Enhanced 2.7 μm mid-infrared emissions of Er3+ via Pr3+ deactivation and Yb3+ sensitization in LiNbO3 crystal

Cascade Er:YAG pulsed lasers at room temperature

Cascaded mid-infrared (MIR) pulsed laser output in Er:YAG crystals at room temperature is achieved experimentally. The existence of a cascade at room temperature in Er:YAG crystals is confirmed. Furthermore, the effect of the cascade on MIR laser performance is studied. With the assistance of the cascade, the thresholds are reduced by 13.3% and 12.5%, and the slope efficiencies are increased by 3.2% and 12.3% compared to a non-cascade configuration in 10 and 15 at.% Er:YAG, respectively. The excited-state absorption is considered to be the mechanism responsible for the laser performance optimization. This Letter should be helpful for the improvement of erbium-doped 3 µm laser output energy.

Energy Transfer and Cross-Relaxation Induced Efficient 2.78 μm Emission in Er3+/Tm3+: PbF2 mid-Infrared Laser Crystal

An efficient enhancement of 2.78 μm emission from the transition of Er3+: 4I11/2 → 4I13/2 by Tm3+ introduction in the Er/Tm: PbF2 crystal was grown by the Bridgman technique for the first time. The spectroscopic properties, energy transfer mechanism, and first-principles calculations of as-grown crystals were investigated in detail. The co-doped Tm3+ ion can offer an appropriate sensitization and deactivation effect for Er3+ ion at the same time in PbF2 crystal under the pump of conventional 800 nm laser diodes (LDs). With the introduction of Tm3+ ion into the Er3+: PbF2 crystal, the Er/Tm: PbF2 crystal exhibited an enhancing 2.78 μm mid-infrared (MIR) emission. Furthermore, the cyclic energy transfer mechanism that contains several energy transfer processes and cross-relaxation processes was proposed, which would well achieve the population inversion between the Er3+: 4I11/2 and Er3+: 4I13/2 levels. First-principles calculations were performed to find that good performance originates from the uniform distribution of Er3+ and Tm3+ ions in PbF2 crystal. This work will provide an avenue to design MIR laser materials with good performance.

Bulk growth and an efficient mid-IR laser of high-quality Er:YSGG crystals

This work reports on the growth of the high quality large size Er:YSGG crystals and their highly efficient 2.8 nm laser.

High-efficiency 3 μm Er:YGG crystal lasers

By balancing energy transfer and thermal effects, we demonstrate efficient erbium-doped yttrium gallium garnet (Er:YGG) crystal lasers at a wavelength of 2.82-2.92 μm for the first time, to the best of our knowledge. Associated with the influence of doping concentration on energy transfer and thermal effects, the Er³⁺ doping concentration was optimized to be 10 at.%, and with the optimized crystal, the maximum continuous-wave output power was 1.38 W, corresponding to the slope efficiency of 35.4% approaching the theoretical quantum limits. The thermal effects during the laser process were discussed. We believe that this work should be helpful for optimizing the erbium-doped gain for the 3 μm laser and the development of 3 μm lasers.

Temperature-Dependent and Threshold Behavior of Sm3+ Ions on Fluorescence Properties of Lithium Niobate Single Crystals

Temperature-dependent and threshold behavior of Sm3+ ions on fluorescence properties of lithium niobate (LiNbO₃, LN) single crystals were systematically investigated. The test materials, congruent LiNbO₃ single crystals (Sm:LN), with various concentrations of doped Sm3+ ions from 0.2 to 2.0 mol.%, were grown using the Czochralski technique. Absorption spectra were obtained at room temperature, and photoluminescence spectra were measured at various temperatures in the range from 73 K to 423 K. Judd⁻Ofelt theory was applied to calculate the intensity parameters Ωt (t = 2, 4, 6) for 1.0 mol.% Sm3+-doped LiNbO₃, as well as the radiative transition rate, Ar, branching ratio, β, and radiative lifetime, τr, of the fluorescent ⁴G5/2 level. Under 409 nm laser excitation, the photoluminescence spectra of the visible fluorescence of Sm3+ mainly contains 568, 610, and 651 nm emission spectra, corresponding to the energy level transitions of ⁴G5/2→⁶H5/2, ⁴G5/2→⁶H7/2, and ⁴G5/2→⁶H9/2, respectively. The concentration of Sm3+ ions has great impact on the fluorescence intensity. The luminescence intensity of Sm (1.0 mol.%):LN is about ten times as against Sm (0.2 mol.%):LN at 610 nm. The intensity of the fluorescence spectra were found to be highly depend on temperature, as well as the concentration of Sm3+ ions in LiNbO₃ single crystals, as predicted; however, the lifetime changed little with the temperature, indicating that the temperature has little effect on it, in Sm:LN single crystals. Sm:LN single crystals, with orange-red emission spectra, can be used as the active material in new light sources, fluorescent display devices, UV-sensors, and visible lasers.

Efficient 1620 nm continuous-wave laser operation of Czochralski grown Er:Yb:Lu2Si2O7 crystal

Efficient continuous-wave diode-pumped laser operation of Czochralski grown Er:Yb:Lu₂Si₂O₇ crystal is reported. Polarized absorption and emission spectra, fluorescence lifetimes, and energy transfer efficiency from Yb³⁺ to Er³⁺ were determined. A maximal output power of 522 mW was achieved at 1620 nm with slope efficiency of 15.8% and absorbed pump threshold of 470 mW. Among the Er³⁺ and Yb³⁺ co-doped materials with long fluorescence lifetimes of the upper level ⁴I_13/2, which are candidates for gain media of pulsed laser around 1.55 μm with high energy, comprehensive performance of the Er:Yb:Lu₂Si₂O₇ crystal is the best till now.