Highly efficient 2 μm CW and Q-switched Tm3+:Lu2O3 ceramics lasers in-band pumped by a Raman-shifted erbium fiber laser at 1670 nm

Highly efficient lasing and thermal properties of Tm:Y2O3 and Tm:(Y,Sc)2O3 ceramics

We report on thermal, spectroscopic, and laser properties of transparent 5 at.% Tm³⁺-doped yttria and "mixed" yttria-scandia ceramics fabricated by vacuum sintering at 1750°C using nanoparticles produced by laser ablation. The solid-solution (Tm_0.05Y_0.698Sc_0.252)₂O₃ ceramic features a broadband emission extending up to 2.3 µm (gain bandwidth, 167 nm) and high thermal conductivity of 4.48 W m^-1 K^-1. A Tm:Y₂O₃ ceramic laser generated 812 mW at 2.05 µm with a slope efficiency η of 70.2%. For the Tm:(Y,Sc)₂O₃ ceramic, the output power was 523 mW at 2.09 µm with η = 44.7%. These results represent record-high slope efficiencies for any parent or "mixed" Tm³⁺-doped sesquioxide ceramics.

In-band pumped Tm,Ho:LiYF4 waveguide laser

A 4.5 at.% Tm, 0.5 at.% Ho:LiYF₄ planar waveguide (thickness: 25 μm) grown by Liquid Phase Epitaxy is in-band pumped by a Raman fiber laser at 1679 nm (the ³H₆ → ³F₄ Tm³⁺ transition). A continuous-wave waveguide laser generates a maximum output power of 540 mW at 2051nm with a slope efficiency of 32.6%, a laser threshold of 337 mW and a linear laser polarization (π). This represents the highest output power extracted from any Tm,Ho waveguide laser. No parasitic Tm³⁺ colasing is observed. The waveguide propagation losses are determined to be as low as 0.19 dB/cm.

High-power 1640 nm Er:Y2O3 ceramic laser at room temperature

We report on the high-power operation of an Er:Y₂O₃ ceramic laser at approximately 1.6 µm using a low-scattering-loss, 0.25 at. % Er³⁺-doped ceramic sample fabricated in-house via a co-precipitation process. The laser is in-band pumped by an Er, Yb fiber laser at 1535.6 nm and generates 10.2 W of continuous-wave (CW) output power at 1640.4 nm with a slope efficiency of 25% with respect to the absorbed pump power. To the best of our knowledge, this is the first demonstration of an approximately 1.6 µm Er:Y₂O₃ laser at room temperature. The prospects for further scaling of the output power and lasing efficiency via low Er³⁺ doping and reduced energy-transfer upconversion are discussed.

Tm3+: Bi4Si3O12 crystal as a promising laser material near 2 μm: growth, spectroscopic properties and laser performance

We report on the crystal growth, spectroscopic properties and laser performance of Tm³⁺-doped Bi₄Si₃O₁₂ (BSO) crystal. The crystal was grown by the vertical Bridgeman method. The spectroscopic properties are investigated based on absorption and luminescence spectroscopy. Judd - Ofelt (JO) analysis is performed to calculate the spontaneous emission probabilities, branching ratio and the radiative lifetimes. The absorption spectrum, emission spectrum and gain cross-section spectra of Tm³⁺: BSO crystal are determined for the 2 μm transition. Luminescence decay kinetic of ³F₄ upper level was analysed in detail. The continuous-wave 2 μm laser with a maximum output power of 650 mW and a slope efficiency of 29.7% is demonstrated for the first time. The beam quality factor (M²) of Tm³⁺: BSO laser was about 1.03 at the maximum output level.

In-band pumping of Tm:LiYF4 channel waveguide: a power scaling strategy for ∼2 μm waveguide lasers

We report on a novel power scaling strategy for thulium waveguide (WG) lasers relying on in-band pumping by high-brightness Raman fiber lasers (RFLs) and the use of liquid-phase-epitaxy-grown fluoride crystalline thin films for better thermal management. Thulium channel WGs are produced by microstructuring the Tm³⁺:LiYF₄/LiYF₄ epitaxies via diamond-saw dicing. They are pumped by a RFL based on an erbium master oscillator power amplifier and a GeO₂-doped silica fiber and emit polarized output at 1679 nm. A CW in-band-pumped (H₆3→F₄3) Tm³⁺:LiYF₄ WG laser generates up to 2.05 W of a linearly polarized single-transverse-mode output at 1881 nm with a slope efficiency of 78.3% and a laser threshold of only 12 mW (versus the absorbed pump power).

High-efficiency high-repetition-rate gain-switched operation around 3 μm in Cr2+:CdSe single-crystal laser pumped by fiber-laser-pumped Ho3+:YAG laser

We report the efficient gain-switched high-repetition-rate Cr²⁺:CdSe single-crystal laser operating around 3 μm and pumped at 2.09 μm by a fiber-laser-pumped Ho³⁺:YAG laser. Average power of up to 6 W with the optical-to-optical efficiency of 67% at 2.65-2.85 μm was achieved in the Cr²⁺:CdSe laser with nanosecond pulses at 8 kHz repetition rate. Wavelength tunability from 2.5 μm to 3.15 μm was demonstrated using a set of cavity mirrors and an intracavity Lyot filter.

Optimization of laser emission at 2.8 μm by Er:Lu2O3 ceramics

We have demonstrated the continuous-wave operation of a highly efficient 2.8 μm Er-doped Lu₂O₃ ceramic laser at room temperature. An Er:Lu₂O₃ ceramic with a doping concentration of 11 at.% afforded a slope efficiency of 29% and an output power of 2.3 W with pumping at 10 W. To our knowledge, these are the highest slope efficiency and output power obtained to date for an Er:Lu₂O₃ ceramic laser at 2.8 μm. In addition, we prepared ceramics with various doping concentrations and determined their emission cross sections by fluorescence lifetime measurements and emission spectroscopy.

Kerr-lens mode-locked Tm3+:Sc2O3 single-crystal laser in-band pumped by an Er:Yb fiber MOPA at 1611 nm

We demonstrate a Kerr-lens mode-locked Tm³⁺:Sc₂O₃ single-crystal laser in-band pumped by an Er³⁺:Yb³⁺ fiber master oscillator power amplifier at 1611 nm. Pulses as short as 166 fs with an average output power of 440 mW are obtained. The spectral bandwidth and center wavelength are 29.3 and 2124 nm, respectively. At a longer pulse duration of 298 fs, we obtain 1 W of average output power. The repetition rate is 95 MHz, and the conversion efficiency against the absorbed pump power is as high as 47%. To the best of our knowledge, this is the first Kerr-lens mode-locked Tm³⁺-doped solid state laser.

Efficient continuous wave and quasi-continuous wave operation of a 2.8 μm Er:Lu2O3 ceramic laser

We have demonstrated a highly efficient 2.8 μm Er-doped Lu₂O₃ ceramic laser and investigated the lasing dynamics by time-resolved spectroscopy. During room-temperature continuous wave operation, a slope efficiency of 22% was achieved with a high-quality transparent ceramic. To our knowledge, this is the highest slope efficiency obtained by an Er:Lu₂O₃ ceramic laser. In addition, an output peak power of 1.2 W was obtained during quasi-continuous wave operation. Time-resolved spectroscopy showed that the emission wavelengths exhibited a red shift from 2715 to 2845 nm, which indicated that continuous wave operation may be possible at 2740 and 2845 nm.