Qiguang Tan

2.0W diode-pumped Er:Yb:YAl3(BO3)4 laser at 1.5–1.6μm

An efficient and high output power laser has been realized for an Er:Yb:YAl3(BO3)4 crystal end pumped by a 970nm diode laser. Under the absorbed pump power of 15.5W, quasi-continuous-wave output power of 2.0W at 1.5–1.6μm has been obtained in a hemispherical cavity. The laser had an absorbed pump threshold power of 4.7W and a slope efficiency of 21%. The influence of the laser output power and output coupler transmission on the output laser spectra has also been investigated.

Radiative-trapping and fluorescence-concentration quenching effects of Yb:YAl 3 (BO 3 ) 4 crystals

The effects of radiative-trapping and fluorescence-concentration quenching on the emission spectra and fluorescence lifetimes of Yb3+-doped YAl3(BO3)4 crystals with a series of Yb3+ concentrations were studied. The shift of barycenters in emission spectra, Δλ, was proposed as an appraisement of the radiative-trapping effect on the spectra, and an empirical relation between Δλ and Yb3+ concentration in the Yb:YAl3(BO3)4 crystals was deduced. The model of excitation random walk was used to analyze the effects of radiative trapping and concentration quenching on the fluorescence lifetimes. The relation between fluorescence lifetime and Yb3+ concentration was obtained.

Energy transfer in Yb3+-Er3+-codoped bismuth borate glasses

The mechanism of energy transfer from Yb3+ to Er3+ ions has been studied in bismuth borate glasses with a serial Yb3+ concentration. The analysis of the donor fluorescence decay with a low concentration has been used to determine the multipole character of the energy transfer. The energy-transfer microparameters were determined and used to calculate the migration-assisted energy-transfer rates on the basis of the hopping model, which are in agreement with those obtained by fitting the fluorescence decay curves. An efficient energy transfer from Yb3+:2F5/2 to Er3+:I11/2 in the bismuth borate glasses has been demonstrated.

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

Detailed polarized spectral properties of a 3.6 at. % 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 3.6 at. % 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.

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%.

Laser emission from unprocessed cleavage microchip

A method utilizing an unprocessed cleavage microchip as the solid-state laser gain medium is proposed. Pumped by a Ti:sapphire laser at 871 nm, 1060 nm continuous-wave laser emission with slope efficiency of 23% has been achieved in an unprocessed microchip directly obtained from a cleavage Nd3+:LaB3O6 crystal. Based on this method, it is possible to avoid the difficulty of the microchip gain medium processing and largely lower the cost of solid-state lasers.

Spectroscopic properties of Pr3+ ions in biaxial LaB3O6 crystal

LaB3O6 single crystal doped with Pr3+ ions has been grown by the Czochralski method. The angular relationship between the principal axes of the optical indicatrix and the crystallographic axes in the crystal was determined. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves of the crystal were measured at room temperature. The modified Judd-Ofelt theories, extended to the anisotropic crystal, have been applied to analyze the spectra. The spectroscopic parameters, including the Judd-Ofelt intensity parameters Ωt,q(t=2,4,6), spontaneous emission probabilities, fluorescence branching ratios, radiative lifetimes, fluorescence quantum efficiencies, and stimulated emission cross sections were calculated and analyzed. The promising luminescent and upper laser level of the Pr3+:LaB3O6 crystal is determined.

Highly efficient Nd3+:LaB3O6 cleavage microchip laser

The improvement of the laser performances of an unprocessed 5.6at.% Nd3+:LaB3O6 cleavage microchip has been reported. Pumped by a Ti:sapphire laser at 871nm, quasi-cw output laser power up to 395mW around 1060nm wavelength with slope efficiency near 52% has been obtained in an end-pumped plano-plano resonator. The influence of the ratio between the cavity mode and pump beam area on the laser performances and laser spectra at various output powers has been investigated. The experimental results have shown that the cleavage technique can become a practical and effective method to obtain the microchip laser medium easily and directly.

Polarized spectral characteristics of Nd3+ : KY(MoO4)(2) crystal with perfect cleavage planes: a promising microchip gain medium

An Nd3+:KY(MoO4)2 crystal with perfect cleavage planes was grown by the Czochralski method. The room-temperature polarized absorption and the infrared-emission and upconversion visible-emission characteristics of the crystal were investigated. The comparison between the radiative and fluorescence lifetimes showed that the nonradiative transition from the 4F3/2 multiplet is nearly neglectable for the crystal. The relation among the crystal structure, the spectroscopic parameters, and the laser performances of the crystal were discussed. The cleavage nature and good spectral properties of the Nd3+:KY(MoO4)2 crystal show that it is a promising microchip gain medium.

Passively Q-switched laser operation of Nd:LaB3O6 cleavage microchip

Pumped by a Ti:sapphire laser, a passively Q-switched laser oscillation from an unprocessed Nd:LaB3O6 cleavage microchip with a Cr4+:YAG saturable absorber has been demonstrated. The influence of the transmission of the output coupler on the pulse width and repetition rate at various absorbed pump powers has been investigated. A pulse with 2.8μJ energy, 2.2ns duration, and 29kHz repetition rate at 1060nm was obtained at the absorbed pump power of 1.25W and output coupler transmission of 3.2%, which results in 1.25kW peak power. The polarization and spectral properties of laser radiation were measured.