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We demonstrate the structure, spectroscopy, and laser performance of an Er3+ and Pr3+ co-doped LuYSGG crystal grown by the Cz method. The XRD result shows that it belongs to the cubic system with the space group Ia3¯d. A refractive index curve in the range of 320–3000 nm is obtained by fitting the Sellmeier equation. The lifetimes of the 4I13/2 and 4I11/2 levels are 0.871 and 0.728 ms, and the ratio is reduced obviously from 3.4 to 1.2 due to the doping of deactivator Pr3+. In CW mode, a maximum output power of 1059 mW is achieved with a slope efficiency of 17.58% and laser center wavelength of ∼2.8 μm. Beam quality factors of 1.40/1.34 are achieved. The results suggest that the Er,Pr:LuYSGG crystal is a potential candidate for generating a high-power mid-infrared laser and can be applied in irradiation environments. [ABSTRACT FROM AUTHOR]

• Laser performance of LD side-pumped Er:LuYSGG bonding crystal was demonstrated. • Maximum output power of 20.76 W is achieved and improved effectively by bonding. • M 2 factors of 6.80/6.74 of the bonding crystal are better than that of un-bonding one. • Er:LuYSGG bonding crystal is a promising 2.8 μm gain element operated at high power. We demonstrate the laser performance of 970 nm LD side-pumped LuYSGG/Er:LuYSGG/LuYSGG bonding crystal in a frequency range of 50–800 Hz. The thermal distribution simulation implies that the bonded Er:LuYSGG crystal possesses a higher cooling efficiency compared with the un-bonded one. The maximum average power of 20.76 W is realized at a frequency of 150 Hz and a pulse width of 200 μs, corresponding to a slope efficiency of 23.94 % and optical-to-optical conversion efficiency of 19.22 %. A single laser wavelength of 2797.5 nm is observed. The M 2 factors of the bonding rod are 6.80/6.74, indicating a relatively high beam quality. Therefore, the LuYSGG/Er:LuYSGG/LuYSGG bonding crystal exhibits an improvement of laser performance operated at 2.8 μm due to excellent heat dissipation ability, which is a promising gain element and can be applied to the harsh radiation environment. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate the laser performance of LD end-pumped LuYSGG/Er:LuYSGG composite crystal. Thermal distribution simulations by varying the pump spot size indicate that the suitable pump power density is a key factor affecting the laser performance, which is consistent with the experimental result. The maximum output power and slope efficiency achieved were 1266 mW and 24.3% in CW mode, which increased by 39.3% and 12.5%, respectively, compared with unbonded Er:LuYSGG crystal. The laser wavelength location was at 2797.6 nm, and the power fluctuation was about 5.1%. Moreover, the beam quality factors Mx2 and My2 improved to 1.33 and 1.42 from 1.78 and 1.83, respectively. The results suggested that an LD end-pumped LuYSGG/Er:LuYSGG composite crystal with a high beam quality can be applied as a seed source in the mid-infrared (MIR) multi-stage amplification laser apparatus. [ABSTRACT FROM AUTHOR]

• Influence of 60Co gamma-ray irradiation on the Er:LuYSGG crystal was demonstrated. • Maximum average output power of 886 mW is achieved after irradiation. • Maximum output power and slope efficiency are reduced by only 2.5% and 3.7%. • Lifetime ratio between lower and upper laser levels is reduced after irradiation. • Er:LuYSGG crystal is a potential 2.79 μm radiation-resistant laser material. We demonstrate the influence of gamma-ray irradiation on the structure, spectroscopies, and laser performance of Er:LuYSGG crystal. After 100 Mrad 60Co gamma-ray irradiation, the crystal structure remains unchanged, the absorption near 968 nm and emission within 2.7 ∼ 3 μm are almost unaffected, the level lifetimes are reduced, and the maximum output power of 886 mW is achieved with a maximum slope efficiency of 20.8%. The maximum output power and slope efficiency decrease by only 2.5% and 3.7% after irradiation, respectively, and the M 2 factor is little affected by irradiation. The results indicate that the Er:LuYSGG crystal is a potential mid-infrared radiation-resistant laser material applied in radiation environments. [ABSTRACT FROM AUTHOR]

A novel Yb,Ho,Pr:LuYAG laser crystal was successfully grown and investigated in detail, which belongs to the cubic system with a space group of I a-3d. The X-ray rocking curve of the as-grown crystal implied high crystalline quality. The dislocation defects were revealed by the chemical method. Moreover, the density, thermal expansion coefficient and thermal conductivity were determined. The absorption coefficient at 935 nm and the emission cross-section at 2.911 μm were obtained to be about 15.18 cm−1 and 2.23 × 10−21 cm2, respectively. The lifetime of the lower laser level 5I 7 was shown to decrease from 7.58 to 5.88 ms, while that of the upper laser level 5I 6 basically remained unchanged, suggesting that the co-doped Pr3+ possessed an efficient deactivation effect and was beneficial in attaining population inversions of Ho3+. The corresponding findings illustrate that the Yb,Ho,Pr:LuYAG crystal can serve as a novel promising gain medium for realizing the 2.911 μm laser pumped by ~ 940 nm high-power InGaAs laser diode. • A novel Yb,Ho,Pr:LuYAG laser crystal was successfully grown by Czochralski method. • The crystal possesses a high thermal conductivity, which is helpful in dissipating heat during laser action. • Yb3+ makes the crystal suitable for 935 nm LD pumping and Pr3+ can inhibit self-termination phenomenon. • High absorption coefficient at 935 nm and large emission cross-section at 2911 nm are beneficial in realizing ∼2.9 μm laser. • The Yb,Ho,Pr:LuYAG crystal is a new promising gain medium for realizing 2.911 μm laser. [ABSTRACT FROM AUTHOR]

Yb3+ and Ho3+ co-doped Lu2.55Y0.45Al5O12 (Yb,Ho:LuYAG) crystal with a size of Φ 28 mm × 120 mm was successfully grown by the Czochralski method. The lattice parameters of the as-grown Yb,Ho:LuYAG crystal were obtained by Rietveld refinement with the XRD data. The result of X-ray rocking curve indicated that the grown crystal has a high crystalline quality. From strong absorption band near 935 nm and emission bands within 2700–3000 nm, we found that the Yb3+ ions can be acted as the sensitizer for the activator ions Ho3+. Furthermore, the lifetimes of the 5I6 and 5I7 levels of the Ho3+ ions were 68.25 μs and 7.58 ms, respectively. These results indicated that the Yb,Ho:LuYAG crystal is a promising gain material for 2.91 μm laser pumped by a 940 nm LD. [ABSTRACT FROM AUTHOR]

• Er,Pr:YAP crystals with two different Pr3+ concentrations are grown by CZ method. • Influence of Pr3+ concentrations on the luminescence and laser properties are investigated contrastively. • Watt-level ∼2.7 μm laser is achieved on the Er,0.1Pr:YAP crystal by LD end-pumping. • ∼2.7 μm laser power can be improved by optimizing the concentrations of deactivating Pr3+. High-quality Er,Pr:YAP crystals with two different Pr3+ concentrations are grown successfully, and the spectra and laser performances are studied in contrast. Both two crystals exhibit a wide absorption band with a central wavelength at 972 nm and high transmittance of over 80% in the wavelength range of 2.5 to 5 μm. The luminescence and laser properties are improved when the concentration of Pr3+ decreased from 0.2 at% to 0.1 at%. The maximum powers of 1040 and 835 mW are achieved in the Er,0.1Pr:YAP, and Er,0.2Pr:YAP crystals, corresponding to slope efficiencies of 13.97% and 10.94%, respectively. All the results indicate that co-doping with an appropriate concentration of deactivating Pr3+ is an effective method to attenuate the self-termination effect of Er3+, and then further improve the laser performance. [ABSTRACT FROM AUTHOR]

• High-quality Ho:YAP crystal was fabricated by the Czochralski method. • The structure, spectroscopy and J-O parameters of Ho:YAP were discussed. • For the first time, ∼3 μm CW laser was realized in single Ho-doped crystal host. • Maximum power of 176 mW and slope efficiency of 3.36% was obtained. We demonstrate the spectroscopy and mid-infrared laser performance on the Ho:YAP oxide crystal grown by the Czochralski method in detail. The crystal belongs to orthorhombic system of Pnmb (62) space group and shows high crystalline quality. The lifetimes of 5I 6 and 5I 7 levels are 0.412 and 4.485 ms, respectively. Particularly, under 1150 nm Raman fiber laser pumping, a 3.01 μm CW laser with a maximum power of 181 mW and slope-efficiency of 3.35% is achieved. The M2 factor of 1.35/1.37 indicates that the yield laser has excellent beam quality. The results reveal that the Ho:YAP crystal possesses great potential for developing efficient 3.0 μm mid-infrared lasers. [ABSTRACT FROM AUTHOR]

• Cascade Er:YSGG crystal pulsed lasers near 1.6 and 2.8 μm are realized at room temperature. • The slope efficiency of MIR laser increases to 4.2 % from 1.9 % by cascade process. • Four laser wavelengths of 2.793, 2.821, ∼2.860, 2.917 μm in Er:YSGG laser are discovered. • The cascade process can improve the MIR laser performance based on the Er:YSGG crystal. We demonstrate a pulsed cascade laser on LD end-pumped Er:YSGG crystal near 1.6 and 2.8 μm at room temperature for the first time. The slope efficiency of mid-infrared laser with the assistance of cascade process is significantly improved. Under the working frequency of 100 Hz and pump pulse width of 6 ms, a maximum power of 243 mW centered at 2.79 μm is achieved with increasing slope efficiency of 4.2 %, while the slope efficiency of non-cascade is only 1.9 %. Under high pump power, four laser wavelengths of 2.793, 2.821, ∼2.860, and 2.918 μm are discovered and the phenomenon is explained according to the Boltzmann factors. This work would be conducive to the exploration of pulsed cascade laser based on the Er:YSGG crystal. [ABSTRACT FROM AUTHOR]

We demonstrate the temperature distribution and 2.79 μ m laser performance in a high-quality Er:YSGG single crystal fiber (SCF) with size of Φ 0.85 × 8 mm3 for the first time. Compared with 2 × 2 × 8 mm3 Er:YSGG bulk crystal, the simulation results show that the center maximum temperature of Er:YSGG SCF is much lower, and the temperature rising and total thermal deformation are evidently reduced, indicating that the SCF possesses more efficient thermal dissipation. Under 970 nm laser diode pumping, a maximum output power of 636 mW with slope efficiency of 20.2% is realized. More importantly, a high beam quality factors M x 2 / M y 2 of 1.28/1.29 is obtained, which is close to the fundamental TEM 00 mode, suggesting that the Er:YSGG SCF can act as a promising candidate for mid-infrared laser seed source. • Er:YSGG single-crystal fiber(SCF) with a diameter of Φ 0.85 mm is prepared successfully. • Temperature distribution simulation shows the SCF possesses more efficient thermal dissipation. • 2794 nm CW laser power of 636 mW and beam quality factor M x 2 / M y 2 of 1.28/1.29 are achieved. • Er:YSGG SCF laser is a promising candidate for mid-infrared laser seed source. [ABSTRACT FROM AUTHOR]

• Laser performance of LD side-pumped YSGG/Er:YSGG with concave end-faces is studied. • The laser rods with negative curvature radii of 250, 500 and 1000 mm are employed. • Highest power of 20.92 W with slope efficiency of 26.18% at 150 Hz is achieved. • 15.59 W at 500 Hz is obtained in rod with negative curvature radius of 500 mm. • Thermal bonding and concave end-faces can effectively improve laser performance. We demonstrate the laser performance of 970 nm LD side-pumped YSGG/Er:YSGG/YSGG thermal bonding crystal rods with negative curvature radii of 250, 500, and 1000 mm, respectively. The maximum average output powers of 20.04, 20.92, 17.02 W are achieved, corresponding to the slope efficiencies of 26.28%, 26.18%, 21.28%, and optical–optical efficiencies of 18.56%, 19.37%, 15.76%, respectively. The results of the laser performance and thermal focal length indicate that the negative curvature of 500 mm has an optimal effect on thermal lensing compensation. At the high repetition rate of 500 Hz, the average output power of 15.59 W is obtained. The beam quality factors of M x 2/M y 2 are calculated to be 3.37/3.34. These results can provide valuable references for promoting the development of 2.7–3 μm lasers. [ABSTRACT FROM AUTHOR]

We report on the spectroscopic and laser performance of a novel 30 at.% Er:LuYSGG mixed crystal grown by Czochralski method. The XRC result shows the crystal has a high crystalline quality. A strong absorption peak is located at 966 nm with a FWMH of about 11 nm. The lifetimes of the upper 4I 11/2 and lower 4I 13/2 levels are 1.91 ms and 6.53 ms, respectively. A maximum output power of 909 mW with LD end-pumping is achieved, corresponding to optical-to-optical conversion efficiency of 18.1% and slope efficiency of 21.6%. The laser wavelength of 2794 nm and beam quality factors M x 2 /M y 2 of 1.78/1.83 are displayed. These results indicate that Er:LuYSGG mixed crystal is a promising gain medium for 2.8 μm laser. • The Er:LuYSGG mixed crystal with high optical quality was grown by the Cz method. • It has a longer upper laser level lifetime of 1.91 ms. • A maximum output power of 909 mW with LD end-pumping was obtained. • Results indicate the Er:LuYSGG is a promising gain medium for 2.8 μm laser. [ABSTRACT FROM AUTHOR]

Highlights • Four Cr,Er:YSGG crystal were processed with the size of Ø 3–6 mm × 105 mm. • A maximum pulse energy 1261 mJ operated at 5 Hz and 2.79 μm. • The formula of the thermal focal length is modified further. • Simulation results of the thermal focal lengths consist with the experiments well. Abstract We demonstrate the laser and thermal properties on the four Cr,Er:YSGG crystal rods with different diameters from 3 to 6 mm. A maximum pulse energy 1261 mJ operated at 5 Hz and 2.79 μm is obtained on the rod of 4 mm diameter, corresponding to electrical-to-optical efficiency of 1.53% and slope efficiency 1.82%, respectively. Combining with the electrical-to-optical efficiency and thermal distribution, the formula of the thermal focal length is modified further. The simulation results of the thermal focal length for four crystals with different diameters are in good consistence with the measurement values, suggesting the revised formula is accurate and effective to calculate the thermal focal length. [ABSTRACT FROM AUTHOR]

Er3+-doped YSGG crystals with nine different concentrations were grown successfully by Czochralski (Cz) method. The absorption, emission spectra, and the fluorescence decay curves are investigated comparably. Based on Judd–Ofelt (J–O) theory, the J–O intensity parameters Ω t (t = 2, 4, 6), the experimental and theoretical oscillator strengths are calculated with the absorption spectra. The results show that the 1 at. % lowly Er3+-doped YSGG crystal is more properly used in up-conversion laser applications and 5 at. % Er:YSGG crystal is a better candidate for 1.5 μm lasers within these nine crystals, while the heavily Er3+-doped YSGG crystal is beneficial for the 2.7 μm laser output. But if the doping concentration goes too high, the up-conversion rate of the 4I 11/2 level could be higher than that of the 4I 13/2 level, which would lead to increasing the up-conversion emission and quenching the mid-infrared emission. The 2.79 μm laser performance of LD end-pumped 40 at. % Er:YSGG crystal is also demonstrated. • Er:YSGG crystals with nine different concentrations were grown by Cz method. • The luminescence properties of Er3+ in YSGG crystals are fully researched. • 1 at. % Er:YSGG crystal is more suitable for up-conversion laser applications. • 5 at. % Er:YSGG crystal is a better candidate for 1.5 μm lasers. • A maximum power of 409 mW is obtained at LD end-pumped 40 at. % Er:YSGG. [ABSTRACT FROM AUTHOR]

• The 25 at. % Er:YSGG crystal with higher homogeneity was grown by Cz method. • A maximum power of 11.81 W with slope efficiency of 10.49% is realized at 500 Hz. • The laser center wavelength is located at 2794 nm and M2 x /M2 y are 7.01/7.10. • The Er:YSGG rod with concave end faces could be operated at high repetition rate. We demonstrate the laser performance of high repetition frequency on a 970 nm laser diode (LD) side-pumped Er:YSGG crystal rod with concave end faces. The laser performance under different repetition rates and pulse widths was studied with an optimal cavity length. The maximum average output power of 11.81 W operated at a repetition frequency of 500 Hz and 2.794 μm was achieved, corresponding to the slope efficiency of 10.49%. In addition, the beam quality factors M2 x /M2 y of 7.01/7.10 and far-field divergences Θ x /Θ y of 9.15/9.18 mrad were also obtained under the high repetition frequency of 500 Hz. These results show that the LD side-pumped Er:YSGG laser crystal rod with concave end faces has the potential of being operated under high repetition frequency. [ABSTRACT FROM AUTHOR]