Infrared (1.2-1.6 mu m) luminescence in Yb, Cr : YAG with 940 nm diode pumping

Infrared (1.2-1.6 mum) luminescence in a yttrium aluminium garnet (YAG) crystal, co-doped with Yb (10 at.%) and Cr (0.05 at.%) ions, was investigated under CW laser diode pumping (lambda = 940 nm). The Cr4+ emission band was observed with its peak at 1.35 mum and measured to be about 6% with respect to Yb3+ IR luminescence (lambda = 1.03 mum). Analysis of the crystal absorption and luminescence spectra allows one to conclude that Yb3+-Cr4+ energy transfer is a mechanism responsible for the B-3(2)(T-3(2))-B-3(1)((3)A(2)) emission of Cr4+ ions. This crystal is promising as an efficient source of the near infrared emission. (C) 2004 Elsevier B.V. All rights reserved.

Infrared (1.2-1.6 mu m) luminescence in Cr4+: Yb3Al5O12 single crystal with 940 nm diode pumping

Infrared (1.2-1.6 mu m) luminescence in a ytterbium aluminium garnet (YbAG) crystal, doped with Cr (0.05 at.%) ions, was investigated under CW laser diode pumping (lambda = 940 nm). The Cr4+ emission band was observed with its peak at 1.34 mu m and measured to be about 1.3 times with respect to Yb3+ IR luminescence (lambda = 1.03 mu m). We demonstrate that for the excitation wavelength of 940 nm Yb3+ ions act as sensitizers of the B-3(2)(T-3(2))-B-3(1)((3)A(2)) emission of Cr4+ ions. This crystal is promising as a high-efficient system for tunable laser (1.2-1.6 mu m) output. (c) 2004 Elsevier B.V. All rights reserved.

High Power 940 nm Al-free Active Region Laser Diodes and Bars with a Broad Waveguide

The 940 nm Al-free active region laser diodes and bars with a broad waveguide were designed and fabricated. The stuctures were grown by metal organic chemical vapour deposition. The devices show excellent performances. The maximum output power of 6.7 W in the 100 f^m broad-area laser diodes has been measured, and is 2. 5 times higher than that in the Al-containing active region laser diodes with a narrow waveguide and 1. 7 times higher than that in Al-free active region laser diodes with a narrow waveguide. The 19 % fill-factor laser diode bars emit 33 W, and they can operate at 15W with low degradation rates.

Instability Analysis of Nonlinear Surface Waves in a Circular Cylindrical Container Subjected to a Vertical Excitation

Singular perturbation theory of two-time scale expansions was developed both in inviscid and weak viscous fluids to investigate the motion of single surface standing wave in a liquid-filled circular cylindrical vessel, which is subject to a vertical periodical oscillation. Firstly, it is assumed that the fluid in the circular cylindrical vessel is inviscid, incompressible and the motion is irrotational, a nonlinear evolution equation of slowly varying complex amplitude, which incorporates cubic nonlinear term, external excitation and the influence of surface tension, was derived from solvability condition of high-order approximation. It shows that when forced frequency is low, the effect of surface tension on mode selection of surface wave is not important. However, when forced frequency is high, the influence of surface tension is significant, and can not be neglected. This proved that the surface tension has the function, which causes free surface returning to equilibrium location. Theoretical results much close to experimental results when the surface tension is considered. In fact, the damping will appear in actual physical system due to dissipation of viscosity of fluid. Based upon weakly viscous fluids assumption, the fluid field was divided into an outer potential flow region and an inner boundary layer region. A linear amplitude equation of slowly varying complex amplitude, which incorporates damping term and external excitation, was derived from linearized Navier-Stokes equation. The analytical expression of damping coefficient was determined and the relation between damping and other related parameters (such as viscosity, forced amplitude and depth of fluid) was presented. The nonlinear amplitude equation and a dispersion, which had been derived from the inviscid fluid approximation, were modified by adding linear damping. It was found that the modified results much reasonably close to experimental results. Moreover, the influence both of the surface tension and the weak viscosity on the mode formation was described by comparing theoretical and experimental results. The results show that when the forcing frequency is low, the viscosity of the fluid is prominent for the mode selection. However, when the forcing frequency is high, the surface tension of the fluid is prominent. Finally, instability of the surface wave is analyzed and properties of the solutions of the modified amplitude equation are determined together with phase-plane trajectories. A necessary condition of forming stable surface wave is obtained and unstable regions are illustrated. (c) 2005 Elsevier SAS. All rights reserved.

Hydrodynamic interaction between two vertical cylinders in water waves

The hydrodynamic interaction between two vertical cylinders in water waves is investigated based on the linearized potential flow theory. One of the two cylinders is fixed at the bottom while the other is articulated at the bottom and oscillates with small amplitudes in the direction of the incident wave. Both the diffracted wave and the radiation wave are studied in the present paper. A simple analytical expression for the velocity potential on the surface of each cylinder is obtained by means of Graf's addition theorem. The wave-excited forces and moments on the cylinders, the added masses and the radiation damping coefficients of the oscillating cylinder are all expressed explicitly in series form. The coefficients of the series are determined by solving algebraic equations. Several numerical examples are given to illustrate the effects of various parameters, such as the separation distance, the relative size of the cylinders, and the incident angle, on the first-order and steady second-order forces, the added masses and radiation-damping coefficients as well as the response of the oscillating cylinder.

岩石圈板块的统一运动规律

<正> 岩石圈板块的运动规律对于研究板块的驱动机理具有十分重要的意义,它一直吸引着地球科学家的注意,文献[1]和[2]曾试图利用统计图表的方法,找出板块运动速度分别与板块的总面积、大陆面积、洋脊长度、海沟长度和换转断层长度之间的关联。但是,都没有取得令人满意的规律性结果。

激光二极管抽运的国产Yb:YAG陶瓷激光器

研究了国产Yb:YAG陶瓷的激光输出特性。激光器采用激光二极管(LD)纵向同轴抽运Yb:YAG陶瓷样品,样品的掺杂原子数分数为1%,一端面镀940 nm和1030 nm双增透膜,另一端面镀1030 nm增透膜,激光器在1031 nm处获得了近红外激光输出。实验中分别测试了Yb:YAG陶瓷在不同输出透射率(T=4%,8%,10%)条件下的激光输出特性。整个实验过程中,激光器维持基横模运转。当输出透射率为10%,吸收的抽运功率为9 W时,激光器获得最大的激光输出功率为1.63 W,相应的斜率效率为23.2%。

Single attosecond pulse generation in He+ by controlling the instant ionization rate using attosecond pulse trains combined with an intense laser pulse

High-order harmonics and single attosecond pulse generation by using an infrared laser pulse combined with attosecond pulse trains (APT) interacting with He+ have been investigated. We show that the ionization for different instant time intervals can be controlled by altering the time delay between the APT and the infrared pulse. Consequently, APT can be used as a tool to control the efficiency of high-order harmonics emitted at different times. By choosing appropriate APT and time delay, the driving pulse width for single attosecond pulse generation can be extended up to six optical cycles. (c) 2007 Optical Society of America.

Effects of Yb concentration on the spectroscopic properties of Yb : Y3Al5O12

Yb:YAG single crystals with Yb doping concentration 5.4, 16.3, 27.1, 53.6, and 100 at.% were grown by the Czochralski process. The effects of Yb concentration on the absorption spectra (190-1 100nm), fluorescence spectra under 940nm and X-ray excitation were studied. The concentration quenching of fluorescence was observed when the Yb doping concentration reaches to as high as 27.1 at.% for Yb:YAG. Under 940 nm excitation, the influence of the self-absorption at 969 and 1029 nrn on the fluorescence spectra is not evident when the Yb doping concentration is as high as 27.1 at.%. However, it can greatly change the shape of fluorescence spectra of Yb:YAG when the Yb doping concentration reaches to above 53.6 at.%. (c) 2005 Elsevier B.V. All rights reserved.

Upconversion luminescence in Yb3+-doped yttrium aluminum garnets

In this paper, we present results on upconversion luminescence performed on Yb3+-doped yttrium aluminum garnets under 940 nm excitation. The upconversion luminescence was ascribed to Yb3+ cooperative luminescence and the presence of rare earth impurity ions. The cooperative luminescence spectra as a function of Yb concentration were measured and the emission intensity variation with Yb concentration was discussed. Yb3+ energy migration quenched the cooperative luminescence of Yb:YAG crystals with doping level over 15 at%. (c) 2004 Elsevier B.V. All rights reserved.

Optical spectroscopy of Yb3Al5O12 single crystal

Yb3Al5O12 single crystal has been grown by Czochralski (CZ) method. The absorption spectrum was investigated at low temperature and the electronic energy levels for F-2(5/2) multiplet of Yb3+ in YbAG was proposed. The up-conversion emission of the crystal under 940 nm diode pumping and the X-ray excited luminescence (XEL) features of the crystal were also studied. (c) 2005 Elsevier B.V. All rights reserved.

Growth and spectroscopic characteristics of Yb : GSO single crystal

For the first time, a high optical quality 10 at.% Yb3+-doped gadolinium oxyorthosilicate laser crystal Gd2SiO5 (GSO) was grown by the Czochralski (Cz) method. The segregation coefficient of Yb3+ was studied by the inductively coupled plasma atomic emission spectrometer (ICP-AES) method. The crystal structure has monoclinic symmetry with space group P2(1)/c; this was determined by means of an x-ray diffraction analysis. The absorption spectra, fluorescence spectra and fluorescence decay curves of Yb3+ ions in a GSO crystal at room temperature were also studied. Then, the spectroscopic parameters of Yb:GSO were calculated. The advantages of the Yb:GSO crystal include high crystal quality, quasi-four-level laser operating scheme, high absorption cross-sections and particularly broad emission bandwidth (similar to 72 nm). The results indicated that the Yb:GSO crystal seemed to be a very promising laser gain medium in diode-pumped femtosecond laser and tunable solid state laser applications when LD pumped at 940 and 980 nm.

Yb：YAG晶体的合作发光现象

研究了Yb：YAG晶体的合作发光现象。当用940hm的近红外光激发时，Yb：YAG晶体有明显的上转换蓝色发光。实验发现498nm的蓝色发光强度与激发功率的平方成正比，而且Yb^3＋掺杂浓度越高，蓝色发光越强。分析表明这是Yb^3＋间强的相互作用导致的合作发光，是由于Yb^3＋在共价性的YAG基质中，它的4f^I3电子易于与近邻离子发生相互作用导致的。

LD抽运Yb:GSO实现1090nm低阈值激光运转

We report what we believe to be the first demonstration of laser operation with a novel laser material of Yb3(+) -doped Gd-2 SiO2 (Yb: GSO) pumped by a laser diode at 940 nm. We obtained a low lasing threshold of 1.27 kW/cm(2) with the center wavelength of 1090 nm, which is lower than the value of 1.53 kW/cm(2) predicted for Yb: YAG. The maximal output power of 360 mW was obtained with a 2% output, which corresponds to a slope efficiency up to 19%.

Characterization of diode-pumped laser operation of a novel Yb : GSO crystal

We report what is believed to be the first demonstration of the laser action of Yb3+ -doped Gd2SiO5 (Yb:GSO) crystal pumped by a 940-nm laser diode at room temperature. The threshold of laser generation is only 0.85 kW/cm(2), which is smaller than the theoretic threshold of Yb:YAG (1.54 kW/cm(2)). The laser wavelength is 1090 mn. With a 2.5% output coupler, the maximum output power is 415 mW under a pump power of 5 W. By using the SESAM, the Q-switched mode locking and CW mode-locked operations are demonstrated.