Yidong Huang

Comparison of optical spectra of Nd3+ in NdAl3(BO3)4 (NAB), Nd:GdAl3(BO3)4 (NGAB) and Nd:Gd0.2Y0.8Al3(BO3)4 (NGYAB) crystals

A comparative study of the optical absorption and luminescence of crystals of NdAl3(BO3)4 (NAB), Nd:GdAl3(BO3)4 (NGAB) and Nd:Gd0.2Y0.8Al3(BO3)4 (NGYAB) is presented. The Judd-Ofelt theory is applied to the fitting of experimental absorption line strengths to obtain the intensity parameters Ωt (t = 2,4,6) with root mean square errors of 11.8%, 3.8% and 8.6% for NAB, NGAB and NGYAB respectively. The intensity parameters are used to calculate the radiative transition rates, branching ratios and radiative lifetimes of Nd3+ ions undergoing transitions from 4F3/2 to 4IJ manifolds. The relevant spectroscopic parameters for laser applications (quantum efficiency and emission cross section) are also estimated. The results are compared among the three samples and other borate crystals. It is concluded that NAB is a laser crystal with high gain and thus a promising candidate for microchip laser application, while NGAB (or NGYAB) can be used as an alternative to the celebrated nonlinear laser crystal NYAB.

Yellow-light generation of 5.7 W by intracavity doubling self-Raman laser of YVO 4 /Nd:YVO 4 composite

A high-power 588 nm light produced by an intracavity frequency-doubling acousto-optic Q-switched self-frequency Raman laser is reported. A 20-mm-long YVO(4)/Nd:YVO(4) composite crystal and a 15-mm-long LiB(3)O(5) (LBO) with noncritical phase-matching (theta=90 degrees , phi=0 degrees ) cut were adopted for efficient self-Raman laser operation and second-harmonic generation, respectively. By the optimizing the focus position of incident pump light and Q-switch repetition rate, yellow light with 5.7 W average power was generated under the pump power of 23.5 W, corresponding to the overall diode-yellow conversion efficiency of 24.2% and slope efficiency of 32%. The pulse width is about 16 ns, and the pulse energy is up to 95 microJ.

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.

Novel Garnet-Structure Ca2GdZr2(AlO4)3:Ce3+ Phosphor and Its Structural Tuning of Optical Properties

Aluminate garnet phosphors Ca2GdZr2(AlO4)3:Ce(3+) (CGZA:Ce(3+)) for solid-state white lighting sources are reported. The crystal structure and Mulliken bonding population of the CGZA:Ce(3+) have been analyzed. The larger 5d ((2)D) barycenter shift εc and smaller phenomenological parameter 10Dq of Ce(3+) in CGZA are related to the larger covalent character of Ce-O. The tuning spectral properties of the Ce(3+)-doped CGZA-based isostructural phosphors are presented. The splitting of cubic crystal field energy level (2)Eg in Ca2REZr2(AlO4)3:Ce(3+) (CREZA:Ce(3+)) (RE = Lu, Y, and Gd) increases as the radius of RE(3+) increases, and the splitting of (2)Eg may dominate the difference of spectroscopic red-shift D(A) in CREZA:Ce(3+). The splitting of the (2)Eg in CaGd2ZrSc(AlO4)3:Ce(3+) (CGZSA:Ce(3+)) phosphors increases seemly due to the decreasing of the covalent character of Ce-O. Thermal quenching properties of Ce(3+)-doped CGZA-based isostructural phosphors are also presented and analyzed. For CREZA:Ce(3+) phosphors, the increasing of the radius of RE(3+) results in an enhancement of thermal quenching. The quenching of CGZSA:Ce(3+) is obviously stronger mainly due to the smaller energy difference between the lowest 5d excited state and 4f ground state.

Spectroscopic analysis and laser performance of Tm3+ : NaGd(MoO4)2 crystal

Detailed polarized spectral properties of Tm3+ : NaGd(MoO4)2 crystal have been investigated. The room temperature absorption and fluorescence spectra were recorded. The fluorescence decay mechanisms of the 1G4 and 3H4 multiplets in Tm3+ : NaGd(MoO4)2 crystal were discussed. Room temperature quasi-cw 1.9 µm laser emission from the Ti : sapphire laser pumped Tm3+ : NaGd(MoO4)2 crystal has been demonstrated. The maximum output power of 170 mW has been achieved with a slope efficiency of 25%.

A CW blue laser emission by self-sum-frequency-mixing in Nd3+:GdAl3(BO3)4 crystal

In this paper, we report a CW blue laser emission by self-sum-frequency-mixing in NGAB crystal. 48 μW of 0.459 μm blue laser output power was obtained with the absorbed pump power of 0.99 W from a CW Ti:sapphire laser, and the threshold power is about 100 mW. The results indicate that the NGAB is also a promising candidate for a blue laser source by self-sum-frequency-mixing. The blue laser efficiency can be further improved by optimizing the device parameters.

Enhanced efficiency of Er:Yb:Ce:NaGd(WO 4 ) 2 laser at 1.5–1.6 μm by the introduction of high-doping Ce 3+ ions

By the introduction of high-doping Ce3+ ions, the upconversion fluorescence of Er3+ ions was reduced, and the energy-transfer efficiency from Yb3+ to Er3+ ions was enhanced significantly in Er:Yb:Ce:NaGd(WO4)2 crystals. End pumped by a diode laser at 970 nm in a hemispherical cavity, a 2.0 W quasi-cw laser at 1.5-1.6 microm with slope efficiency of 19% and absorbed pump threshold of 2.0 W was achieved in a 1.7-mm-thick c-cut Er:Yb:Ce:NaGd(WO4)2 crystal. The results show that the Er.:Yb:Ce:NaGd(WO4)2 crystal with high-doping Ce3+ ions is a potential gain medium for a low-threshold 1.5-1.6 microm laser.

Theoretical study on the laser performances of Nd 3+ :YAG and Nd 3+ :YVO4 under indirect and direct pumping

Based on the model of cw end-pumped four-level system, the laser performances of Nd3+:YAG and Nd3+:YVO4 under indirect and direct pumping Nd3+ ions into the upper laser level are compared. The model takes the effect of concentration-dependent fluorescence quenching into account and enables the optimization of Nd3+ lasers. The slope efficiencies for incident and absorbed pumping powers as well as the incident and absorbed pumping thresholds of Nd3+:YAG and Nd3+:YVO4 lasers under indirect and direct pumping are analyzed. When the slope efficiency for the incident pumping power and the incident pumping threshold are concerned, a simple criterion determining which sample is suitable for direct pumping is given; however, in the case of the slope efficiency for the absorbed pumping power and the absorbed pumping threshold, the direct pumping is always better than the indirect pumping.

High-efficiency intracavity Nd:YVO 4 \KTA optical parametric oscillator with 3.6 W output power at 1.53 μm

An efficient intracavity KTA optical parametric oscillator (OPO) driven by diode-end-pumped acousto-optical Q-switched Nd:YVO(4) laser is demonstrated. The mode mismatch between fundamental cavity and OPO cavity caused by the thermal lens effect in Nd:YVO(4) crystal as the pump power increased was studied. To lessen mode mismatch, a thermal lens-like cavity mirror made of plane BK7 glass induced by idler absorption was introduced into the OPO cavity. Under a diode pump power of 20 W, a maximum 1535nm light output power of 3.6 W was achieved at the pulse repetition rate of 60 kHz, corresponding to a diode-to-signal conversion efficiency of 18%. This is the highest efficiency reported for eye-safe laser based on intracavity OPO.

Polarized spectral properties and laser demonstration of Tm3+-doped LiGd(MoO4)(2) crystal

Trivalent thulium-doped LiGd(MoO4)2 single crystals have been grown by the Czochralski method. Room-temperature polarized absorption and fluorescence spectra of the crystals were analyzed. The fluorescence decay curves of the 1G4, 3H4, and 3F4 multiplets were measured, and the decay mechanisms of the 1G4 and 3H4 multiplets were discussed. Spectroscopic parameters related to the laser operation around 1.90 μm via the 3F4→3H6 transition have been evaluated. Finally, end-pumped by a Ti:sapphire laser at 795 nm, the room-temperature quasi-continuous wave 1.9 μm laser emission was demonstrated with a slope efficiency of 28%.