Jianqiao Luo

Spectroscopic properties and diode end-pumped 2.79 μm laser performance of Er,Pr:GYSGG crystal

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.

Spectroscopic, diode-pumped laser properties and gamma irradiation effect on Yb, Er, Ho:GYSGG crystals

We demonstrate a diode end-pumped Yb, Er, Ho:Gd(1.17)Y(1.83)Sc(2)Ga(3)O(12) (GYSGG) laser operated at 2.79 μm in continuous-wave mode. Spectral analysis shows that Yb(3+) and Ho(3+) act as sensitizer and deactivator ions, respectively. Pumping with a 967 nm laser diode produces the maximum output power of 411 mW, corresponding to optical-optical conversion and slope efficiencies of 11.6% and 13.1%, respectively. The minimum laser threshold is only 81 mW because of Ho(3+) doping. The laser properties are only slightly influenced by 100 mrad gamma irradiation. The Yb, Er, Ho:GYSGG crystal possesses excellent radiation resistance and is a potential laser gain medium in radiant environments.

Thermal and Nonlinear Optical Properties of Ca4YO(BO3)3

Ca 4 YO(BO 3 ) 3 (YCOB) crystals have been grown using the vertical Bridgman method. The thermal properties of YCOB were measured for the first time to our knowledge. The specific heat is 729.7 J/kg K at 373K. The average thermal expansion coefficients along the a, b and c axes are 9.9×10 -6 /K, 8.2×10 -6 /K and 12.8×10 -6 /K. respectively, in the temperature range of 293-1173K. The thermal conductivities along the a, b and c axes are 1.83W/mK, 1.72W/mK and 2.17W/mK at 373K. The anisotropy in the measured thermal conductivities of YCOB is consistent with the experimental results of the thermal expansion. The SHG of a Nd: YAG laser was compared with that of a KDP crystal. The effective nonlinear coefficients (d eff ) of YCOB in type I phase matching directions of (θ, Φ)=(66.3°, 143.5°) and (65.9°, 36.5°) were estimated to be 1.45pm/V and 0.91pm/V, respectively. The bulk damage threshold was observed as 85GW/cm 2 for single pulse of a Nd:YAG laser with 10ns pulse duration.

Efficient Continuous-Wave 1053-nm Nd:GYSGG Laser With Passively Q-Switched Dual-Wavelength Operation for Terahertz Generation

Research on an efficient continuous-wave Nd:GYSGG laser at 1053 nm with excellent stability is demonstrated. The maximum output power is 4.17 W, corresponding to the conversion efficiency of 33.9% and the slope efficiency of 42.92%. Using a Cr:YAG absorber, pulsed dual-wavelength operation at 1053 and 1058.4 nm is obtained, of which the maximum single pulse energy and peak power are 172.1 μJ and 26.1 kW, respectively, when the pulse width is 6.6 ns and the repetition rate is 4.3 kHz. A polarization property is observed, owing to the anisotropy of Cr:YAG. This stably Q-switched dual-wavelength laser is a good pump source for the generation of a terahertz wave at 1.53 THz.

Growth, thermal properties, and LD-pumped 1066 nm laser performance of Nd^3+ doped Gd/YTaO_4 mixed single crystal

A new laser crystal Nd:Gd0.69Y0.3TaO4 (Nd:GYTO) with high quality was grown by Czochralski method. The physical properties, including temperature dependent density, specific heat, thermal expansion coefficient, and thermal conductivity, were systematically characterized. The maximum absorption cross section at 809 nm and the stimulated emission cross section at 1066.6 nm are 6.886 × 10−20 cm2 and 22 × 10−20 cm2, respectively. The fluorescence lifetime is measured to be 182.4 μs. Up to 2.37 W of continuous wave (CW) laser operating at 1066.5 nm has been successfully realized, corresponding to an optical conversion efficiency of 36.5% and a slope efficiency of 38%. Compared with Nd:GdTaO4, Nd:GYTO shows an enhancement of the laser performance. These results demonstrate that Nd:Gd0.69Y0.3TaO4 is a novel laser crystal with low symmetry and has great potential as low to moderate power lasers.

Growth, spectroscopy, and laser performance of a 2.79 μm Cr,Er,Pr:GYSGG radiation-resistant crystal.

We demonstrate the growth, spectroscopy, and laser performance of a 2.79 μm Cr,Er,Pr:GYSGG radiation-resistant crystal. The lifetimes for the upper laser level (4)I(11/2) and lower laser level (4)I(13/2) are 0.59 and 0.84 ms, respectively, which are due to the doping of the Pr(3+) ions. A maximum pulse energy of 278 mJ operated at 10 Hz and 2.79 μm is obtained when pumped with a flash lamp, which corresponds to the electrical-to-optical efficiency of 0.6% and a slope efficiency of 0.7%. A maximum average power of 2.9 W at 60 Hz is achieved, which corresponds to the electrical-to-optical efficiency of 0.4% and slope efficiency of 0.8%. Compared with a Cr,Er:YSGG crystal, the Cr,Er,Pr:GYSGG crystal can be operated at a higher pulse repetition rate. These results suggest that doping deactivator Pr(3+) ions can effectively decrease the lower laser level lifetime and improve the laser repetition rate. Therefore, the application fields and range of the Cr,Er,Pr:GYSGG laser can be extended greatly due to its properties of radiation resistance and high repetition frequency.

Performances of a diode end-pumped GYSGG/Er,Pr:GYSGG composite laser crystal operated at 2.79 μm.

We demonstrate a comparative investigation on Er,Pr:GYSGG and GYSGG/Er,Pr:GYSGG composite crystals at 2.79 μm. Simulating results show the highest temperatures are 369 K and 318 K, respectively. A maximum output power of 825 mW with slope efficiency of 19.2% and maximum laser energy of 3.65 mJ with slope efficiency of 22.7% are obtained in the GYSGG/Er,Pr:GYSGG composite crystal, which have an obvious improvement than those of Er,Pr:GYSGG crystal. The thermal focal lengths are respectively 41 and 62 mm when the pump power is 2.5 W. All these results indicate that the GYSGG/Er,Pr:GYSGG composite crystal has great advantages in reducing the influence of thermal effects and improving laser performances.

Growth, thermal, and spectroscopic properties of a 2.911 μm Yb,Ho:GdYTaO4 laser crystal

A promising 2.911 μm Yb,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 effective segregation coefficient keff of Yb, Ho, and Y are 1.08, 0.96, and 0.9, respectively, all close to 1. Crystal density is measured to be 8.59 g cm−3 by the buoyancy method. Thermal property indicates that the Yb,Ho,Y:GdTaO4 crystal should be pumped along the c-axis in order to reduce the thermal lensing effect. Strong absorption in the range of 900–1000 nm and emission at 2911 nm are obtained in the as-grown crystal. In comparison with corresponding level lifetimes of Yb,Ho:YSGG, Tm,Ho:LuAG, Tm,Ho:YAG, and Ho:YAG, the Yb,Ho,Y:GdTaO4 crystal exhibits a relatively shorter lifetime of 7.298 ms for lower laser level 5I7 and longer lifetime of 419 μs for upper laser level 5I6, which are beneficial to realize population inversion and laser output.

Growth, structure, and spectroscopic properties of a Cr3+, Tm3+, Ho3+, and Pr3+ co-doped LuYAG single crystal for 2.9 μm laser

A new laser crystal from Lu2.4Y0.6Al5O12 (LuYAG) co-doped with Cr3+, Tm3+, Ho3+, and Pr3+ ions was grown successfully by the Czochralski method for the first time. The structure parameters of the Cr,Tm,Ho,Pr:LuYAG crystal are determined by the X-ray Rietveld refinement method. The main absorption bands are observed near 426 and 782 nm, and the fluorescence spectrum excited by a 450 nm or 783 nm LD presents an emission band near 2.911 μm, indicating that the co-doped Cr3+ and Tm3+ ions can be utilized as sensitizers for the Ho3+ ions. The lifetimes of the 5I6 and 5I7 levels of the Ho3+ ions were measured and fitted to be 0.070 ms and 1.852 ms, respectively. The energy transfer efficiencies of the processes 5I6 (Ho3+) → 3F3,4 (Pr3+) and 5I7 (Ho3+) → 3F2 (Pr3+) + 3H6 (Pr3+) were calculated, showing that the Pr3+ ions can play the role of a deactivator for the Ho3+ ions. Furthermore, the energy transfer mechanisms among the Cr3+, Tm3+, Ho3+, and Pr3+ ions were studied. The results suggest that the Cr,Tm,Ho,Pr:LuYAG crystal is a new promising laser medium operating at around 2.9 μm under flash lamp or 783 nm LD pumping.

Continuous-wave Nd : GYSGG laser properties in 1.3 and 1.4 µm regions based on 4F3/2 to 4I13/2 transition

Continuous-wave laser properties of Nd : GYSGG crystal based on the transition from 4F3/2 to 4I13/2 are investigated. With different output couplers, single or multiple wavelength lasers operating at 1321, 1336, 1404 and 1424 nm are obtained, which provide new options in these wavelength bands. In the 1.3 µm region, the maximum output power is 2.5 W, corresponding to the conversion efficiency of 18.5%. In the 1.4 µm region, the maximum output power at 1424 nm is 707 mW, corresponding to the conversion efficiency of 6.8%. The output power and conversion efficiency can be improved with better anti-reflection coatings for the laser crystal.