Guihua Sun

A promising high-density scintillator of GdTaO4 single crystal

A crack-free GdTaO4 single crystal as a promising high-density scintillator is grown successfully by the Czochralski method. High crystalline quality of the as-grown crystal has been demonstrated by its X-ray rocking curve. Its density is 8.94 g cm−3, which is the highest among current inorganic single-crystal scintillators. The absolute light yield of GTO is about three times as that of PbWO4 and the scintillation decay consists of a fast component of 72.6 ns and a slow component of 1236.2 ns. Additionally, the photoluminescence measurements of GTO indicate a complicated mechanism. Its fundamental physical properties including hardness, density, and thermal properties are determined for the first time, which are very important for crystal growth and its applications.

Diode-pumped passively dual-wavelength Q-switched Nd:GYSGG laser using graphene oxide as the saturable absorber.

The performance of a diode end-pumped passively Q-switched dual-wavelength Nd:GYSGG laser operating at 1057.28 and 1060.65 nm with graphene oxide as the saturable absorber was demonstrated. The maximum dual-wavelength average output power of 521 mW was achieved under the absorbed pump power of 5.4 W, corresponding to the optical-to-optical conversion and slope efficiency of 9.8% and 21%, respectively. The minimum pulse width was 115 ns with a pulse repetition rate of 338 kHz.

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, 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.

Diode-pumped passively Q-switched Nd : GdNbO4 laser with Cr4+ : YAG saturable absorber

Diode-pumped passively Q-switched laser operation of a Nd:GdNbO4 crystal at 1066 nm using Cr4+:YAG as a saturable absorber was demonstrated for the first time. Using two different Cr4+:YAG crystals with initial transmission of 95% and 90% as the saturable absorber for Q-switching, a maximum average output power of 0.50 and 0.41 W was obtained at a pulse repetition frequency of 28.7 and 17.8 KHz, respectively. The shortest pulse width of 23 ns, the largest pulse energy of 22.7   μ J, and the highest peak power of 974.1 W were obtained when the Cr4+:YAG crystal was used with an initial transmission of 90%. The shortest pulse width of 33.3 ns, the largest pulse energy of 17.3   μ J, and the highest peak power of 519 W were obtained when the Cr4+:YAG crystal was used with an initial transmission of 95%. All the results indicate that the Nd:GdNbO4 crystal is a material suitable for diode-pumped passively Q-switched lasers.

Crystal growth and characterization of a mixed laser crystal: Nd-doped Gd0.89La0.1NbO4

Herein, a Nd-doped GdLaNbO4 (Nd:GLNO) single crystal has been grown successfully using the Czochralski method. The segregation coefficient of Nd3+ ions in the Nd:GLNO crystal is measured to be 0.71. The X-ray power diffraction patterns of the Nd:GLNO crystal confirm that the as-grown crystal has the same crystal structure as pure GdNbO4. The structural parameters of the as-grown crystal are obtained via an X-ray Rietveld refinement method. The absorption spectrum, fluorescence spectrum, and fluorescence decay curve of Nd:GLNO were obtained at room temperature. The small emission cross-section at 1065 nm and long fluorescence lifetime of Nd3+ ions (176.4 μs) indicate that the Nd:GLNO crystal is suitable for generating an ultrashort pulse laser. A maximum continuous wave (CW) laser output power of 957 mW is achieved at 1.06 μm, corresponding to an optical-to-optical conversion efficiency of 30.3% and slope efficiency of 34.2%. All the obtained results imply that this crystal is a novel mixed niobate-based laser host suitable for laser diode pumps.

Dual-wavelength self-Q-switched Nd:GYSGG laser

A dual-wavelength self-Q-switched operation of Nd:GYSGG laser with different output couplers is proposed and demonstrated. In self-Q-switched operation, two laser lines between 1056.86 nm and 1060.23 nm were found. Under the pump power of 4 W, the shortest pulse width of 2.02 μs was obtained with a maximum average output power of 565 mW and the optical conversion efficiency of 14.13%. The pulse repetition rate and single pulse energy were 50.2 kHz and 11.25 μJ, respectively. The system is very stable and suitable for generation of multi-wavelength pulses.