C. Y. Tu

Spectroscopy of GdAl3(BO3)4: Tm3+ crystal

Tm{sup 3+}:GdAl{sub 3}(BO{sub 3}){sub 4} crystals were grown successfully from K{sub 2}Mo{sub 3}O{sub 10}-B{sub 2}O{sub 3} solvent by using the top seeded solution growth method. The absorption spectra for both {sigma} and {pi} polarizations were presented. The Judd-Ofelt (J-O) intensity parameters were found to be {omega}{sub 2}=4.54x10{sup -20} cm{sup 2}, {omega}{sub 4}=2.25x10{sup -20} cm{sup 2}, and {omega}{sub 6}=3.39x10{sup -20} cm{sup 2}. The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetime as well as the branching ratios were calculated. Unpolarized and polarized emission spectra were obtained under the excitations of 468 and 797 nm, respectively. This crystal may be preferable for GaAlAs laser pumping.Tm3+:GdAl3(BO3)4 crystals were grown successfully from K2Mo3O10-B2O3 solvent by using the top seeded solution growth method. The absorption spectra for both σ and π polarizations were presented. The Judd-Ofelt (J-O) intensity parameters were found to be Ω2=4.54×10−20cm2,Ω4=2.25×10−20cm2, and Ω6=3.39×10−20cm2. The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetime as well as the branching ratios were calculated. Unpolarized and polarized emission spectra were obtained under the excitations of 468 and 797 nm, respectively. This crystal may be preferable for GaAlAs laser pumping.

End-pumped Tm,Ho:NaY(WO4)2 crystal laser at 2.07 μm

We presented an infrared laser output at 2.07 μm with Tm,Ho:NaY(WO4)2 crystal end-pumped by 795 nm laser diode at room temperature. The crystal was grown by the Czochralski method with the concentrations of 5 at % Tm3+ and 1 at % Ho3+. The highest output power was up to 2.7 W corresponding to the crystal temperature being controlled at 283 K. The overall optical conversion efficiency was 5.4% and the slop efficiency was 26%. The output characteristics and the laser threshold affected by the pulse duration and temperature have been studied. We found the stability of the output power was correlative with the crystal temperature heavily. In addition, the wider pulse duration of pump could promote the output power efficiently.

Growth, spectroscopic characteristics and laser potential of Yb3+:Ca3La2(BO3)4 crystal

Crystal of Yb3+-doped Ca3La2(BO3)4 has been grown by the Czochralski technique. The room temperature absorption and fluorescence spectra of the crystal have been investigated. The result showed that this crystal exhibits broad absorption and emission with the FWHM of 11 nm at 978 nm and 66 nm FWHM at 1025 nm, respectively. The stimulated emission cross-section of Yb3+ ions were calculated using the reciprocity method and Fuchtbauer-Ladenburg method, respectively. The room temperature fluorescence decay curves of 2F5/2 manifold of Yb3+ ions were recorded for both crystal and powder samples. The effect of radiation tapping on the spectroscopic properties is discussed. The result that the lifetime of the powder sample is shorter than that of the bulk sample demonstrates the existence of radiation trapping effect. The laser potentiality was also evaluated and the results show that this crystal is a good candidate for tunable and ultrashort pulse lasers.

The growth, thermal and nonlinear optical properties of single-crystal GdAl3(BO3)4

The nonlinear optical single-crystals GdAl3(BO3)4 (GAB), space group R32, were grown by the top-seed solution growth (TSSG) method. The thermal properties and the nonlinear optical characteristics have been investigated. The two principal coefficients of thermal expansion along (100) and (001) were measured to be 5.30 × 10−6, 1.88 × 10−5 K−1. The transmission spectrum was measured and the second-harmonic generation (SHG) was presented. By way of our designed cross superimposed laser crystal multiplier, the frequency doubling laser at wavelength 457.5 nm was measured to be 18.2 mW and the facular properties indicated the multiplier contributed to the improvement of the frequency doubling conversion efficiency.

Polarized spectroscopic characterization and energy transfer of Tm3+-, Ho3+-BaLaGa3O7: new promising 2.0 µm laser crystals

The growth, absorption spectra, fluorescence spectra and luminescence decay curves of Tm3+-, Ho3+-BaLaGa3O7 crystals are reported. The 3F4→3H6 and 5I7→5I8 IR transitions of the Tm3+-BaLaGa3O7 and Ho3+-BaLaGa3O7 crystals are broad emission bands at about 2.0 µm; the corresponding stimulated emission cross-sections were calculated by the Fuchtbauer–Ladenburg equation, respectively. Based on the Judd–Ofelt theory, we obtained three intensity parameters and a series of spectral parameters. The energy transfer parameters between the Tm and the Ho were also calculated. These results show that these crystals are promising as tunable infrared laser crystals for the 2.0 µm regions.

Spectroscopic properties of Ho3+ doped CaNb2O6 crystal

Abstract Results of the growth and annealing processes of Ho3+:CaNb2O6 crystal with high oxygen defects were reported. The spectroscopic properties of Ho3+:CaNb2O6 were also analysed, and the decay curves of the bulk and powder samples in correspondence with the emission 5I7→5I8 at 2·0 μm were recorded. The effects of radiative trapping on the final results were also indicated, and the final value of the fluorescence lifetimes of 5I7→5I8 transition is calculated to be 5·19 ms. CaNb2O6 crystal was shown to be a prospective material for an infrared laser medium at 2·0 μm.

Polarized spectral properties and potential application of large-size Nd3+:Ba3Gd2(BO3)4 crystal

The Nd3+-doped Ba3Gd2(BO3)4 crystal with high optical quality and large size is reported in this paper. The growing processes and characteristics of Nd3+:Ba3Gd2(BO3)4 crystal are discussed. The absorption and luminescence spectra of Nd3+ in Ba3Gd2(BO3)4 crystal were measured at room temperature. The luminescence decay curve in correspondence with the 4F3/2 →4I11/2 transition centered at 1062 nm was also measured. The JO intensity parameters Ωt (t = 2,4,6) were calculated to be Ω2 = 1.263, Ω4 = 2.496, Ω6 = 3.606. The radiative lifetime τr and fluorescence lifetime τf are 317.771 and 115 μs respectively, and the fluorescence quantum efficiency is 37.1%.

1180 nm Raman laser operation of end-pumping Nd:GdAl3(BO3)4/SrWO4 crystal

We present an end-pumped continuous-wave Raman laser at 1180 nm with a 60 mm long pure crystal SrWO4 and an Nd:GdAl3(BO3)4 crystal. The highest output power Raman laser at 1180 nm is 15.5 mW corresponding to the pump power of 1.75 W. Results indicate that the intense self-doubling frequency effect of GdAl3(BO3)4 reduces the 1180 nm Raman laser output.