Continuous-wave Laser Performance Research Articles

Novel Nd3+ doped BZBO multifunctional crystals for continuous-wave laser applications

Nd3+ doped Bi2ZnB2O7 crystals (NdxBi2-xZnB2O7) with varying doping concentrations were grown using the Kyropoulos method. The crystal structure of NdxBi2-xZnB2O7 were evaluated through powder X-ray diffraction. The segregation coefficients of Nd3+ were determined by XRF to be 0.82 and 0.79 for 2 at.% and 5 at.% Nd: BZBO crystals, respectively. The full-width at half-maximum (FWHM) of the 2 at.% and 5 at.% Nd: BZBO crystals were 55.8 and 37.7 arcsec, respectively. The transmission, absorption and fluorescence spectra were measured. Moreover, the continuous-wave (CW) laser performance was investigated for the 2 at.% Nd: BZBO crystals. All the results indicated that the Nd:BZBO crystal chould potentially serve as a laser matrix.

Reduction of thermal effects in a 2.7-µm Er:Y2O3 ceramic laser with annular pumping.

Reduction of thermal effects is a challenging aspect for power scaling of 2.7-µm bulk Er-lasers due to the large quantum defect when pumping at ∼ 0.97 µm. Here, we demonstrate that thermal effects in an Er:Y2O3 ceramic laser can be significantly reduced pumping by an annular beam, thus improving the continuous-wave (CW) laser performance in the 3-µm spectral range. The excitation conditions of the TEM00 mode were determined theoretically by taking into account the propagation characteristics of the annular pump beam. For a comparison, the temperature and stress distributions are at first theoretically studied with three different pump configurations. In the experiment, output power of the Er:Y2O3 ceramic laser improved by ∼ 60% by changing the pump beam from coventional quasi-top-hat to a designed annular one. This work, as a proof-of-principle study, indicates the potential of power scaling of the 2.7-µm bulk Er-lasers pumping with an annular beam.

Diode-pumped SESAM mode-locked Yb:(Y,Gd)AlO3 laser.

We report on the continuous-wave (CW) and mode-locked (ML) laser performance of an Yb3+-doped yttrium-gadolinium orthoaluminate crystal, Yb:(Y,Gd)AlO3. Pumping by a single-transverse-mode fiber-coupled 976 nm InGaAs laser diode, the maximum output power in the CW regime amounted to 429 mW at 1041.8 nm corresponding to a slope efficiency of 51.1% and a continuous wavelength tuning across 84 nm (1011-1095 nm) was achieved. The self-starting ML operation of the Yb:(Y,Gd)AlO3 laser was stabilized by a semiconductor saturable absorber mirror. Soliton pulses as short as 43 fs were generated at 1052.3 nm with an average output power of 103 mW and a pulse repetition rate of ∼70.8 MHz. To the best of our knowledge, our result represents the first report on the passively mode-locked operation of a Yb:(Y,Gd)AlO3 laser, and the shortest pulse duration ever achieved from any Yb3+-doped orthorhombic perovskite aluminate crystals.

Mid-IR tunable CW and passively Q-switched laser operation of Dy-doped fluoride fiber

We report a comprehensive characterization of tunable continuous-wave (CW) and passive Q-switching laser performance of Dy-doped zirconium fluoride fiber emitting around 3 µm. The in-band pumped CW laser operation is investigated for pump wavelengths varying from 2.7 µm to 2.825 µm, for fiber lengths ranging from 0.4 m to 2 m, and for output coupling efficiency from 10% to 50%, leading to a maximum laser slope efficiency of 44% and a tuning range larger than 300 nm. With Findlay-Clay analysis and Rigrod analyses, optimal cavity parameters are retrieved, paving the way for further optimizations in performance. The passively Q-switched laser operation of Dy-doped fluoride fiber is achieved employing a semiconductor saturable absorber mirror for the first time, demonstrating a stable operation with a minimum pulse duration of 580 ns, a highest repetition frequency of 103 kHz and a pulse energy up to 300 nJ.

Spectroscopy and 2.8 μm laser operation of Er3+-doped (Lu, Y, Sc)-mixed garnet crystal

We report on the spectropic and continuous-wave (CW) laser properties of a novel Er 3+ -doped mixed garnet (Er:LuYSGG) crystal. The maximum phonon energy of Er:LuYSGG was measured to be 720 cm −1 , which is lower than that of Er:YSGG crystal. Fluorescence lifetimes of 4 I 11/2 and 4 I 13/2 levels amounts to 2.1 ms and 3.2 ms, indicating a potential capability for mid-infrared laser emission. For the CW laser operation, a maximum output power of 472 mW was achieved at 2797 nm, with a slope efficiency of as high as 24%. • An Er 3+ -doped (Lu, Y, Sc)-mixed garnet crystal that has a long fluorescence lifetime ( 4 I 11/2 : >2 ms) is proposed. • The phonon energy of Er:LuYSGG crystal is further reduced compared with that of Er:YSGG. • CW laser performance of Er:LuYSGG crystal gives a slope efficiency of 24%, confriming the feasibility of further power improvement.

Crystal growth, structural characterization and laser operation of an Yb0.19Y0.34Lu0.12Gd0.35Ca4O(BO3)3 mixed crystal

An Yb0.19Y0.34Lu0.12Gd0.35Ca4O(BO3)3 mixed oxyborate crystal was grown with large size and high optical quality, by using the Czochralski method. Its crystal structure was characterized by X-ray diffraction measurements. The continuous-wave laser performance of the mixed crystal was investigated with X-, Y- and Z-cut crystals in a plano-concave resonator. An output power of 17.0 W was produced with a Y-cut crystal, the optical-to-optical and slope efficiencies being respectively 49.3% and 55.1%.

Anisotropy of the thermal and laser output properties in Yb,Nd:Sc2SiO5 crystal

The anisotropy of thermal property in an Yb,Nd:Sc 2 SiO 5 crystal is investigated from the temperature of 293 to 573 K. Based on the systematical study of thermal expansion, thermal diffusivity, and specific heat, the thermal conductivity in Yb,Nd:Sc 2 SiO 5 crystals orientated at (100), (010), (001), and (406) is calculated to be 3.46, 2.60, 3.35, and 3.68 W/(m·K), respectively. The laser output anisotropy of a continuous-wave (CW) and tunable laser is characterized, accordingly. A maximum output power of 6.09 W is achieved in the Yb,Nd:Sc 2 SiO 5 crystal with (010) direction, corresponding to a slope efficiency of 48.56%. The tuning wavelength range in the Yb,Nd:Sc 2 SiO 5 crystal orientated at (100), (010), and (001) is 68, 67, and 65 nm, separately. The effects of thermal properties on CW laser performance are discussed.

Continuous wave and SnSe2/PdSe2 passively Q-switched Nd:GdNbO4 laser under direct pumping

In this paper, a continuous wave (CW) and two-dimensional (2D) tin diselenide (SnSe2) and palladium diselenide (PdSe2) passively Q-switched Nd:GdNbO4 laser under direct pumping was demonstrated for the first time. The CW laser performance under the pump at 879 nm was compared to that using traditional 808 nm pumping. The 2D SnSe2 and PdSe2 nanosheets were synthesized by chemical vapor deposition (CVD) technique. The optical properties and microstructures of two nanosheets were investigated. In the passively Q-switched operation, the highest repetition rate, narrowest pulse width, maximum pulse energy and peak power of SnSe2/Nd:GdNbO4 laser were 160 kHz, 555 ns, 2.3 μJ and 4.2 W, respectively. And for PdSe2/Nd:GdNbO4 laser, the corresponding values were 143 kHz, 530 ns, 3.7 μJ and 7.0 W, respectively.

Continuous-wave Laser on Er,Yb-Codoped Pentaborate Crystal

We report, for the first time to our knowledge, a diode-pumped continuous-wave microchip Er,Yb:YMgB5O10 laser. The purpose of this work was to study the growth technique, spectroscopic properties and continuous-wave laser performance of Er3+,Yb3+:YMgB5O10 novel crystal. Absorption and luminescence spectra as well as kinetics of luminescence decay were studied. Ytterbium-erbium energy transfer efficiency was determined. The output characteristics (output power, slope efficiency, laser wavelength) of Er3+,Yb3+:YMgB5O10 laser were determined.Two intensive absorption bands with peaks centered at 937 nm and 976 nm were observed in the absorption spectra at the wavelength near 1 μm. The maximum value of absorption cross-section was determined to be 1.5·10–20 cm2 at 976 nm for polarization E//Ng . A number of narrow lines were observed in the absorption spectra in the 1425–1575 nm spectral range (transition 4I15/2 → 4I13/2 of erbium ions). The lifetime of the upper laser level 4I13/2 of Er3+ ions was determined to be 390 ± 20 μs. The ytterbium-erbium energy transfer efficiency for YMgB5O10 crystal with 2 at.% of Er3+ and 11 at.% for Yb3+ was close to 84 %. The maximal continuous-wave output power of 0.2 W with slope efficiency of 8 % regarding to absorbed pump power was realized at the wavelength of 1570 nm. With the improvement of cavity parameters the output laser performance of the Er,Yb:YMgB5O10 crystal can be further enhanced.Taking into account high thermal conductivity of ≈ 6.2 W·m–1·K–1, the Er,Yb:YMgB5O10 crystal can be considered as a good gain medium for 1.5 μm lasers for applications in laser rangefinder and LIDAR systems.

Continuous-wave laser performance of 10 at% Yb:YSAG transparent ceramics

We report on the continuous-wave and tunable laser operation of transparent 10 at% Yb:Y3Sc1.5Al3.5O12 (Yb:YSAG) ceramics, which have a dense and homogenous microstructure after being sintered at 1820 °C for 10 h. The Yb:YSAG ceramics have excellent optical in-line transmittance characteristics. The broad absorption and emission spectra of Yb:YSAG demonstrated that these ceramics are suitable for laser-diode pumping solid-state lasers. For the 2-mm thick ceramic, a continuous-wave output power of 1.79 W at 1031 nm was measured with a slope efficiency of 18.3%, and a smooth tunable spectra ranging from 1021 nm to 1040 nm has been obtained, with a tunable wavelength exceeding approximately 19 nm.

Growth and laser performance of Tm:SrGdGa3O7 crystal

The TmSrGdGa3O7 crystal was grown by the Czochralski (CZ) method. Continuous-wave, Q-switched, and tunable laser performance are demonstrated based on Tm:SrGdGa3O7 crystal for the first time. The maximum continuous-wave output power was 0.49 W under the absorbed pump power of 8.6 W. Using a commercial WS2 as the saturable absorber, the passively Q-switched laser was successfully achieved. The maximum output power of Q-switched reached up to 0.13 W with the repetition rate of 21.4 kHz and the pulse width of 1.1 μs. A tunable laser was obtained with the whole tuning range of 60.8 nm from 1907.0 to 1967.8 nm.

Spectroscopic properties and continuous-wave laser performance of Yb:Gd2SrAl2O7 crystal

In this paper, the crystal growth, spectral properties, and laser performance of 5 at.% Yb doped Gd2SrAl2O7 (Yb:GSAO) crystal were reported. The peak absorption cross-section is 5.22 × 10−20 cm2 at 979 nm and the peak stimulated emission cross section calculated by Füchtbauer-Ladenburg (FL) method is 1.22 × 10−20 cm2 at 1062 nm for the π polarization. Efficient continuous-wave (cw) laser action was demonstrated in the range of 1060.2–1069.5 nm with a c-cut crystal sample end pumped by a 980 nm laser diode, generating a maximum output power of 7.345 W with an optical-to-optical efficiency of 47.5% and a slope efficiency of 53.7%. The results indicate that Yb:GSAO is a good Yb laser material.

High-power dual-polarization laser operation of Yb:LaCa[formula omitted]O(BO[formula omitted])[formula omitted] crystal

The high-power continuous-wave laser performance of the monoclinic Yb:LaCa4O(BO3)3 crystal was investigated for the first time, revealing complex output-coupling-dependent polarization state varying behavior when a Y-cut crystal was utilized. Under a low output coupling of 1%, the laser oscillation was dominated by the E//X polarization component, producing an output power of 11.0 W with an optical conversion efficiency of 62% and a slope efficiency of 67%, with respect to incident pump power. Dual-polarization laser action was realized under an output coupling of 3% over the entire operational region, and a total output power of 10.2 W was generated at 17.7 W of incident pump power with a slope efficiency of 61%, the output power ratio between the E//X and E//Z components was measured to be 1:1.2.

Highly efficient continuous-wave and ReSe2Q-switched ∼3 μm dual-wavelength Er:YAP crystal lasers

We report on continuous-wave (CW) and rhenium diselenide (ReSe2) Q-switched dual-wavelength mid-infrared (MIR) laser performances of Er:YAP crystal in this Letter. Under an absorbed pump power of 5.5 W, a maximum CW Er:YAP laser output power of 1.02 W is obtained, corresponding to a slope efficiency of 25.3%. With multilayer ReSe2 material as a saturable absorber, a stable Q-switched Er:YAP crystal laser with dual-wavelength output of 2.73 and 2.80 μm is realized for the first time, to the best of our knowledge. The nonlinear optical measurements of the multilayer ReSe2 reveal efficient saturable absorption properties around 3 μm showing a modulation depth of 7.5% and a saturation intensity of 14.5 μJ/cm2. The maximum Q-switching output power reaches 526 mW, and the corresponding laser power jitter is around 3% in 1 h. The shortest pulse duration and the highest pulse repetition rate are 202.8 ns and 244.6 kHz, respectively. These results prove that Er:YAP crystal could be a reliable laser crystal for MIR solid-state lasers.

Growth, spectroscopic properties and laser performances of Yb:La0.11Y0.89VO4 and Yb:La0.15Y0.85VO4 crystals

0.45 at. % Yb doped La0.11Y0.89VO4 and La0.15Y0.85VO4 mixed crystals were grown by the Czochralski method, the structures and polarized spectroscopic properties were systematically studied. The fluorescence lifetimes of these two crystals were 355 and 374 μs, respectively. Continuous wave laser performances of the a-cut mixed crystals were demonstrated, with Yb:La0.11Y0.89VO4, a maximum output power of 1.97 W was achieved at the absorbed pump power of 7.58 W. Passive Q-switched laser with MoS2 as saturable absorber was also achieved, and the maximum average output power was 82 mW at a repetition rate of 200 kHz with a slope efficiency of 20%.

1886-nm mode-locked and wavelength tunable Tm-doped CaF2 lasers.

A 3at.% Tm-doped CaF2 crystal was grown successfully and used as a gain medium. A high-efficiency continuous-wave laser and wide tuning performance were demonstrated in this crystal, and passive mode-locking laser operation was realized for the first time, to the best of our knowledge. For continuous-wave operation, the maximum output power was 2.71W with a high slope efficiency of 70.3%. Using a quartz birefringent filter, a continuous tuning range of approximately 190nm was observed in the tuning mode. In addition, a passively mode-locked Tm3+:CaF2 laser emitting at 1886.8nm was achieved with a semiconductor saturable absorber mirror. At an absorbed pump power of 2.65W, a pulse duration with tens of picoseconds was obtained at a pulse repetition rate of 96.35MHz.

Nd3+-doped transparent tellurite ceramics bulk lasers

We report on the laser emission of the polycrystalline ceramic obtained from the full and congruent crystallization of the parent glass 1Nd3+:75TeO2-12.5Bi2O3-12.5Nb2O5 composition. In particular, the current work underlines the importance of carefully controlling the heat treatment in order to solely crystallize the Bi0.8Nb0.8Te2.4O8 cubic phase and consequently avoid the formation of the BiNbTe2O8 orthorhombic phase that would be detrimental for optical purpose. The structure, microstructure and photoluminescence properties of the resulting transparent tellurite ceramics are characterized. The continuous-wave and gain-switching laser performances reveal that the emission remains perfectly single transversal mode in the range of pump powers explored. The maximum output power achieved was ~28.5 mW, for a pump power threshold of ~67 mW, and with associated efficiency and slope efficiency of ~22.5% and ~50%, respectively. These data definitely stand among the best results obtained so far for bulk laser tellurite materials and thus demonstrate the potential of such polycrystalline transparent ceramics as optically active materials. Finally, the laser emission characteristics in pulsed regime, at low and high repetition rates, are also provided: more than 6.5 W of peak power at a repetition rate of 728 kHz can be obtained.

Growth, spectroscopy and continuous-wave laser performance of Nd3+:LiLu0.65Y0.35F4 crystal

A mixed fluoride crystal of LiLu0.65Y0.35F4 doped with Nd3+ ions was grown by the Bridgman–Stockbarger method. Polarized absorption and luminescence spectra as well as luminescence lifetime were measured at room temperature. Emission probabilities, branching ratios and radiative lifetime were studied within the Judd–Ofelt theory and the emission cross section spectra were calculated. Efficient continuous wave laser operation was demonstrated with the crystal. A maximum output power of 7.7 W and slope efficiency of 60% were achieved at 1047 nm for the TEM00 mode.

Continuous-Wave Mid-Infrared Gas Fiber Lasers

Efficient continuous-wave laser emission of acetylene molecules at 3.1 μ m wavelength has been demonstrated in low-loss hollow-core fiber by optically pumping using a fiber-amplified diode laser around 1.53 μ m. In this paper, we report and compare the continuous-wave laser performance of acetylene molecules in the cavity and single-pass configurations. The use of low-loss antiresonant hollow-core fiber makes the single-pass configuration ideal for high-power laser generation and enables over 1.1 W continuous-wave mid-infrared laser output with over 33% slope efficiency relative to the absorbed pump power. The systematic characterization of power-scaling and pump power absorption properties demonstrates that the molecular kinetics inside hollow-core fiber determines the laser performance, and that low fiber attenuation is key to high-efficiency continuous-wave output.

The optimizing of continuous-wave laser performance of a novel Nd:GdYTaO4 mixed crystal

In this paper, the continuous-wave (CW) performance of a novel Nd:GdYTaO4 laser was investigated through optimizing the transmission (T) of output coupler, the length of laser cavity and the pump beam waist radius (ωp). The maximum CW output power of 2.87W with slope efficiency of 39% was achieved when the absorbed pump power was 8.2W.