【摘要】 Er³⁺基于其⁴I_11/2→⁴I_13/2在2.7～3.0μm的特征发射，常作为中红外固态激光器增益介质的激活离子。采用提拉法生长了一系列Er³⁺掺杂的Gd₃Ga₅O₁₂（GGG）和Lu₃Ga₅O₁₂（LuGG）晶体，计算了吸收截面、发射截面以及能级寿命等光谱参数，研究了Er³⁺掺杂浓度、Pr³⁺共掺对Er:GGG晶体中红外波段荧光发射的影响。对生长的晶体进行了激光实验，采用氙灯泵浦Er/Pr:GGG晶体实现了平均功率为297 mW的2.75μm中红外脉冲激光输出，通过965 nm的半导体LD激光泵浦Er:GGG、GGG/Er:GGG以及Er/Pr:GGG晶体分别实现了最大输出功率为325、453 m W以及372 mW的中红外连续激光输出。最后，采用石墨烯和Bi₂Te₃二维材料作为可饱和吸收体，对GGG/Er, Pr:GGG/GGG键合晶体和Er:LuGG晶体实现的中红外激光进行了调Q实验（激光调谐品质因数实验），实现了最大平均输出功率分别为186 mW和274 m W的中红外脉冲激光，最短脉冲宽度为243 ns。更多还原

【Abstract】 Introduction Mid-infrared（MIR） lasers operating within a spectral region of 2.7–3.0 μm have a significant importance in applications such as laser surgery and remote sensing. Trivalent erbium（Er³） ions are among the most efficient activators for MIR lasers, leveraging the ⁴I_11/2→⁴I_13/2 transition. Nevertheless, the realization of high-power and efficient laser output is often hindered due to the self-terminating effect and substantial thermal loading in Er³⁺-doped gain medium. This study was to investigate the high-performance Er³⁺-doped Gd₃Ga₅O₁₂（GGG） and Lu₃Ga₅O₁₂（LuGG） laser crystals with the low phonon energy and high thermal conductivity. Methods High–quality single crystals of Er: GGG, Er/Pr: GGG, and Er: LuGG were grown by the Czochralski method in an optimized atmosphere（i.e., 98% N₂ + 2% O₂） with iridium crucibles and（111）-oriented seeds. Raw materials underwent multi-step sintering to guarantee the phase purity. Comprehensive spectroscopic analysis was conducted on the polished samples. The room-temperature absorption spectra were determined by a model Lambda 900 spectrophotometer. The fluorescence spectra at the mid-infrared（MIR: 2500–3000 nm）, near–infrared（NIR: 950–1750 nm） and upconversion（UC: 500–700 nm） bands were measured under 965/967 nm excitation by an optical parametric oscillator（OPO） or a xenon lamp using models FLS920 and FSP920 fluorescence spectrometers. The fluorescence decay curves for the ⁴I_11/2 and ⁴I_13/2 energy levels were recorded to determine the fluorescence lifetime. The laser performance was assessed under two pumping schemes（i.e., a xenon lamp and a 965 nm fiber-coupled laser diode（LD））. The crystals were fabricated into laser gain media of various sizes and doping profiles, including a bonded configuration（undoped GGG/56% Er: GGG） to alleviate thermal lensing. The continuous-wave（CW） performance was evaluated via input–output power curves, slope efficiency, laser threshold, and beam quality factor（M²）. The passive Q-switching was implemented with two-dimensional materials（i.e., graphene and a Bi₂Te₃/graphene heterostructure） as saturable absorbers. The main pulsed laser metrics（i.e., pulse train profile, average output power, pulse width, repetition rate, and peak power） were systematically determined. Results and Discussion The as-grown crystals display a high optical quality with intense and broad absorption bands centered at 965 nm. The 30% Er, 0.5% Pr: GGG composition has a notably high absorption cross-section of 5.13×10^–21 cm² and a full width at half maximum（FWHM） of 15 nm, indicating a superior spectral overlap with commercial 980 nm InGaAs laser diodes and enabling efficient pump coupling. The incorporation of Pr³⁺ ions can enhance the MIR fluorescence emission based on a cross-relaxation energy transfer mechanism, i.e., ⁴I_13/2(Er³⁺) + ³H₄(Pr³⁺) → ⁴I_15/2(Er³⁺) + ³F₄(Pr³⁺). This process effectively depopulates the lower laser level(⁴I_13/2), leading to a reversal of the intrinsic lifetime ratio between metastable states. Specifically, a ratio of τ(⁴I_11/2)/τ(⁴I_13/2) of 2.348 appears in the sample 30% Er, 0.5% Pr:GGG, which is critical for overcoming the self–termination barrier in Er³-based ～3 μm lasers. Under 965 nm LD pumping, a CW laser emission at 2.75 μm is attained. The 56% Er: GGG crystal has a maximum output power of 325 m W with a slope efficiency of 16.15%. The bonded GGG/56% Er: GGG structure improves the thermal management, increasing the maximum power to 453 mW and the slope efficiency to 17.1%, while also improving beam quality（i.e., M² reduces from 1.68 to 1.48）. The Er/Pr: GGG crystal（11% Er, 0.4% Pr） shows a superior thermal performance, reaching 372 mW output and a higher damage threshold, due to the lower Er³⁺ concentration and efficient energy transfer. The passive Q-switching with graphene and Bi₂Te₃/graphene absorbers produce impressive pulsed outcomes. The graphene-based Q-switched bonded GGG/Er, Pr: GGG/GGG crystal has a maximum average power of 186 m W, a pulse width of 360 ns, and a repetition rate of 120.5 kHz, corresponding to a pulse energy of 1.54 μJ and a peak power exceeding 4.28 W. The Bi₂Te₃/graphene Q-switched Er: LuGG laser can deliver a higher average power of 274 mW with a shorter pulse width of 340 ns at 135 kHz, yielding a pulse energy of 2.03 μJ and a peak power of > 5.97 W. These findings affirm a potential of these materials in high-performance pulsed MIR lasers. Conclusions This work established Er³⁺-doped GGG and LuGG crystals as highly promising gain media for efficient ～2.75 μm mid-infrared lasers. The strategies of Pr³⁺ co-doping and crystal bonding proved effective in mitigating the self-terminating effect and thermal load, leading to the improvement of substantial performance. The effective operation in both continuous–wave and passively Q-switched regimes could underscore the applicability of these crystals in practical high-power MIR laser systems.更多还原