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We report on a 928 nm laser based on quasi-three-level transition of 4F3/2 → 4I9/2 in a Nd:Gd0.69Y0.3TaO4 mixed single crystal. With LD pumping at 808 nm, an output energy of 29.8 mJ at 928 nm is achieved with an optical-to-optical efficiency of 16.5% and a slope efficiency of 21.2%. In comparison, using 879 nm LD pumping, the maximum output energy at 928 nm reaches 48.5 mJ with an optical-to-optical efficiency of 33.4% and a slope efficiency of 38.0%.

A promising 2.9 µm Ho:GdYTaO4 laser crystal was grown successfully by the Czochralski method for the first time. The crystal belongs to the monoclinic space group of I2/a (No. 15) and high crystalline quality is demonstrated by X-ray rocking curves. The spectral properties of Ho:GdYTaO4 crystal at room temperature are investigated. Based on the Judd–Ofelt theory, the intensity parameters, spontaneous transition probabilities, fluorescence branching ratios, and radiative lifetimes are obtained in detail. The strongest emission peak is located at 2848 nm, and the full width at half maximum is about 15 nm. The experimental lifetimes of 5I6 and 5I7 levels are 0.31 and 8.08 ms, respectively. Moreover, the Stark levels of 5I6, 5I7, and 5I8 are identified and the splitting values are calculated to be 254.1, 226.7, and 370. 4 cm−1, respectively.

A diode-pumped acousto-optically (AO) Q-switched 1066 laser with a novel Nd:Gd0.69Y0.3NbO4 crystal under 879 nm pumping was demonstrated for the first time. In CW operation, the maximum output power of 7.5 W was obtained with a slope efficiency of 37.6%. The different modulation repetition rates from 5 kHz to 30 kHz in the pulsed Nd:GdYNbO4 laser were investigated. At an absorbed pump power of 7.44 W and a repetition rate of 10 kHz, the pulse width and peak power were 17.8 ns and 6.75 kW, respectively. We also got the highest repetition rate 61.214 kHz of this new mixed crystal.

In this paper, we present the acousto-optical (AO) Q-switched performance of a holmium (Ho):gadolinium tantalate (GdTaO4) (Ho:GTO) laser pumped by a thulium (Tm)-fiber laser emitting at 1.94 µm. In the efficient continuous wave (CW) regime, a maximum output power of 30.5 W at 2068.8 nm was achieved, corresponding to a slope efficiency of 74.9% with respect to the absorbed pump power. In the Q-switching regime, pulse energies of 2.4 mJ, 1.2 mJ, and 0.9 mJ were obtained with pulse repetition frequencies of 10 kHz, 20 kHz, and 30 kHz, respectively. The minimum pulse widths were 18 ns, 23 ns, and 26 ns, corresponding to peak powers of approximately 133.3 kW, 52.2 kW, and 34.6 kW, respectively.

30 at% Er3+:GSAG single crystal was successfully grown by the Czochralski method. The dislocation of (111) face is studied using the chemical etching with the phosphoric acid etchant. The luminescence properties at 2.6–3.0 µm are systematically studied by measuring the fluorescence spectra and lifetimes to the transition of 4I11/2 → 4I13/2. The long fluorescence lifetime, high fluorescence intensity, and large gain σem spectra indicate that the 30 at% Er:GSAG crystal has the great potential for the multi-wavelength laser output at 2.6–3.0 µm. Meanwhile, the absorption and fluorescence properties of 30 at% Er:GSAG crystal under the gamma-ray radiation with three different intensities (35, 70, and 105 Mrad) have been investigated, indicate that this crystal can be considered as a promising MIR laser gain medium for being used under radiant environment. In addition, the luminescence property of 30 at% Er:GSAG crystal in visible and 1.5–1.7 µm was also studied, which shows the possibility to generate the laser around 1.6 µm.

We demonstrate for the first time a Cr4+:YAG passively Q-switched 1066 nm pulse-burst laser under 879 nm direct pump with a novel Nd:Gd0.69Y0.3NbO4 crystal. The output laser characteristics with different pump repetition rates and different Cr4+:YAG initial transmission are studied. Without the Cr4+:YAG, we obtain a maximum output energy of 2.55 mJ at an absorbed pump energy of 5.79 mJ with the highest 48% slope efficiency. The pulse-burst laser contains a maximum of 7 pulses for a Cr4+:YAG initial transmission of 55% and a pump repetition rate of 1 kHz. The single-pulse energy and narrowest pulse width reach 160 μJ and 5.5 ns at 38.2 kHz, with a peak power of 32 kW.

A diode-pumped 1347 nm laser with a novel Nd:GdNbO4 crystal is demonstrated for the first time to our best knowledge. Laser performance around 1.3 μm under 879 nm laser diode pumping is investigated with different output mirrors, pump radii and repetition rates. A maximum average power of ∼ 373 mW at 1347 nm is achieved at 50 Hz, corresponding to an optical-to-optical efficiency of 5.5% and a slope efficiency of 6.8%.

Saturable absorber (SA) based on antimony telluride (Sb2Te3)-graphene oxide (GO) had been fabricated. We demonstrated a compact passively Q-switched Nd:GGG laser with the mixed Sb2Te3-GO SA. Stable Q-switching operation at a central wavelength of 1066 nm was performed. The shortest single pulse width of 237 ns with repetition rate of 72 kHz and the maximum output power for Q-switched operation of 408 mW was achieved under the pump power of 4.5 W, corresponding to the optical-to-optical conversion of 9.1%.

Er3+ doped GSAG laser crystal with high optical quality was grown successfully by the Czochralski method for the first time. The structural parameters and the high crystalline quality of this crystal were determined. Judd-ofelt (J-O) parameterization scheme was applied to analyze the absorption spectra at room temperature. Accordingly, the lines strengths, oscillator strengths, transition probabilities, fluorescence branching ratios, and radiative lifetimes were calculated to characterize the laser properties of Er:GSAG crystal. Additionally, the fluorescence spectra and lifetimes of Er:GSAG crystal were measured and studied. The stimulated emission cross-section spectra and gain cross-section spectra were evaluated for 4I13/2 →4I15/2 (1.5–1.6 µm) transitions which indicate high potential of 1 at% Er:GSAG for laser emissions at 1567 and 1605 nm. Furthermore, the possibility of Er:GSAG crystal to realize the visible laser output pumped by the GaN LDs were initially studied and analyzed.

1 at% Er 3+ doped Er: GdTaO 4 laser crystal with high optical quality was successfully grown by the Czochralski method. The structural parameters were obtained by the X-ray Rietveld refinement. A high crystalline quality of Er: GdTaO 4 was determined by the X-ray rocking curve. The transition intensity parameters of Er 3+ ions were fitted according to the absorption spectra along three principal polarization directions. The relatively larger emission cross section (1.022×10 −20 cm 2 ), long fluorescence lifetime ( 5.66 ms) and relatively weaker reabsorption phenomenon around 1.6 µm indicate that 1 at% Er: GdTaO 4 crystal can be used as a promising NIR laser material. Meanwhile, the stimulated emission cross-section spectra along three principal polarization directions were investigated for 4 I 13/2 → 4 I 15/2 transitions at 1.5–1.6 µm which indicates a great potential of Er: GdTaO 4 for multi-wavelength emission at 1.5–1.6 µm. In addition, the possibility of generating green and red lasers in Er: GdTaO 4 was also analyzed and evaluated.

In this work, harmonic mode locking in a laser diode pumped passively Q-switched mode-locked Nd:GdTaO4 1066 nm laser is presented by using Cr4+:YAG as saturable absorber. The average output power of the passively Q-switched mode-locked 1066 nm laser reaches 4.7 W with a repetition rate of 200.0 MHz and a pulse width of ~1.3 ns within a Q-switched envelope of 150.0 ns. By changing the Z-type cavity length, high-order harmonic mode locking operation of the passively Q-switched 1066 nm laser is conducted. The 3rd-order harmonically mode-locked 1066 nm laser yields a maximum average output power of 3.2 W and a pulse width of ~570 ps at 164.5 MHz repetition rate inside a Q-switched envelope of 419.7 ns long. The pulse repetition rate reaches 655.3 MHz in the 9th-order harmonically mode-locked 1066 nm laser.

This study investigated the laser performance of a Nd:GdYTaO4 crystal in continuous-wave and acousto-optically Q-switched operation. Laser performance comparison was conducted under 808 nm and 879 nm laser diode (LD) pumping. In continuous-wave operation, the maximum power at 1066 nm reached 4.4 W with an optical-to-optical efficiency of ~33.6% and the slope efficiency was ~35.9% under 808 nm laser diode pumping. In comparison, an output power of 7.7 W with an optical-to-optical efficiency of ~47.8% and a slope efficiency of ~48.3% were achieved in 879 nm LD pumped 1066 nm laser. Under 808 nm LD pumping, the Nd:GdYTaO4 crystal yielded an average output power of 1.1 W and a pulse width of 59.5 ns at the repetition rate of 30 kHz. By using direct pumping directly into the 4F3/2 emitting level, the average power was increased to 1.9 W and the pulse width was shortened to 33.0 ns at the repetition rate of 30 kHz.

This study investigated the laser performance of a Nd:GdTaO4 crystal for the 4F3/2→4I9/2 and 4F3/2→4I13/2 transitions at 928 nm and 1328 nm, respectively. A 5-mm-thick, 1.4 at.% Nd:GdTaO4 crystal was used in the experiments, under a pump at 879 nm, directly into the 4F3/2 emitting level. At a 10 Hz pump repetition rate, the maximum pulse energy at 928 nm reached 35.7 mJ, with an optical-to-optical efficiency of ~19.3%. When the pump repetition rate increased to 100 Hz, the laser pulse energy decreased to 13.5 mJ; the laser beam was characterised by M2 factors of Mx2 = 1.4 and My2 = 1.8 for the Ox and Oy axis, respectively. The Nd:GdTaO4 crystal yielded laser pulses at 1328 nm with a maximum energy of 9.7 mJ for operation at 10 Hz repetition rate; the overall optical-to-optical efficiency amounted to ~5.2%. Increasing the pump repetition rate to 100 Hz reduced the laser pulse energy to 5.8 mJ; the laser beam M2 factors were Mx2 = 1.2 and My2 = 1.4.

In this paper, self-Q-switched (SQS) and passively Q-switched mode-locked (QML) dual-wavelength Nd:YSAG lasers are reported, that works at 1058.97 and 1061.49 nm, simultaneously. Till now, the performance on SQS, and passively QML operation by using black phosphorus (BP) in Nd:YSAG crystal lasers have not been reported as per the author’s knowledge. The Nd:YSAG laser SQS operation was realized by designing a simple plano-plano resonator cavity. The maximum output power of 0.471 W at absorbed pump power 2.64 W and the pulse duration was 885 ns. The Nd:YSAG laser QML operation was realized by designing a Z-type resonator cavity. The duration of mode-locked pulse inside the Q-switched envelop was estimated to be 235 ps with 96.5 MHz repetition rate at the absorbed pump power of 4.08 W in QML with black phosphorus saturable absorber (BP-SA).

A new promising 2.9 μm Tm,Ho:GdYTaO4 (Tm,Ho:GYTO) laser crystal was grown by the Czochralski method. The full width at half maximum (FWHM) of X-ray rocking curve on the (0 1 0) face is only 0.05°, which indicates that the crystal has high crystalline quality. The structure parameters of Tm,Ho:GYTO crystal were determined by Rietveld refinement method. Chemical etching is employed to investigate the defect structure of Tm,Ho:GYTO crystal with KOH etchant. The absorption, emission spectra, and level lifetimes were measured, and the corresponding absorption transitions were assigned. The absorption cross-section at 790 nm was calculated to be 2.04 × 10−20 cm2 and maximum emission-cross section at 2932 nm was 2.05 × 10−20 cm2. The level lifetimes of 5I6 and 5I7 are 131 μs and 4.09 ms, respectively. Compared with other hosts, such as Ho:YAG, the shorter lifetime of 5I7 and long lifetime of 5I6 in the Tm,Ho:GYTO crystal are easier to realize population inversion. The Tm–Ho energy transfer mechanism in GYTO is also demonstrated.

A new crystal of Yb-doped gadolinium niobate, 5 at.% Yb:GdNbO 4 , is grown by Czochralski method for the first time. The structure of Yb:GdNbO 4 is determined by Rietveld refinement to the X-ray powder diffraction data and it belongs to the monoclinic space group of I 2/a . With the center of 955 nm, the FWHM of absorption spectra is 57 nm and the absorption cross section is calculated to be 0.97 × 10 −20 cm 2 . Spectral parameters are calculated with absorption spectrum. In emission spectra, the strongest peak is at 1001 nm and the FWHM is 49 nm. In comparison with corresponding emission cross section of Yb:YSO and Yb:GSO, Yb:GdNbO 4 exhibits a relatively larger emission cross section. In addition, a maximal output power of 270 mW is obtained and the slope efficiency is 7.5%.

Recently, we proposed GdTaO4 as a promising high-density scintillator but the scintillation mechanism was still unknown. In this paper, we investigated the temperature-dependent luminescent properties of GdTaO4 crystal. The emission spectra are characterized by a broad band composed of two Gaussian components located at ~2.2 eV and ~2.7 eV of 8–300 K, which are both thermally quenched with the activation energy of 156 meV and 175 meV, respectively. These two bands are believed to be from different luminescent centers, judging from the excitation spectra, thermal activation energy and decay curves. Additionally, it was also found that the annealing atmosphere exerts little influence on the luminescence intensity. Based on the results, we tentatively assigned the high-energy band to self-trapped excitons (STE) localized in TaO 4 3 − groups and the low-energy band to relaxed excitons related to lattice imperfections.

Based on Faraday effect we demonstrate a thulium fiber pumped continuous-wave single-longitudinal-mode laser with a new Ho:GdTaO4 crystal. By inserting a faraday rotator and a half-wave plate into the laser cavity, the single-longitudinal-mode output power of 392 mW at wavelength of 2068.33 nm was obtained in unidirectional Ho:GdTaO4 ring laser, corresponding to a slope efficiency of 60.2% respect to the absorbed pump power. Furthermore, utilizing the Ho:GdTaO4 power amplifier, the maximum single-longitudinal- mode output power of 1.02 W was achieved.

We report an 879 nm laser diode directly pumped passively Q-switched Nd:GdTaO4 laser at 1066 nm. The continuous-wave output power at 1066 nm reaches 5.6 W under an incident pump power of 12.8 W, corresponding to an optical-to-optical efficiency of 43.8% and a slope efficiency of 48.0%. By using Cr4+:YAG as the saturable absorber, passively Q-switched laser operation is conducted, yielding a highest pulse repetition frequency of 185 kHz and a maximum average power of 3.6 W. The shortest pulse width of 15.2 ns is achieved with a peak power of 2.34 kW at 33.7 kHz. The beam quality factors at the maximum average output power is measured to be Mx2 = 2.2, My2 = 1.5 by using knife-edge method. The thermal focal length and internal loss for Nd:GdTaO4 crystal is also investigated.

Large size high transparent TSAG and TSLAG single crystals of O 65 mm × 70 mm have been grown successfully by the Cz method. The refractive indices at 473, 532, 632.8 and 1064 nm are 1.9214 - 1.8817 for TSAG and 1.9242 - 1.8841 for TSLAG. Their Sellmeier equations are fitted. The average thermal expansion coefficients of TSAG and TSLAG at 300 – 373 K, 300 – 473 K, 300 – 573 K, 300 – 673 K, and 300 – 773 K are measured. The values of thermal expansion coefficients of TSAG and TLSAG crystals coincide within the measurement error (differ by 0.3–0.4%). The thermal diffusivity values of TSAG and TSLAG are 1.454 and 1.418 mm2 s−1 at 300 K, respectively. Calculated with the specific heat results, the values of thermal conductivity of TSAG and TSLAG are 4.45 and 4.20 W (m K)−1 at 300 K. Moreover, the Verdet constants of TSAG are 218, 152, and 65 rad/m/T at 532, 633, and 1064 nm, while those of TSLAG are 246, 146, and 56 rad/m/T, respectively. In further, the relationships between Verdet constant and wavelength of TSAG and TSLAG are obtained.

We demonstrate a continuous-wave 2.1-µm laser with a new Ho:GdTaO4 crystal pumped by a 1940.3-nm Tm fiber laser at room temperature. The maximum output power of 11.2 W at 2068.39 nm was achieved, corresponding to a slope efficiency of 72.9%. Moreover, the beam quality factor was measured to be about 1.4 at the maximum output level.

We demonstrate a 968 nm diode end-pumped Er:GYSGG (Gd1.17Y1.83Sc2Ga3O12) laser at 2.796 μm operated in the pulse and continuous-wave (CW) modes. A maximum laser energy of 2.43 mJ is obtained at a pulse width of 2 ms, corresponding to a peak power of 1.25 W and a slope efficiency of 7.2%. In the CW mode, the maximum output power is 348 mW, corresponding to an optical–optical conversion efficiency of 9.2% and a slope efficiency of 10.1%. The M2 factor is 1.94, and the beam divergence is 6.4 mrad. Gamma irradiation at 100 Mrad only slightly affects laser output performance. This result suggests that Er:GYSGG crystal is a potentially new mid-infrared radiation-resistant laser material that can be applied in space and ionizing radiation environment.

We report an 879 nm laser diode (LD) end-pumped quasi-three-level 927 nm laser with a Nd:GdYNbO4 mixed crystal for the first time to the best of our knowledge. Comparing the 927 nm laser's performance under 808 nm and 879 nm LD pumping, we find performance enhancement is achieved by using direct 879 nm LD pumping. A maximum output energy of 42 mJ at 10 Hz is obtained in the 879 nm LD pumped 927 nm laser with an optical-to-optical efficiency of 24% and a beam quality factor of M 2 = 1.7. The dependence of output characteristics on the pumping repetition rate is discussed. The average output power at 927 nm reaches 1.13 W at 100 Hz with an optical-to-optical efficiency of 6.5%.

We demonstrated an 879-nm-diode-pumped Nd:Gd0.69Y0.3TaO4 laser in continuous-wave-(CW), pulse-pumped, pulse-reflection-mode Q-switched, and cavity-dumped burst-mode Q-switched operations for the first time. A maximum output power of 9.3 W at 1,066 nm was obtained in the CW operation with a slope efficiency of ~48%. The slope efficiency reached the value of ~68% in the pulse-pumped operation. A peak power of 150 kW and pulse width of 3.4 ns were obtained in the cavity-dumped burst-mode Q-switched operation at a Q-switching repetition rate of 20 kHz.

Laser performances around 1.3 μm are investigated in 879 nm laser diode (LD) end pumped Nd3+ doped mixed crystals with Nd:Gd0.69Y0.3TaO4 and Nd:Gd0.68Y0.3NbO4 crystals for the first time to our best knowledge. The maximum average power in LD end pumped Nd:Gd0.69Y0.3TaO4 1328 nm laser reaches 435 mW at 50 Hz with an optical-to-optical efficiency of 5.0% and a slope efficiency of 6.9%. In comparison, the highest average power of LD end pumped Nd:Gd0.68Y0.3NbO4 laser at 1337 nm is 190 mW at 50 Hz, corresponding to an optical-to-optical efficiency of 3.5% and a slope efficiency of 4.2%.

We demonstrate a 968 nm diode end-pumped Er,Pr:GYSGG (Gd₁.₁₇Y₁.₈₃Sc₂Ga₃O₁₂) laser at 2.79 μm operated in the pulse and continuous-wave (CW) modes. The lifetimes for the upper laser level ⁴I₁₁/ ₂ and lower level ⁴I₁₃/₂ are 0.52 and 0.60 ms, respectively. The laser produces 284 mW of power in the CW mode, corresponding to the optical-to-optical efficiency of 14.8% and slope efficiency of 17.4%. The maximum laser energy achieved is 2.4 mJ at a repetition rate of 50 Hz and pulse duration of 0.5 ms, corresponding to a peak power of 4.8 W and slope efficiency of 18.3%. These results suggest that doping deactivator Pr3+ ions can effectively decrease the lower-level lifetime and improve the laser efficiency.