Qingli Zhang

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.

Efficient diode-end-pumped dual-wavelength Nd, Gd:YSGG laser

We demonstrate a dual-wavelength laser based on a new laser material-Nd, Gd:YSGG, or Nd:GYSGG for short-for the first time to our knowledge. Besides its attractive properties such as antiradiation, high segregation coefficient, etc., this kind of laser crystal also shows excellent laser performance. For continuous-wave operation, the maximum output power is 10.1 W with the absorbed power of 18.45 W at 808 nm, corresponding to the slope efficiency of nearly 60%. The maximum single pulse energy and peak power reach 277 μJ and 4.6 kW (60 ns) when the absorbed pump power is 11.4 W for acousto-optic Q-switched operation.

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.

Growth and Luminescence of M-Type

M-type GdTaO₄ and Tb:GdTaO₄ bulk single crystals were first grown by Czochralski method. Transmission, excitation, emission spectra and luminescence decay curves of them were measured. The refractive indices of GdTaO₄ were calculated with its transmission spectrum and fitted with Sellmeier equation. GdTaO₄ shows Gd³⁺ absorption and defect luminescence, Tb³⁺ exhibits its typical absorption and luminescence in GdTaO₄. The luminescence decay times of GdTaO₄ and Tb:GdTaO₄ were also determined by fitting luminescence decay curves with single-exponential function.

{\rm GdTaO}_{4}

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.

and Tb:

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.

{\rm GdTaO}_{4}

The structure of the melt near a crystal–melt interface is a fundamental problem in the dynamics of crystal growth. In this work, high-temperature Raman spectroscopy was applied to investigate in situ the structure of the melt near the α-BaB2O4 (α-BBO) crystal–melt interface. A structured melt was found in this region: (B3O6)3− groups form near the interface and vanish towards the bulk melt. The crystal growth habit was then explained by the periodic bond chain (PBC) theory. At the α-BBO crystal–melt interface, the growth units, namely the (B3O6)3− anion groups and Ba2+ cations, stack mainly along four types of PBCs. These four PBCs constitute three potential F faces: {10\bar{1} 2}, {01\bar{1} 4} and {10\bar{1} 10}. The predicted results are in good agreement with the observed growth habit of α-BBO crystal.

Scintillation Single Crystals

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.

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

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.