Polarized spectroscopic properties of Ho ions in NaLa(MoO4)2 crystal

A Ho³⁺-doped NaLa(MoO₄)₂ single crystal was grown by the Czochralski method. The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves of the crystal were measured at room temperature. The spontaneous emission probabilities, radiative lifetimes, and fluorescence branching ratios of the typical fluorescence multiplets of Ho³⁺ ions were calculated. The polarized stimulated emission and gain cross-sections of the ⁵I₇ → ⁵I₈ transition were obtained. The results show that the Ho³⁺:NaLa(MoO₄)₂ crystal is a promising gain medium for tunable and ultrashort pulse lasers operating around 2.0 μm.     

Growth and spectral properties of Cr:KAl(MoO4)2 crystal

The Cr³⁺:KAl(MoO₄)₂ single crystal was grown by top seeding solution growth method (TSSG). Based on the absorption and emission spectra, the crystal field strength Dq, the Racah parameters B and C, the effective phonon energy ?ω and the Huang-Rhys factor S were calculated: Dq = 1494.8 cm^− 1, B = 585.5 cm^− 1 and C = 3049 cm^− 1, ?ω = 373.8 cm^− 1 and the Huang-Rhys factor S = 3.74, respectively. The value Dq/B = 2.55 indicates that Cr³⁺ ion occupies the strong crystal field site in KAl(MoO₄)₂ crystal. A comparison of crystal field parameters for Cr³⁺:KAl(MoO₄)₂ with other Cr³⁺-doped crystals was presented. The results of spectral measurement show that Cr³⁺:KAl(MoO₄)₂ may be a potential candidate for broadband laser applications.     

Nd:NaBi(WO4)2晶体光谱性能研究

采用提拉法生长出了四方晶系白钨矿结构的掺钕钨酸铋钠[分子式Nd:NaBi(WO4)2,简称Nd:NBW]晶体.通过TG-DTA分析得到晶体的熔点为936.2℃,从XRD分析得到晶胞参数a=b=0.5275nm,c=1.1493nm.测试了该晶体的红外光谱和拉曼光谱,讨论了晶体的振动归属.由吸收光谱可以看出,该晶体在802nm有较强的吸收峰,半峰宽约16nm,并计算了晶体中Nd3 的吸收截面积.     

Polarized spectral properties of Tm:K5Bi(MoO4)4 crystal

Trivalent thulium-doped K₅Bi(MoO₄)₄ single crystals were grown by the Czochralski method. Its polarized absorption and fluorescence spectra and fluorescence decay curves were recorded at room temperature. On the basis of the Judd-Ofelt theory, the spectral parameters of the Tm³⁺:K₅Bi(MoO₄)₄ crystal were calculated. The cross relaxations between Tm³⁺ ions were analyzed. The emission cross sections of the ³F₄ → ³H₆ transition were obtained by the Fuchtbauer-Ladenburg formula and then the gain cross sections around 1.9 μm were calculated. The peak emission cross section and width of emission band around 1.9 μm are comparable to those for Tm³⁺:YAG and the tunable range is about 280 nm for the potential ∼1.9 μm laser operation via the ³F₄ → ³H₆ transition.     

Ca4REO(BO3)3 crystals for green and blue microchip laser generation: from crystal growth to laser and nonlinear optical properties

We have taken advantage of congruent melting behavior of the nonlinear rare-earth oxoborate Ca₄REO(BO₃)₃ family to perfect a process of collective fabrication of self-frequency doubling microchip laser based on Nd:GdCOB (Ca₄Gd_1−xNd_xO(BO₃)₃) crystals. The process goes from Czochralski boule to 1 × 3 mm² chips perfectly oriented (better than 0.1°) to the phase matching direction (θ=90°, φ=46°) in the XY principal plane, with dielectric mirrors directly deposited on both faces of the chips. 20 mW of self-frequency doubling output power at 530 nm was performed under 800 mW of diode laser as incident pump power at 812 nm. In addition, new compositions from the solid solution Ca₄Gd_1−xY_xO(BO₃)₃ (Gd_1−xY_xCOB) (x=0.13, 0.16, 0.44) have been grown by the Czochralski pulling method, in order to achieve noncritical phase matching (NCPM) second harmonic generation of ⁴F_3/2 → ⁴I_9/2 Nd³⁺ doped laser hosts. Three types of laser wavelengths have been chosen: Nd:YAP (YAlO₃) at 930 nm, Nd:YAG (Y₃Al₅O₁₂) at 946 nm, and Nd:ASL (Nd_ySr_1−x La_x−yMg_x Al_12−xO₁₉) at 900 nm. Angular acceptance measurements of these three types of compositions present very large values, compared to pure GdCOB or YCOB oriented in critical phase matching configurations.     

Sub-nanosecond Nd:Lu0.61Gd0.39VO4 microchip laser

We report the fabrication and operation of a single-to-three-mode, sub-nanosecond passively Q-switched Nd:Lu_0.61Gd_0.39VO₄/Cr⁴⁺:YAG microchip laser, which exhibits changes in mode structure with increasing incident pump power. The laser exhibits longitudinal mode oscillations with a partial transverse mode overlap. The shortest pulse duration, highest pulse energy and peak power observed are 646 ps, 8.7 μJ and 13.5 kW, respectively.     

Spectral parameters of Nd3+ ion in Nd:KLa(WO4)2 crystal

The spectral parameters of Nd³⁺ ions in Nd:KLa(WO₄)₂ crystal have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the parameters of oscillator strengths are Ω₂=3.0887×10^–20 cm², Ω₄=1.0375×10^–20 cm², Ω₆=1.0422×10^–20 cm², the radiative lifetime is 685 μs, the quantum efficiency is 30.7%, and the fluorescence branch ratios were calculated: β₁=0.432, β₂=0.475, β₃=0.089, β₄=0.004. Electronic Publication     

Nd:Gd_xY_(1-x)Ca_4O(BO_3)_3晶体的生长及其光谱性能研究

利用熔体提拉法生长了大尺寸,高质量的新型激光自信频晶体Ｎｄ：ＧｄｘＹ１－ｘＣａ４Ｏ（ＢＯ３）３简称Ｎｄ：ＧｄＹＣＯＢ）．对Ｎｄ：ＧｄＹＣＯＢ晶体的ＸＲＤ衍射图进行指标化,得到它的晶胞参数为α＝８．０８０Ａ; ｂ＝１６．０１６Ａ; ｃ＝３．５３８Ａ; β＝１０１．１８°;μ＝４９１．１Ａ３．对取自不同部位的晶体粉末进行ＩＣＰ原子发射光谱分析表明晶体整体组份均匀一致,根据熔体和晶体粉末的ＩＣＰ数据计算,Ｎｄ：ＧｄＹＣＯＢ晶体中Ｎｄ３＋的分凝系数为０．６３．首次报道了 Ｎｄ：ＧｄＹＣＯＢ晶体２００～３０００ｎｍ室温透过光谱和室温荧光光谱及荧光寿命．室温透过光谱表明Ｎｄ：ＧｄＹＣＯＢ晶体的紫外吸收边在～２２０ｎｍ,具有很宽的透光波段（～２２０～２７００ｎｍ）; Ｎｄ：ＧｄＹＣＯＢ晶体在８００ｎｍ附近存在很强的吸收,适合于ＬＤ泵浦．荧光光谱表明Ｎｄ：ＧｄＹＣＯＢ晶体是一种很有潜力的ＲＧＢ（ｒｅｄ;ｇｒｅｅｎ, ｂｌｕｅ）激光自信频晶体．掺杂 ４％、 ５％ Ｎｄ：ＧｄＹＣＯＢ晶体的荧光寿命分别为 １０５μｓ和１００μｓ．     

Self-assembled 3D flower-like NaY(MoO4)2:Eu microarchitectures: Hydrothermal synthesis, formation mechanism and luminescence properties

Self-assembled 3D flower-like NaY(MoO₄)₂:Eu³⁺ microarchitectures were successfully synthesized by a glycine-assisted hydrothermal method at 180 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) were employed to characterize the as-obtained products. It was found that morphology modulation could be easily realized by changing the time of hydrothermal reaction system. 3D flower-like NaY(MoO₄)₂:Eu³⁺ microarchitectures were formed with 72 h reaction time. The formation mechanism for flower-like architecture was proposed on the basis of a series of time-dependent experiments. The NaY(MoO₄)₂:Eu³⁺ powders obtained can be effectively excited by 396 nm light, and exhibit strong red emission around 615 nm, attributed to the Eu³⁺⁵D₀ → ⁷F₂ transition. An investigation on the photoluminescence (PL) properties of NaY(MoO₄)₂:Eu³⁺ obtained revealed that the luminescence properties were correlated with the morphology and size.     

Passive mode-locking of diode-pumped Nd:GdVO4 laser with carbon nanotube intracavity absorber

By using single-walled carbon nanotubes as the saturable absorber fabricated by a vertical evaporation method, passive mode-locking of a Nd:GdVO₄ laser was realized in a W-type folded cavity. The laser generated 8?ps pulses at a repetition rate of 81?MHz. At 10.4?W of the incident pump power, average output power of 1.22?W was achieved and the corresponding peak power and energy of a single pulse were 1.88?kW and 15?nJ, respectively.     

Growth and spectral properties of Er:NaGd(WO4)2 crystal

A high optical quality Er³⁺-doped NaGd(WO₄)₂ single crystal with dimensions of ∅18 × 50 mm³ has been grown using the Czochralski method. The structure of the grown crystal was proved by X-ray powder diffraction. The accurate concentration of Er³⁺ ion in the crystal was measured. The absorption spectra, fluorescence spectra and fluorescence lifetime of the crystal were measured at room temperature. Green up-conversion luminescence has been observed when the crystal is excited at 965 nm.     

Effect of Calcium on Nd:GdVO4 single crystal

The Ca_0.08Gd_0.92VO₄ crystal and Nd-doped Ca_0.08Gd_0.92VO₄ crystals were grown by the Czochralski method; the lattice parameters of the crystals were determined by XRD. The results showed that substituting Nd³⁺ caused an increase in lattice parameter; the segregation coefficient of Nd³⁺ ions in the crystal is lower than that of Nd:GdVO₄ crystal; the absorption spectra, fluorescence spectra, absorption cross-section and the emission cross-section of the Nd:Ca_0.08Gd_0.92VO₄ crystal were investigated at room temperature; furthermore, the Raman performance of Ca_0.08Gd_0.92VO₄ crystal was improved.     

The characteristics of Kerr lens mode-locked Nd:YVO4 laser with a symmetrical z-shaped cavity

In this paper, a diode-pumped CW Kerr lens mode-locked Nd:YVO₄ laser is demonstrated in the megahertz (MHz) oscillations mode-locked regime for the first time. Considered the beam mode size in the laser crystal and the Kerr lens sensitivity, an effective laser system with a symmetrical z-shaped cavity is strictly designed by the ABCD matrix and experimentally researched. The laser system can be self-starting without the need of any additional components. When an incident pump power is of 8 W, the maximum output power is 1.65 W, with a slope efficiency of 23.8%. The mode-locked repetition rate and pulse width are 530 MHz and 15.1 ps, respectively.     

Diode-pumped efficient laser operation and spectroscopy of Tm,Ho:YVO4

Spectroscopic characterization of co-doped Tm,Ho:YVO₄ crystal grown by the Czochralski method has been performed including absorption spectrum, emitting spectrum and luminescence decay lifetime. The polarization emitting spectrum around 2 μm is accomplished by exciting a singly Ho³⁺ doped YVO₄ crystal to exclude the influence of Tm³⁺³F₄-³H₆ transition and the emission cross section is deduced from both Fuchtbauer-Ladenburg (F-L) equation and reciprocity method (RM). In addition, we report up to 10.4 W continuous wave (CW) output with a conversion efficiency of 40% and 10.3 W Q-Switch output with 12.5 kHz pulse repetition rate of diode-pumped cryogenic Tm,Ho:YVO₄ laser. For Q-Switch operation, the minimum pulse width of 28.2 ns is obtained, all of which demonstrate that the Tm,Ho:YVO₄ is excellent laser material for 2 μm radiation.     

Diode-pumped doubly Q-switched mode-locked YVO4/Nd:YVO4/KTP green laser with AO and GaAs saturable absorber

By using both acousto-optic modulator and GaAs saturable absorber, a diode-pumped Q-switched and mode-locked(QML) YVO₄/Nd:YVO₄/KTP green laser is presented. The experimental results show that the doubly QML YVO₄/Nd:YVO₄/KTP green laser has good stability and nearly 100% modulation depth. The average output power and the pulse width of the Q-switched envelope have been measured. The mode-locked pulse inside the Q-switched envelope has a repetition rate of 137 MHz and its pulse width is estimated to be about 280 ps. By using a hyperbolic secant square function and considering the Gaussian distribution of the intracavity photon density, the coupled equations for diode-pumped dual-loss-modulated QML green laser is given and the numerical solutions of the equations are in good agreement with the experimental results.     

Radiation damage study of MeV ions-implanted Nd:YVO4 crystal

Damage formation mechanism of Nd:YVO₄ implanted with MeV ions is investigated. MeV Si⁺ ions were implanted into Nd:YVO₄ crystal, and the lattice damage was measured using Rutherford backscattering spectroscopy/channeling (RBS/C) method. The damage creation kinetic indicates a significant contribution from electronic energy loss to the surface damage. A detailed analysis allows us to deduce the different contributions from electronic and nuclear stopping powers to the lattice damage production. An obvious difference in extent of damage from 1 MeV and 3 MeV Si⁺ implantations also implies that there exists a threshold value of the electronic energy deposition for damage formation. The exact value of threshold is obtained by comparison with the experimental data obtained from 3 MeV O⁺, F⁺ and Si⁺ implantation results, which turns out to be (1.7 ± 0.1) keV/nm.     

Enhancement of stability and peak power in a diode-pumped doubly QML YVO4/Nd:YVO4 laser with EO and Cr:YAG saturable absorber

A diode-pumped doubly Q-switched and mode-locked (QML) YVO₄/NdYVO₄ laser is realized with the electro-optic (EO) modulator and Cr⁴⁺:YAG saturable absorber, in which the repetition rate of the Q-switched envelope is controlled by the active EO modulation while the mode-locked pulses inside the Q-switched envelope depend on both the actively modulated loss and the passive saturable absorption. The experimental results show that the doubly QML laser can generate more stable and shorter pulses with higher peak power when compared with the singly passively QML laser with Cr⁴⁺:YAG. At the pump power of 20 W and the repetition rate 1 kHz, a 21 ns Q-switched pulse envelope with a average mode-locked peak power of 544 kW is obtained, which is the shortest Q-switched pulse envelope to my knowledge. In comparison to the singly passively QML laser with Cr⁴⁺:YAG, the doubly QML laser has compressed the Q-switched envelope pulse width 70% and improved the mode-locked pulsed peak power 27 times. By using a hyperbolic secant square function and considering the Gaussian distribution of the intracavity photon density, the coupled equations for diode-pumped dual-loss-modulated QML laser is given and the numerical solutions of the equations are in good agreement with the experimental results.     

Mg(BH4)2-NaNH2体系的加热放氢性能研究

采用机械球磨法制备了Mg(BH4)2-NaNH2复合储氢材料,研究了Mg(BH4)2和NaNH2之间的相互作用及其加热放氢性能。当物质的量比为1∶2时,Mg(BH4)2与NaNH2之间发生反应:Mg(BH4)2+2NaNH2→2NaBH4+Mg(NH2)2。当物质的量比为1∶1时,Mg(BH4)2与NaNH2之间发生反应:Mg(BH4)2+NaNH2→NaBH4+MgBNH6。加热到400℃,该样品分两步进行放氢反应,放氢峰温分别在190℃和369℃,可以放出4.7%(质量分数)氢气。第一步放氢反应为MgBNH6分解产生MgH2,即:MgBNH6→MgH2+BN+2H2。第二步放氢反应为MgH2的分解:MgH2→Mg+H2。     

Spectral characterizations of Nd3+:KLa(WO4)2 crystal

The absorption and emission of Nd³⁺:KLa(WO₄)₂ crystal were investigated. The uniaxial crystal Nd³⁺:KLa(WO₄)₂ shows strong polarization dependence. The intensity of the absorption bands in E//c is about four times than that in E//a. The absorption cross section σ_a is 22.6 × 10^–20 cm² for E//c. The emission cross section at 1.069 μm is 2.09 × 10^–19 cm². The fluorescence lifetime is 157 μs at 300 K. The relationship of Nd³⁺ concentrations with fluorescence intensity and lifetime was discussed. The results show the ca 3 at % Nd³⁺ concentration in Nd³⁺:KLa(WO₄)₂ crystal is appropriate. Electronic Publication