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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]

We demonstrate the temperature distribution, optical and laser performances of a YAP/Tm:YAP/YAP composite crystal fabricated by thermal bonding technology. The thermal distribution simulations show that the bonded crystal possesses a higher thermal dissipation efficiency than that of the unbonded one. The wavefront distortion of the bonded YAP/Tm:YAP crystal is close to the unbonded Tm:YAP, indicating a high bonding quality. The optical transmission spectra and absorption loss suggest that the bonding region is a uniform transition and almost without scattering interface. Moreover, compared with the un-bonded Tm:YAP crystal, a maximum average output power of 41.2 W and slope efficiency of 49.5% are achieved on the bonded crystal, which are increased by 28.4% and 21.0%, respectively. Therefore, the 1.94 μm laser performance can be effectively improved by combining pure YAP crystals on the Tm:YAP crystal as end-caps. [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]

KTaO3 (KT) is an important material for optoelectronic and tunable microwave applications. However, growing large size and uniform crystals still remain a challenge. In this paper, a promising approach for growing relatively large size and high-quality KT single crystal was explored, and a transparent KT single crystal with dimension of Ф 30 × 80 mm, weighing as much as 406 g, was grown by Czochralski method successfully. The full width at half maximums (FWHMs) of X-ray rocking curves (XRCs) are 0.016°, 0.011°, and 0.016°, respectively, implying that the KT crystal possesses high crystalline quality. A comprehensive investigation of its mechanical, thermal, and optical properties was carried out. The Mohr's hardness is obtained to be 6.0, indicating that the KT is more conducive to being processed compared with diamond. The Sellmeier equation is fitted and the refractive index curve in the range of 400–3000 nm is displayed based on the measured refractive index. All results are of great significance for the further research and application of KT crystal. [ABSTRACT FROM AUTHOR]

Tm3+ doped YAlO3 (Tm:YAP) crystals with different concentrations were grown successfully by Czochralski method. The full width at half maximum of 0.007–0.008° shows high crystalline quality. The shape of dislocation etching pit is consistent with its crystal structure. The absorption spectra show an intensive peak located at 794 nm. The fluorescence lifetimes of 6.06, 4.68, 4.22, 4.01, and 1.93 ms decrease monotonically with the increase of Tm3+ concentration in the range of 2–7.5 at%. The fluorescence spectra exhibit two strong peaks appeared near 1775 and 1853 nm, respectively. Among them, the 4 at.% Tm:YAP crystal possesses the largest fluorescence intensity at 1853 nm, indicating that it is a promising gain material operated at ~ 1.9 μm for the development of diode-pumped solid-state lasers and the dopant concentration larger than 4 at.% may cause decline in laser performance owing to larger reabsorption loss and higher nonradiative decay rate. [ABSTRACT FROM AUTHOR]

We demonstrate the laser performance of a LD end-pumped Er:YSGG crystals with different doping concentrations comparatively. The experimental results show that 30 at. % Er:YSGG crystal with dimensions of 2 mm × 2 mm × 8 mm has the best laser output. In continuous-wave (CW) mode and pulse mode, the maximum output powers of 1.37 and 1.20 W are achieved, corresponding to slope efficiencies of 23.62% and 22.91%, respectively. To the best of our knowledge, compared with other Er3+-doped garnet laser crystals, we obtained a larger power and higher efficiency CW laser simultaneously for LD end-pumped Er:YSGG crystal. The beam quality factor M2 in x and y directions are determined to be 1.64/1.65, suggesting the Er:YSGG laser possesses a higher beam quality. All these results indicate that Er:YSGG is a promising mid-infrared gain medium for high efficiency and high power laser operation. [ABSTRACT FROM AUTHOR]

Highlights • High quality Cr,Er:YAG crystal was grown successfully by the Czochralski method. • Maximum single-pulse energies of 0.99 and 1.52 J are obtained on Er:YAG and Cr,Er:YAG. • Slope efficiencies are 1.31% and 1.80% for Er:YAG and Cr,Er:YAG, respectively. • Cr3+ can improve laser efficiency of Cr,Er:YAG without affecting beam quality. • Cr,Er:YAG may be a potentially mid-infrared radiation-resistant laser material. Abstract We demonstrated an improvement of laser performance by co-doping Cr3+ into Er:YAG crystal grown by the Czochralski method. The result of X-ray rocking curve suggested that the crystal had high crystalline quality. Two strong absorption bands centered at 450 and 596 nm indicated the Cr,Er:YAG crystal was more suitable for xenon lamp pumping. A maximum single pulse energy of 1.52 J was obtained on the Cr,Er:YAG crystal operated at 5 Hz and 2.94 μm, corresponding to the slope efficiency and electrical-to-optical efficiency of 1.80% and 1.28%, but those of the Er:YAG crystal were only 0.99 J, 1.31% and 0.83%, respectively. Therefore, the Cr,Er:YAG crystal may be a potentially mid-infrared radiation-resistant laser material with higher single pulse energy and efficiency. [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]

We demonstrate a high-peak-power and narrow pulse mid-infrared (MIR) laser with xenon-lamp pumping and La3Ga5SiO14 (LGS) Q-switching on the Cr,Er:YAP crystal grown by Czochralski method. X-ray powder diffraction and x-ray rocking curves suggest the crystal has high crystalline quality. Segregation coefficients of the Cr3 + and Er3 + in the as-grown Cr,Er:YAP crystal are 4.96 and 1.07, respectively. The absorption and fluorescence spectra indicate that the Cr,Er:YAP crystal is a promising material for MIR laser by xenon-lamp pumping. The fluorescence lifetimes of the upper (I11/24) and lower (I13/24) laser levels are 0.86 and 3.57 ms, respectively. A maximum energy of 632 mJ is acquired at 5 Hz by xenon lamp pumping. By the LGS electro-optic Q-switching technology, single pulse energy of 148.6 mJ is achieved at 5 Hz with a pulse width of 35.4 ns and peak power of 4.2 MW. The results show that the LGS Q-switched Cr,Er:YAP crystal pumped by xenon lamp possesses potential application as a short-pulse and high-energy laser device. [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]

• 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]

A series of Ho and Pr doped LuYSGG laser crystals were successfully grown by Czochralski method. X-ray rocking curves indicate their high crystalline quality. Crystal structure and basic parameters are provided by XRD and Rietveld refinement. Combining density functional theory, the bandgaps of YSGG and LuYSGG are calculated to be 3.497 and 3.483 eV, respectively. Particularly, the J-O parameters and emission spectra suggest the LuYSGG is more suitable as host for Ho3+ ions and could achieve better 2.9 μm emission than the YSGG. Meanwhile, the luminescent decay curves show the deactivated Pr3+ ion can greatly narrow the lifetime gap between the 5I 6 and 5I 7 energy levels, which can eventually attenuate effect of self-termination phenomenon on the 2.9 μm emission. • A series of Ho and Pr doped LuYSGG mixed laser crystals are prepared. • Microscopic and bandgap structure of LuYSGG are investigated in detail. • LuYSGG is more suitable for achieving Ho:2.9 μm emission than YSGG. • Pr can effectively attenuate the 2.9 μm self-termination phenomenon. [ABSTRACT FROM AUTHOR]

Er3+-doped YAP crystals with concentrations of 5 at%, 10 at%, 15 at% and 20 at% were grown successfully by Czochralski method. X-ray rocking curves suggest high crystalline quality. Lifetime ratio of 4I 13/2 and 4I 11/2 levels decreases obviously with the increase of Er3+ concentrations, which is beneficial to realize population inversion and decrease the laser threshold. Spectroscopy and laser show the 15 at% Er:YAP crystal has strongest mid-infrared fluorescence intensity and best laser performance by 968-nm LD side-pumping. Maximum average powers of 23.52 and 11.08 W are achieved at 250 and 1000 Hz, corresponding to the slope efficiency of 12.0% and 6.2%, respectively. Therefore, the 15 at% Er:YAP crystal is a promising candidate for the high-power and high-frequency mid-infrared laser. • High-quality Er:YAP crystals with four concentrations were grown by the Cz method. • Influences of Er3+ concentrations on the performance of Er:YAP crystals were studied. • Energy transfer and luminescence mechanism in the Er:YAP crystals were analyzed. • LD side-pumped high-power and high-frequency Er:YAP laser is demonstrated. • Maximum average power of 23.52 W was obtained on the 15 at% Er:YAP crystal. [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]

Abstract Er3+ and Pr3+ co-doped YAP laser crystal with high optical quality was grown successfully by the Czochralski method for the first time. By contrast, an Er3+ single doped YAP laser crystal was also grown. The cell parameters of the two crystals were obtained by the X-ray Rietveld refinement method. The X-ray rocking curves indicate that the as-grown crystals possess excellent crystalline quality. The absorption spectra show that the crystals are suitable to be pumped by 972 nm LD. The NIR and MIR emission spectra, the up–conversion spectra and the fluorescence decay curves were also measured to investigate the influence of Pr3+ ions on the spectroscopic properties. The results indicate the Pr3+ ions acting as the deactivator can decrease efficiently the lifetime of the lower laser level 4I 13/2 of the Er3+ ions from 10.72 to 0.489 ms, which would be beneficial to decrease the laser threshold and increase the laser conversion efficiency. Highlights • XRCs show Er:YAP and Er,Pr:YAP crystals possess high crystalline quality. • Pr3+ deactivator reduces 4I 13/2 lifetime from 10.72 to 0.489 ms, benefiting to decrease threshold and improve efficiency. • NIR and UC fluorescence provide further evidence that Pr3+ ions can efficiently depopulate Er3+ ions at 4I 13/2 level. • All results indicate the Er,Pr:YAP crystal is a promising laser medium for realizing a 2.7 μm laser pumped by 970 nm LD. [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]