresponding to the Ho3+:5I6→5I7 transition has been calculated based on the Judd–Ofelt theory. Besides, a broad 2.85μm fluorescence has been successfully observed and a reasonably model has been proposed to unravel the origin of the broadening emission band. Moreover, the peak emission cross sections of the glass is as high as 9.2×10−21cm2, and the maximum gain per unit length at 2.85μm could be as high as 4.3dB/cm. Results indicate that the prepared germanate glass is a promising candidate for 2.85μm mid-infrared laser materials applications.

Highly efficient mid-infrared 2 μm emission in Ho^3+/Yb^3+-codoped germanate glass

This work reports the mid-infrared emission properties around 2 μm in Ho3+/Yb3+ codoped germanate glasses. The glass not only possesses good chemical durability and good thermal stability but also has high mid-infrared transmittance around 2 μm (90%). In addition, the glass possesses considerably low OH− content (20.45 ppm) and large spontaneous transition probability (103.38 s−1) corresponding to the Ho3+:5I7→5I8 transition. Moreover, the measured lifetime of Ho3+:5I7 level is as high as 7.68 ms, and the quantum efficiency at 2 μm can reach 79.4%. The energy transfer processes of Yb3+:2F5/2 level and Ho3+:5I6 level were quantitatively analyzed according to the rate equation. Results indicate that the prepared germanate glass is a promising candidate for 2 μm mid-infrared laser materials applications.

2.0-μm emission and energy transfer of Ho3+/Yb3+ co-doped LiYF4 single crystal excited by 980 nm**Project supported by the National Natural Science Foundation of China (Grant Nos. 51472125 and 51272109) and the K.C. Wong Magna Fund in Ningbo University, China (Grant No. NBUWC001).

Ho3+/Yb3+ co-doped LiYF4 single crystals with various Yb3+ concentrations and ∼ 0.98 mol% Ho3+ concentration are grown by the Bridgman method under the conditions of taking LiF and YF3 as raw materials and a temperature gradient (40 °C/cm–50 °C/cm) for the solid–liquid interface. The luminescent performances of the crystals are investigated through emission spectra, infrared transmittance spectrum, emission cross section, and decay curves under excitation by 980 nm. Compared with the Ho3+ single-doped LiYF4 crystal, the Ho3+/Yb3+ co-doped LiYF4 single crystal has an obviously enhanced emission band from 1850 nm to 2150 nm observed when excited by a 980-nm diode laser. The energy transfer from Yb3+ to Ho3+ and the optimum fluorescence emission around 2.0 μm of Ho3+ ions are investigated. The maximum emission cross section of the above sample at 2.0 μm is calculated to be 1.08×10−20 cm2 for the LiYF4 single crystal of 1-mol% Ho3+ and 6-mol% Yb3+ according to the measured absorption spectrum. The high energy transfer efficiency of 88.9% from Yb3+ to Ho3+ ion in the sample co-doped by Ho3+ (1 mol%) and Yb3+ (8 mol%) demonstrates that the Yb3+ ions can efficiently sensitize the Ho3+ ions.

Judd–Ofelt analysis, frequency upconversion, and infrared photoluminescence of Ho3+-doped and Ho3+/Yb3+-codoped lead bismuth gallate oxide glasses

Ho 3 + -doped and Ho3+/Yb3+-codoped lead bismuth gallate (PBG) oxide glasses were prepared and their spectroscopic properties were investigated. The derived Judd–Ofelt intensity parameters (Ω2=6.81×10−20 cm2, Ω4=2.31×10−20 cm2, and Ω6=0.67×10−20 cm2) indicate a higher asymmetry and stronger covalent environment for Ho3+ sites in PBG glass compared with those in tellurite, fluoride (ZBLAN), and some other lead-contained glasses. Intense frequency upconversion emissions peaking at 547, 662, and 756 nm as well as infrared emissions at 1.20 and 2.05 μm in Ho3+/Yb3+-codoped PBG glass were observed, confirming that energy transfer between Yb3+ and Ho3+ takes place, and a two-phonon-assisted energy transfer from Yb3+ to Ho3+ ions was determined by the calculation using phonon sideband theory. The 1.20 μm emission observed was primarily due to the weak multiphonon deexcitation originated from the small phonon energy of PBG glass (∼535 cm−1). A large product of emission cross-section and measured lifetime (9.93×10−25 cm2 s) was obtained for the 1.20 μm emission and the gain coefficient dependence on wavelength with population inversion rate (P) was performed. The peak emission cross-section for 2.05 μm emission was calculated to be 4.75×10−21 cm2. The relative mechanism of Ho3+-doped and Ho3+/Yb3+-codoped PBG glasses on their spectroscopic properties was also discussed. Our results suggest that Ho3+/Yb3+-doped PBG glasses are a good potential candidate for the frequency upconversion devices and infrared amplifiers/lasers.