Haomiao Zhu

Growth, spectral properties, and laser demonstration of Yb3+:BaGd2(MoO4)4 cleavage crystal

Detailed polarized spectral properties of a 3.6u2009at.u2009% Yb3+:BaGd2(MoO4)4 (Yb3+:BGM) cleavage crystal grown by the Czochralski method have been investigated, including the absorption cross section, the emission cross-section, and the fluorescence lifetime. The evaluation of the laser potentiality shows that the Yb3+:BGM crystal is promising for tunable and ultrashort laser generations around 1 μm. The room temperature quasi-CW laser operation of an unprocessed 3.6u2009at.u2009% Yb3+:BGM cleavage plate has been demonstrated with diode pumping. The results indicate that the Yb3+:BGM crystal is a good candidate for microchip laser gain medium by cleavage technique.

Characterization of laser crystal Yb:CaYAlO 4

Yb:CaYAlO4 (Yb:CYA) crystals with good optical qualities have been grown by the Czochralski method. The detailed polarized spectral properties, including absorption and fluorescence, were investigated. The results reveal a broadband emission feature (FWHM=77u2009nm at σ polarization). The fluorescence lifetime has been measured using the powder concentration dilution method, and the intrinsic lifetime was found to be 426u2009μs. The thermal properties, including specific heat, thermal expansion, and thermal diffusion coefficients, have been investigated. The thermal conductivities were calculated to be 3.6 and 3.2u2009W/m/K along the a and c axes, respectively, at room temperature. The CW laser performances have been studied for both π and σ polarizations. The slope efficiencies of 55.4% and 41.4% were obtained for π- and σ-polarized operations, respectively. All the results show that Yb:CYA crystals should be excellent candidates as a laser medium for efficient and ultrafast lasers in the 1u2009μm region.

Spectral properties and efficient laser operation near 2.0 μm of Tm 3+ :BaGd 2 (MoO 4 ) 4 crystal

A 6.4 at. %Tm3+-doped BaGd2(MoO4)4 cleavage crystal was grown by the Czochralski method. Detailed spectral properties of this crystal were investigated, including the polarized absorption and emission spectra and the fluorescence decay. The maximum absorption cross section of the pump band is 3.5 cm×10−20 cm at 798 nm with a bandwidth of 8 nm, which means that this crystal is suitable for laser diode pumping. The Judd-Ofelt theory was used to calculate the radiative transition probabilities between multiplets. Pumped by a Ti:sapphire laser, the ~2.0 μm quasi-cw laser operation was performed using a cleaved 1.1 mm thick wafer of this crystal in a hemispherical cavity. The achieved highest slope efficiency was 51% with a 6.7% output coupler and the corresponding threshold was 31 mW. The results show that a Tm3+:BaGd2(MoO4)4 crystal is a promising candidate for ~2.0 μm microchip lasers.

Polarized spectral properties and laser demonstration of Nd 3+ :BaGd 2 (MoO 4 ) 4 cleavage crystal

Detailed spectral properties of Nd3+:BaGd2(MoO4)4 cleavage crystal have been studied. Laser operation of a cleaved 1.2 at.%Nd3+:BaGd2(MoO4)4 crystal pumped by a Ti:sapphire laser was demonstrated. The achieved highest slope efficiencies are 51% and 16% for a 1061 and 1337 nm laser, respectively. The corresponding thresholds are ∼3 and 45 mW, respectively. The results reveal that the cleaved Nd3+:BGM crystal has a high optical quality, good parallelism, and flatness and is a promising candidate for microchip laser gain media without processing.

Polarized spectral characterization and laser demonstration of Nd3+:Li2Gd4(MoO4)7 crystal

Detailed polarized spectral properties of Nd3+:Li2Gd4(MoO4)7 crystal grown by the Czochralski method have been investigated. The Judd-Ofelt intense parameters Ω2,4,6, the absorption and emission cross sections, and the branching ratios were calculated for each polarization of the main transitions. The large absorption cross section (16.6×10−20cm2 of π polarization) and broad absorption band (7nm of π polarization) around 804nm indicate that this crystal can be pumped efficiently by diode lasers. The broad emission bands from the F3∕24 multiplet show that the crystal is a promising medium for tunable and short pulse lasers. Pumped by a Ti:sapphire laser, the maximum 514mW quasi-cw laser output around 1060nm has been obtained with a 1.5% output couple, the threshold is 35mW, and the slope efficiency is 32%.

Polarized spectral properties of Yb3+: Li2Gd4(MoO4)(7) crystal: a candidate for tunable and ultrashort pulse lasers

Detailed polarized spectral properties of a 3.2 at.% Yb3+ : Li2Gd4(MoO4)(7) crystal, including absorption cross-section, emission cross-section, up-conversion spectrum and intrinsic fluorescence lifetime, were investigated. The laser potentiality was also evaluated and the results show that this crystal is a good candidate for tunable and ultrashort pulse lasers.

Efficient quasi-continuous-wave and passively Q-switched laser operation of a Nd3+: BaGd2(MoO4)(4) cleavage plate

Pumped by a Ti:sapphire laser at 807 nm, efficient quasi-cw and passively Q-switched laser operations have been realized from a 1.1 mm thick, 1.2 at. % Nd(3+):BaGd(2)(MoO(4))(4) cleavage plate in a plano-plano cavity. When the absorbed pump power was 1060 mW, the achieved maximum quasi-cw output power was 580 mW. The slope efficiency and absorbed pump threshold power were 60% and 50 mW, respectively. Using a Cr(4+):YAG crystal with an initial transmission of 85% as the saturable absorber, a pulse laser with 3.0 microJ energy, 30 ns duration, and 52 kHz repetition rate has been obtained when the absorbed pump power was 1060 mW. The polarization characteristic and laser spectra of both the quasi-cw and passively Q-switched lasers have been measured.

2.05 μm laser from free-processing Tm3+, Ho3+:BaGd2(MoO4)4 crystal

Polarized spectral properties relevant to the 2.0 μm laser of Ho3+ ions have been investigated for a cleaved Tm3+, Ho3+:BaGd2 (MoO4)4 crystal. A 1.04 mm-thick wafer was directly cleaved from a single crystal and used as a laser gain medium without any surface processing. End-pumped by a laser diode at 795 nm in a plano-concave cavity, a quasi-continuous-wave (quasi-CW) 2.05 μm laser was realized with a slope efficiency of 22%. This crystal is a good candidate for the gain medium of a low-cost and compact solid state Ho3+ laser.

Diode-pumped laser operation of segmented grown Yb3+ : YAl3(BO3)4/YAl3(BO3)4 composite

An Yb3+u2009:u2009YAl3(BO3)4/YAl3(BO3)4 composite is obtained by the segmented crystal growth method. Diode-pumped laser operation is demonstrated in the 2.0u2009mm thick, (0u20090u20091)-oriented composite with a 0.8u2009mm thick, 9.5u2009at% Yb3+u2009:u2009YAl3(BO3)4 crystal segment. Under the absorbed pump power of 11.9u2009W, quasi-continuous-wave output powers of 0.82u2009W with a slope efficiency of nearly 20% and of 0.3u2009W with a slope efficiency of 10.5% around 1040u2009nm are achieved in hemispherical and plano–plano cavities, respectively.