Large Emission Cross Section Research Articles

Analysis of mid-infrared photoluminescence around 2.85 μm in Yb3+/Ho3+ co-doped synthetic silica-germanate glass

2.85 μm fluorescence of Ho3+ was firstly obtained in Yb3+/Ho3+ co-doped silica-germanate glass. The combination of low OH− concentration and high mid-infrared transmittance were beneficial to the realization of mid-infrared emissions. A large calculated spontaneous radiative transition probability (30.27 s−1) corresponding to the Ho3+:5I6 → 5I7 transition was beneficial for high gain and more opportunity to achieve laser action. Besides, enhanced green (548 nm) and red (662 nm) emissions were obtained due to the energy transfer between Yb3+ and Ho3+. Moreover, the measured lifetime of Ho3+:5I6 reached as high as 283 μs in Yb3+/Ho3+ co-doped silica-germanate glass, which also possesses a large emission cross section (8.05 × 10−21 cm2). All results reveal that Yb3+/Ho3+ co-doped silica-germanate glass might provide a new choice for 2.85 μm laser applications.

Efficient 16 μm linearly-polarized single-frequency phosphate glass fiber laser

Based on the heavily Er3+/Yb3+ co-doped phosphate glass fiber (EYPF) with a larger emission cross-section, an efficient linearly-polarized single-frequency distributed Bragg reflector fiber laser at 1603 nm is demonstrated. By balancing the cavity length against the longitudinal mode spacing, a stable single-longitudinal-mode laser with more than 20 mW is generated from a 16-mm-long EYPF. The measured relative intensity noise of the fiber laser is less than –140 dB/Hz at frequencies of over 5 MHz. The signal-to-noise ratio is greater than 62 dB and the linewidth is less than 1.9 kHz, while the obtained polarization extinction ratio is higher than 25 dB. The L-band operating combined with the narrow linewidth and low noise characteristic makes this laser an ideal candidate for high-resolution molecular spectroscopy and coherent lidar applications.

Broadband ∼3 μm mid-infrared emission in Dy3+/Yb3+ co-doped germanate glasses

The Dy3+/Yb3+ co-doped germanate glasses with good thermal stability have been prepared by the conventional melt quenching method. The J-O intensity parameters and radiative properties such as spontaneous transition probilities (Arad), fluorescence branching ratios (β) and radiative lifetimes (τrad) were investigated according to the absorption spectrum based on Judd-Ofelt theory. An intense emission around ∼3 μm with the FWHM reaching to 322 nm was obtained in present glasses excited by 980 nm LD. The high spontaneous transition probability (63.94 s−1), large emission cross section (6.0 × 10−21 cm2) and superior gain performance corresponding to the Dy3+: 6H13/2 → 6H15/2 transition were obtained. Moreover, the energy transfer mechanism was analyzed qualitatively, and it was found that the energy transfer from Yb3+: 2F5/2 to Dy3+: 6H5/2 level could be quite efficient. Hence, the results indicated that the prepared Dy3+/Yb3+ co-doped germanate glass could be a potential candidate for ∼3 μm mid-infrared solid state lasers.

Exploring the mode-locking laser performance of Yb:LaMgB_5O_10 crystal

The spectral properties of 5 at.% doped Yb:LaMgB5O10 (Yb:LMB) crystal were presented and discussed in detail. The large absorption and emission cross sections, broad emission spectral lines, and considerably good thermal conductivity indicate the considerable potential of Yb:LMB for efficient and powerful ultrashort laser application. In the experiment, the semiconductor saturable absorber mirror (SESAM) mode-locked Yb:LMB laser generated pulses with the pulse duration of 182 fs and the central wavelength of 1025.2 nm. The maximum average power was 2.49 W with the slope efficiency of 48% and the optical to optical efficiency as high as 32%. Furthermore, pulses of 148 fs with average output power of 1.52 W and 108 fs with 0.61 W were obtained based on Yb:LMB crystal. To the best of our knowledge, this is the first demonstration of mode-locked pulse generation from the Yb:LMB laser.

Highly Efficient 2.84- $\mu \text{m}$ Emission in Ho3+/Yb3+ Co-Doped Tellurite–Germanate Glass for Mid-Infrared Laser Materials

The use of Yb 3+ co-doping with Ho 3+ to enhance the Ho 3+ : 5 I 6 → 5 I 7 ~ 2.84-μm emissions is investigated in the tellurite-germanate glasses. An intense ~ 2.84-μm emission with a full width at half maximum (FWHM) of 132 nm is achieved in the Ho 3+ /Yb 3+ co-doped tellurite-germanate glass upon excitation at 980 nm. The glass not only possesses considerably low OH - absorption coefficient (0.206 cm$^{-1}$ ), but also exhibits 2.84-μm large emission cross section (14.6 × 10 -21 ). Moreover, the measured lifetime of Ho 3+ : 5 I 6 level is as high as 0.283 ms. Results reveal that Ho 3+ /Yb 3+ co-doped Tellurite-germanate glass is an attractive host for developing a mid-infrared 3-μm solid-state laser.

Growth and spectroscopic investigations of the 1.5 at.% Er:GSGG laser crystal

The 1.5 at.% Er3+ doped gadolinium scandium gallium garnet (GSGG) laser crystal with high optical quality was successfully grown by the Czochralski method. The structural parameters were obtained by x-ray Rietveld refinement. A high crystalline quality of Er:GSGG was determined by x-ray rocking curve. The spectroscopic parameters of Er3+ ion were calculated and analyzed using the Judd–Ofelt theory. Furthermore, the stimulated-emission cross-section spectra were investigated for the 4I13/2 → 4I15/2 transitions at 1.5–1.6 µm, which indicates the great potential of Er:GSGG for multi-wavelength emission at 1.5–1.6 µm. The larger emission cross-section and long fluorescence lifetimes around 0.55 and 0.67 µm mean that the 1.5 at.% Er:GSGG crystal is beneficial for green and red laser generation. Meanwhile, the intensity of the emission spectra was compared between the 1.5 at.% and 2.0 at.% Er-doped GSGG. The roles of cross-upconversion, cross-relaxation and the excited-state absorption process were discussed in the 1.5 at.% Er:GSGG crystal for generating visible and 1.5–1.6 µm lasers.

Growth, structure and spectroscopic properties of 1 at.% Er3+: GdTaO4 laser crystal

1at% Er3+ doped Er: GdTaO4 laser crystal with high optical quality was successfully grown by the Czochralski method. The structural parameters were obtained by the X-ray Rietveld refinement. A high crystalline quality of Er: GdTaO4 was determined by the X-ray rocking curve. The transition intensity parameters of Er3+ ions were fitted according to the absorption spectra along three principal polarization directions. The relatively larger emission cross section (1.022×10−20cm2), long fluorescence lifetime ( 5.66ms) and relatively weaker reabsorption phenomenon around 1.6µm indicate that 1at% Er: GdTaO4 crystal can be used as a promising NIR laser material. Meanwhile, the stimulated emission cross-section spectra along three principal polarization directions were investigated for 4I13/2 →4I15/2 transitions at 1.5–1.6µm which indicates a great potential of Er: GdTaO4 for multi-wavelength emission at 1.5–1.6µm. In addition, the possibility of generating green and red lasers in Er: GdTaO4 was also analyzed and evaluated.

Intense 2.7 μm emission in Er3 + doped zinc fluoride glass

A novel erbium ion doped zinc fluoride glass was prepared. 2.7μm emission and transmittance properties together with thermal ability were investigated. An enhanced 2.7μm emission was observed by introducing ZnF2 in the ZrF4-based fluoride glass. Meanwhile, the J-O parameters and branching ratios (β) of Er3+-doped zinc fluoride glass were calculated and analyzed. The present Er3+-doped zinc fluoride glass with large emission cross-section (0.92×10−20cm2) and long decay lifetime (2.05ms) at 2.7μm indicates that it have very promising applications for solid state lasers around 3μm.

Silicon-erbium ytterbium silicate nanowire waveguides with optimized optical gain

Single-crystal erbium silicate nanowires have attracted considerable attention because of their high optical gain. In this work, we report the controlled synthesis of silicon-erbium ytterbium silicate core-shell nanowires and fine-tuning the erbium mole fraction in the shell from x = 0:3 to x = 1:0, which corresponds to changing the erbium concentration from 4:8 × 1021 to 1:6 × 1022 cm-3. By controlling and properly optimizing the composition of erbium and ytterbium in the nanowires, we can effectively suppress upconversion photoluminescence while simultaneously enhancing near-infrared emission. The composition-optimized nanowires have very long photoluminescence lifetimes and large emission cross-sections, which contribute to the high optical gain that we observed. We suspended these concentration-optimized nanowires in the air to measure and analyze their propagation loss and optical gain in the near-infrared communication band. Through systematic measurements using wires with different core sizes, we obtained a maximum net gain of 20±8 dB·mm-1, which occurs at a wavelength of 1534 nm, for a nanowire with a diameter of 600 nm and a silicon core diameter of 300 nm.

Effect of alkaline earth oxides on the physical and spectroscopic properties of Dy3+- doped Li2O-B2O3 glasses for white emitting material application

Li2O–MO-B2O3:0.5Dy2O3 glasses mixed with four different alkaline earth modifier oxides MgO, CaO, SrO and BaO were synthesized by melt quench technique. Their physical properties like density, molar volume and refractive index were measured at room temperature and the effect of alkaline earth modifier oxides were studied. Also, optical absorption and photoluminescence spectra of these glasses have been acquired at room temperature. The Judd–Ofelt theory was effectively used to characterize these spectra and spectral intensities (ƒcal), Judd–Ofelt intensity parameters (Ω2, Ω4 and Ω6) and certain radiative properties have been determined. Radiative life-times (τR), branching ratios (βcal), and emission cross-sections (σp) and optical gain parameters (σp × τR) were calculated from the Judd–Ofelt intensity parameters and the variation in these parameters with the variation of glass matrix are discussed. Yellow/Blue (Y/B) ratio and chromacity color coordinates (x,y) are calculated from the emission spectra which indicates the white light generation from all the investigated samples. The correlated color temperature (CCT) for the studied glasses is found to be 4418 K. The fluorescence decay time (τexp) of the 4F9/2 level of Dy3+ has been measured from the decay profiles and compared with calculated lifetimes (τcal). Among all the studied glass matrices, the glass containing BaO exhibits high value of branching ratio, large emission cross-section and high optical gain parameter for 6F9/2 → 6H13 at 575 nm. The results indicates the suitability of all the studied glasses for laser action and white light generation.

2 μm emission properties and nonresonant energy transfer of Er3+ and Ho3+ codoped silicate glasses.

2.0 μm emission properties of Er3+/Ho3+ codoped silicate glasses were investigated pumped by 980 nm LD. Absorption spectra were determined. Intense mid-infrared emissions near 2 μm are observed. The spectral components of the 2 μm fluorescence band were analyzed and an equivalent model of four-level system was proposed to describe broadband 2 μm emission. Low OH− absorption coefficient (0.23 cm−1), high fluorescence lifetime (2.95 ms) and large emission cross section (5.61 × 10−21 cm2) corresponding to Ho3+: 5I7→5I8 transition were obtained from the prepared glass. Additionally, energy transfer efficiency from the Er3+: 4I13/2 to the Ho3+: 5I7 level can reach as high as 85.9% at 0.75 mol% Ho2O3 doping concentration. Energy transfer microscopic parameters (CDA) via the host-assisted spectral overlap function were also calculated to elucidate the observed 2 μm emissions in detail. Moreover, the rate equation model between Er3+ and Ho3+ ions was developed to elucidate 2 μm fluorescence behaviors with the change of Ho3+ concentration. All results reveal that Er3+/Ho3+ codoped silicate glass is a promising material for improving the Ho3+ 2.0 μm fiber laser performance.

Kerr-lens mode-locked Yb3+-doped Lu3Al5O12 ceramic laser.

Yb:LuAG is a promising gain medium for high-power lasers due to its high thermal conductivity and large emission cross section. Although narrowband gain media such as Yb:LuAG are not considered to be suitable for the generation of sub-100 fs pulses, we have achieved generation of 91 fs pulses with Yb:LuAG ceramic by the Kerr-lens mode-locking (KLM) technique. The obtained average power, pulse energy, and peak power were 1.64 W, 20.0 nJ, and 220 kW, respectively. These are, to the best of our knowledge, the first demonstration of KLM and the new records based on both Yb:LuAG ceramic and single crystal.

Efficient high repetition rate electro-optic Q-switched laser with an optically active langasite crystal.

With an optically active langasite (LGS) crystal as the electro-optic Q-switch, we demonstrate an efficient Q-switched laser with a repetition rate of 200 kHz. Based on the theoretical analysis of the interaction between optical activity and electro-optic property, the optical activity of the crystal has no influence on the birefringence during Q-switching if the quarter wave plate used was rotated to align with the polarization direction. With a Nd:LuVO4 crystal possessing a large emission cross-section and a short fluorescence lifetime as the gain medium, a stable LGS Q-switched laser was designed with average output power of 4.39 W, corresponding to a slope efficiency of 29.4% and with a minimum pulse width of 5.1 ns. This work represents the highest repetition rate achieved so far in a LGS Q-switched laser and it can provide a practical Q-switched laser with a tunable high repetition rates for many applications, such as materials processing, laser ranging, medicine, military applications, biomacromolecule materials, remote sensing, etc.

Spectral and Laser Properties of Yb:LuAG Transparent Ceramics Fabricated by Tape Casting Method

Yb3+‐doped LuAG laser ceramics with different Yb3+‐doping concentrations were successfully fabricated by nonaqueous tape casting method and vacuum sintering technology. XRD patterns and SEM morphologies of the ceramics were presented. The optical in‐line transmittance of the Yb‐doped LuAG ceramics was about 83% at 1030 nm. The fluorescence lifetime of annealed and unannealed ceramic samples was compared. From the spectroscopic properties, it can be seen that the ceramics had a large emission cross section of 2.9 × 10−20 cm2 with a FWHM of about 7.2 nm at 1030 nm. Under 100% population inversion, the maximum gain coefficient was estimated to be 12.4 cm−1 at 1030 nm. With a fiber‐coupled diode laser as pump source, CW laser at 1030 nm was demonstrated and the maximum output power of 338.9 mW was achieved with a slop efficiency of 19%. A tuning range from 1028 to 1036 nm was obtained.

Spectroscopic and structural characterization of barium tellurite glass fibers for mid-infrared ultra-broad tunable fiber lasers

To meet the growing demand for mid-infrared tunable fiber lasers, the spectroscopic and structural properties of Tm3+/Ho3+ co-doped barium tellurite glass fibers are systematically evaluated by absorption, Raman, and photoluminescence spectra measurements. The density, molar volume, refractive index, and glass transition temperature are assessed in detail to fully understand their basic physical and thermal properties. Benefitting from the multiple structural sites in a barium tellurite glass system, the maximum doping concentration of Tm2O3 reaches up to 6.0 wt.% without inducing any crystallization or phase separation. Such a high ion concentration is conducive to reducing the fiber length and obtaining an efficient laser output. Furthermore, an intense ~2.0 μm ultra-broad emission with a full width at half maximum (FWHM) of 382 nm is achieved in the Tm3+/Ho3+ co-doped sample upon excitation at 808 nm by properly adjusting Tm3+ concentration and fiber length. The larger emission cross-sections and higher gain coefficients along with excellent thermal stability indicate that this barium tellurite glass could be an attractive gain medium for mid-infrared ultra-broad tunable fiber lasers.

2 μm emission properties and hydroxy groups quenching of Tm3+ in germanate-tellurite glass

Tm3+ activated germanate-tellurite glasses with good thermal stability and anti-crystallization ability were prepared. Efficient 2 μm fluorescence was observed in the optimal concentration Tm3+ doped glass and the corresponding radiative properties were investigated. For Tm3+: 3F4 → 3H6 transition, high spontaneous radiative transition probability (260.75 s−1) and large emission cross section (7.66 × 10−21 cm2) were obtained from the prepared glass. According to Dexter's and Forster's theory, energy transfer microscopic parameters were computed to elucidate the observed 2 μm emissions in detail. Besides, the effect of hydroxy groups quenching was also quantificationally investigated based on simplified rate equations. Results demonstrate that the optimal concentration Tm3+ doped germanate-tellurite glass possessing excellent spectroscopic properties might be an attractive candidate for 2 μm laser or amplifier.

Growth and optical properties of Pr3+:KLu(WO4)2 laser crystal: a candidate for red emission laser

A Pr3+:KLu(WO4)2 crystal with dimension of 30 × 30 × 15 mm3 was grown in the K2W2O7 flux. A slice was cut from the crystal, and the polarized absorption and fluorescence spectra were measured at room temperature. Based on the J-O theory, the oscillator intensity parameters Ω t (t = 2, 4, 6), spontaneous emission probabilities and branch ratios were estimated and good results had been obtained. Furthermore, the crystal has a relatively large emission cross-section in the region of 615–630 nm with the highest value of 14.5 × 10−20 cm2, which indicates that the crystal is good for the application in red emission laser. The emission decay time for 1D2 and 3P0 multiplets was discussed. By adapting the I-H model to fit the emission decay curves, the lifetime for 1D2 at 607 nm and 3P0 at 615 nm are 19.72 μs and 8.95 μs, respectively. Then the corresponding fluorescence quantum efficiencies of the two multiplets reach 83.7 % and 87.9 %, respectively. All the studies illustrate that this crystal is potential in red emission laser application.

Mid-Infrared 2.86-$\mu \text{m}$ Emission Characteristics in Highly Dy3+ Doped Fluoroaluminate Glass

A highly Dy3+ doped (10 mol%) fluoroaluminate glass was successfully fabricated by melt-quenching method for the first time. The intensity of 2.86- $\mu \text{m}$ emission increases with the Dy3+ ions concentration without fluorescence quenching because of the large dispersibility of Dy3+ ions in this glass network without clustering. Radiative and emission parameters were calculated based on the Judd–Ofelt theory, which show that the 10 mol% highly doped sample possesses a high calculated spontaneous transition probability (32.01 $\text{S}^{-1}$ ) together with a large emission cross section ( $5.94 \,\, \times \,\, 10^{-21}$ cm2) of Dy3+: $^{6}\text{H}_{13/2}\to ^{6}\text{H}_{15/2}$ transition. In addition, the increasing $\Omega _{t}$ ( $t=2$ ,4,6) values, which caused by a complex outermost electron configuration of Dy3+ ions, have been further discussed to analyze the partial glass structure.

Intense 2.89 μm emission from Dy³⁺/Yb³⁺-codoped PbF₂ crystal by 970 nm laser diode pumping.

A novel Dy(3+)/Yb(3+) co-doped PbF2 mid-IR laser crystal was successfully grown using the vertical Bridgman method. Efficient emission at around 3 μm from the crystal was observed under excitation of a conventional 970 nm laser diode (LD). The energy transfer efficiency from Yb(3+) to Dy(3+) in Dy(3+)/Yb(3+):PbF2 crystal is as high as (97.7±0.3)%. It is also found that the Dy(3+)/Yb(3+):PbF2 crystal possesses long fluorescence lifetime (15.4±0.2) ms, high quantum efficiency (95.0±0.3)%, and large emission cross section (1.37±0.11)×10(-20) cm2 corresponding to the stimulated emission of Dy(3+):(6)H(13/2)→(6)H(15/2) transition. Additionally, the phonon energy of the crystal was analyzed by the Raman spectrum. These results indicate that Dy(3+)/Yb(3+):PbF2 crystal may become a promising material for 3 μm solid state lasers under a conventional 970 nm LD pump.

Observation of Midinfrared 4-$\mu \text{m}$ Emission in Ho3+-Doped Fluoroaluminate Glasses

Ho3+ activated fluoroaluminate glasses were prepared successfully via melt-quenching method. Not only 2- and 2.85- $\mu \text{m}$ emissions but also 4- $\mu \text{m}$ emissions were observed for the first time by 900-nm Ti: sapphire laser pumping. The optimal midinfrared emissions were obtained when Ho3+ concentration reaches 1 mol%. Spectroscopic properties and energy transfer mechanism of Ho3+ were investigated in detail. Results indicate that the prepared glasses possess high midinfrared transmittance (90%), large emission cross sections at $2~\mu \text{m}$ ( $7.6 \times 10^{-21} $ cm $^{2}$ ), $2.85~\mu \text{m}$ ( $17.6 \times 10^{-21}$ cm $^{2}$ ), and 4 $\mu \text{m}$ ( $6.87 \times 10^{-21}$ cm $^{2}$ ) together with superior gain properties. It is suggested that Ho3+ activated fluoroaluminate glass is an attractive candidate for midinfrared laser materials application.