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.     

Crystal growth and spectral properties of Pr:La2(WO4)3

Pr³⁺-doped La₂(WO₄)₃ single crystal with dimensions up to Ø 20 mm × 35 mm has been grown by the Czochralski method. The structure of the Pr³⁺:La₂(WO₄)₃ crystal was determined by the X-ray powder diffraction and the Pr³⁺ concentration in this crystal was determined. The absorption and fluorescence spectra of Pr³⁺:La₂(WO₄)₃ crystal were measured at room temperature, and the fluorescence lifetime of main emission multiplets were estimated from the recorded decay curves. The spectral properties related to laser performance of the crystal were evaluated.     

Nd:GdxY1-xCa4O(BO3)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倍频晶体Nd:GdxY1-x(Ca4O(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a=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 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泵汪,为光光谱表明Nd:GdYCOB晶体是一种很有潜力的RGB（red,green,blue)激光自倍频晶体,掺杂4％,5％ Nd:GdYCOB晶体的荧光寿命分别为105us和100us。     

Preparation, mechanical properties and corrosion behaviors of oriented Ca(PO3)2 glass–ceramics

Highly oriented Ca(PO₃)₂ glass–ceramics were prepared by interface-induced nucleation. A polycrystalline Al₂O₃ plate was inserted into the Ca(PO₃)₂ glass melt. The crystallographic c-axis of most crystals were oriented in the direction perpendicular to the surface of Al₂O₃plate. The strongly oriented glass–ceramics showed notable anisotropic properties. The anisotropic mechanical properties were studied by Vickers microhardness test and the influence of crystal alignment on corrosion behaviors in simulated body fluid (SBF) was investigated by measuring and comparing the changes of surface roughness from 3D surface topography, using a confocal laser scanning microscopy (CLSM). The experimental results revealed that the measured hardness of two different crystal alignment directions showed the indentation size effect (ISE), the true hardness on the sample cut parallel to the Al₂O₃ plate was 500 MPa larger in comparison to the one cut perpendicular to the Al₂O₃ plate. During immersion in SBF for 12 days, the crystal aligned parallel was easier to be attacked by solution, and had a more rough surface than the crystal aligned perpendicularly.     

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.     

Multi-wavelength continuous-wave laser operation of Yb:Ca3Gd2(BO3)4 disordered crystal

The diode-pumped multi-wavelength continuous-wave laser operation of the disordered Yb:Ca₃Gd₂(BO₃)₄ crystal was firstly investigated in this paper. The simultaneous emission wavelengths varied from 2 to 5 in the range from 1045.4 to 1063.6 nm with the change of the absorbed pump power and crystal length. An output power of 1.4 W was obtained with four-wavelength emission, corresponding to an optical-optical slope efficiency of 23.7%. Five-wavelength emission at 1049.4, 1051.3, 1053.4, 1055.6 and 1057.4 nm was realized under the output power of 1.0 W. The absorption behavior of Yb:Ca₃Gd₂(BO₃)₄ have also been measured.     

Investigation of Nd ions spectroscopic and laser properties in SrF2 fluoride single crystal

The laser properties of SrF₂:Nd³⁺ crystal with neodymium ions concentration of 0.5 at.% were investigated under diode laser pumping. Using temperature tuning of laser diode pumping wavelength two different lines centered at about 1037 nm and 1044 nm attributed to oscillation of different optical centers were obtained. The maximum lasing slope efficiency of 37% was obtained. The absorption and fluorescence spectra of different individual and clustered Nd³⁺ ions optical centers were observed depending on Nd³⁺ concentration. The lifetimes of the high symmetry L-centers were measured and found to be two orders of magnitude longer than that for clustered M-centers at room temperature. The lifetimes of M-centers at different temperatures were measured and microparameter of ion-ion interaction in Nd-pairs was determined.     

Nd-doped fluoride film grown on LiYF4 substrate by pulsed laser deposition

The realization of a monocrystalline nanofilm of Nd³⁺-doped fluoride on LiYF₄ substrates by pulsed laser deposition is reported. The film was obtained by laser ablation with 355 nm photons of a bulk LiYF₄ crystal doped with Nd³⁺ ions at 1.5% atomic concentration. The measurements of the sample thickness obtained by an in situ interferometric technique, and the film optical characteristics analyzed via laser induced fluorescence spectroscopy upon UV and IR excitation, are presented. Lifetime measurements of the fundamental Nd³⁺ ion transition in the film were also performed. All the results were compared with those obtained in a Nd³⁺:LiYF₄ bulk crystal. The emission spectra of the deposited film following IR excitation seem to indicate the obtained deposit is Nd³⁺:YF₃.     

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.     

KTiOPO4 and Cs2WO2Cl4: Two exceptional cases of do ion luminescence

The compound KTiOPO₄ shows an extremely short wavelength titanate emission (390 nm) which is quenched at about 100 K. This luminescence is discussed in terms of a self-trapped excition which becomes mobile at higher temperatures. Comparison with other titanates is made. The linear titanate chain in KTiOPO₄ must be rather covalent. In Cs₂WO₂Cl₄ we observed an extremely long wavelength tungstate emission. Comparison with related tungstates is made. In Cs₂WO₂Cl₄ the chlorotungstate group is completely isolated. The low quenching temperature of this luminescence has a different origin from that of KTiOPO₄.     

Development of TiSiN CVD process using TiCl4/SiH4/NH3 chemistry for ULSI anti-oxidation barrier applications

CVD-TiSiN may be promising material for O₂ diffusion-barrier films in ultra-large scale integrated (ULSI) circuit applications, especially for dynamic random-access memory (DRAM) capacitors. We developed a method for introducing Si into TiN, which is a common material used for diffusion-barrier films. TiSiN films were deposited by reacting TiCl₄, SiH₄, and NH₃ in a hot-wall CVD reactor. We measured TiSiN film deposition rates, composition, crystal structure, and resistivity as a function of SiH₄ partial pressure. Adding Si to TiN converts the TiN film structure from columnar grains to columnar-free structure films, thereby effectively removing the diffusion paths for O₂. The resistivity of TiSiN films was increased by adding SiH₄ to the reactant gas. With an increase in SiH₄ partial pressure up to P_SiH4=0.8 Torr, the resistivity gradually increased, but for P_SiH4=1.2 Torr, the phase present in the film was almost SiN and its resistivity jumped up. TiSiN film rapid thermal annealing was performed to evaluate the anti-oxidation performance at the temperature range from 400 to 600 °C in 100 Torr of O₂. For an increase the Si concentration up to 4.4 at.% improved anti-oxidation performance of TiSiN films. Flow modulation chemical vapor deposition (FMCVD) was used to create TiSiN films with low Cl concentration and improved anti-oxidation performance.     

Growth and characterization of non-linear optical crystal Cd3Zn3B4O12

Cd₃Zn₃B₄O₁₂ polycrystals were synthesized by solid-state and wet chemical reaction methods. Cd₃Zn₃B₄O₁₂ single crystals with millimeter grade were grown from the self-flux B₂O₃ (Cd:Zn:B = 1:1:1.5); and larger crystals were obtained from the PbO-0.85PbF₂ fluxes easily. As-grown crystals were characterized by differential scanning calorimetry and thermogravimetric, X-ray diffraction, infrared and Raman spectral analysis, respectively. The non-linear optical coefficient of the Cd₃Zn₃B₄O₁₂ crystal is 2.6 times as large as that of KH₂PO₄ crystal. Chemical etching shows that this crystal is very stable in neutral solution and not hygroscopic in air at room temperature.     

Intensity parameters of Tm doped Sc2O3 transparent ceramic laser material

This work is focused on spectral investigations of Tm³⁺ doped Sc₂O₃ transparent ceramic as potential material for diode-pumped solid-state laser emitting around 2 μm. In the context of the Judd-Ofelt (J-O) theory a series of spectroscopic parameters such as J-O intensity parameters, oscillator strengths, radiative transitions probabilities, and radiative lifetimes as well as branching ratios are evaluated. The gain cross-sections which lead to an estimation of the probable operating laser wavelength for the ³F₄ → ³H₆ Tm³⁺ laser transition were also calculated.     

Single step synthesis of Ce doped CaAl2O4 and CaAl4O7 systems

Both CaAl₂O₄ (CA2) and CaAl₄O₇ (CA4) oxide-systems possess monoclinic crystal structure. Herein, we have prepared CA2 and CA4 systems via single step combustion route. A good correlation is observed between calculated and the standard lattice parameters. Ce³⁺ ions were deliberately doped as extrinsic impurities in order to understand the crystal symmetry effects on the emission characteristics in the as-prepared matrices. Large red-shift was observed in CA4-emission spectrum despite of their same crystal structures. Possible reasons are discussed.     

Crystal growth and frequency conversion of BaMgF4 single crystal by temperature gradient technique

The BaMgF₄ single crystal was grown by the temperature gradient technique. Highly pure MgF₂ and BaF₂ powders were used as raw materials and CaF₂ single crystal was chosen as a seed to induce BaMgF₄ single crystal grow along 〈0 0 1〉 orientation. The short cut-off wavelength of BaMgF₄ single crystal was determined to be 130 nm which is consistent with the previously reported result. We realized second harmonic generation from 1064 nm to 532 nm laser, and 800 nm to 400 nm femtosecond laser in single domain BaMgF₄ by using birefringent phase matching. 355-nm-wavelength laser was produced by Sum-Frequency Generation from 1064-nm- and 532-nm-wavelength laser, which is the shortest coherent radiation obtained in the UV in the BaMgF₄ crystal.     

Absorption and emission of ErNbO4 powder

Visible and near infrared absorption and emission (488 nm excitation) characteristics of ErNbO₄ powder, which were prepared by calcining the Er₂O₃ (50 mol%) and Nb₂O₅ (50 mol%) powder mixture at 1100 and 1600 °C for different durations, have been investigated at room temperature. The absorption and emission characteristics of these calcined ErNbO₄ powder were summarized and discussed in comparison with those of Er₂O₃. Weak emission of Er₂O₃ relative to the calcined ErNbO₄ is mainly conducted with absorption difference at the excitation wavelength 488 nm. The obvious spectral changes from Er₂O₃ to calcined ErNbO₄ samples are related to an elevated-temperature-assisted phase transformation according to the solid-state chemical reaction equation: Er₂O₃ + Nb₂O₅ 2ErNbO₄, which results in the changes of the ion environment of Er³⁺ and hence changes of the Stark levels of Er³⁺. The further spectral change as the strengthened calcination results from the improvement of ErNbO₄ purity in the calcined mixture. The borders between two green transitions and between two near infrared transitions in the emission spectra of both calcined samples and Er₂O₃ were tentatively identified by referencing earlier reported emission spectra of the precipitated Z-cut VTE Er(2.0 mol%):LiNbO₃ crystal and the match relation between absorption and emission spectra of the ErNbO₄ powder. A comparison was performed on the spectra of calcined ErNbO₄ powder and those of VTE Er(2.0 mol%):LiNbO₃ crystals. The results allow to preliminarily deem the contribution of ErNbO₄ precipitates, generated inside these crystals by the VTE procedure, to the spectra of these crystals.     

硅酸镓镧晶体谐振器的高频振动分析

利用Mindlin板理论分析了硅酸镓镧晶体板强耦合的厚度剪切振动和弯曲振动，获得了硅酸镓镧晶体板高频振动的色散关系、频谱关系和振动模态位移图。数值计算结果表明，Mindlin板理论可以获得硅酸镓镧晶体板厚度剪切振动的一阶精确截止频率，无需修正系数。基于石英晶体谐振器设计晶片最佳长厚比的选取方法，确定了硅酸镓镧晶片的最佳尺寸，避免了厚度剪切振动模态和弯曲振动模态的强耦合。通过绘制硅酸镓镧晶体板在最佳尺寸时的各振动模态位移图，发现厚度剪切振动模态是主振模态，具有很好的能陷效应。Mindlin板理论在硅酸镓镧晶体板高频振动的应用分析可以指导硅酸镓镧晶体谐振器的实际研发。     

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.     

Growth and optical properties of Er,Yb:YAl3(BO3)4 crystal

Single crystal of erbium, ytterbium-codoped yttrium aluminum tetraborate Er,Yb:YAl₃(BO₃)₄(Er,Yb:YAB) has been grown by the flux method. The absorption spectrum in the visible and NIR regions of Er,Yb:YAl₃(BO₃)₄ crystal are measured at room temperature and fluorescence spectrum of Er,Yb:YAl₃(BO₃)₄ crystal are also measured at room temperature, excited by 976 nm laser. Not only the strong NIR emission peaks located at 1548 nm was observed, but also the visible up-conversion luminescence has been found. The specific heat of the Er/Yb:YAB crystal at room temperature is 0.81 J/g °C.     

Photoelectrochemical property of ZnFe2O4/TiO2 double-layered films

ZnFe₂O₄/TiO₂ double-layered films on indium-tin oxide (ITO) substrate were prepared by a dip-coating method, and the optical absorption and photocurrent of the as-prepared films were measured. In the double-layered films, the onset of fundamental absorption edge shifts to a longer wavelength, and even shifts to a longer wavelength than that of ZnFe₂O₄-only film as the ZnFe₂O₄ layer thickness increases. Application of the coupled photoanodes double-layered films composed of ZnFe₂O₄ and TiO₂ can obviously increase the photocurrent. It was found that the photocurrent density of ZnFe₂O₄/TiO₂ double-layered films first increased and then decreased with increasing the ZnFe₂O₄ layer thickness. A five-fold increase in the photocurrent density was obtained compared with TiO₂-only films under optimum condition.