Primary and secondary threshold intensities of ultraviolet-laser-induced domain nucleation in nearly stoichiometric LiTaO3

The primary and secondary threshold intensities of ultraviolet-laser-induced preferential domain nucleation in nearly stoichiometric LiTaO3 is observed. The primary threshold is the minimum intensity to achieve the instantaneous preferential domain nucleation within the focus by the combined action of irradiation and electric fields. The secondary threshold is the minimum intensity to achieve the memory effect without any irradiation within the original focus. The space charge field created by the photoionization carriers is thought to be responsible for the instantaneous effect. The explanation based on the formation and transformation of extrinsic defect is presented for the memory effect. (c) 2008 American Institute of Physics.

Three-port beam splitter of a binary fused-silica grating

A deep-etched polarization-independent binary fused-silica phase grating as a three-port beam splitter is designed and manufactured. The grating profile is optimized by use of the rigorous coupled-wave analysis around the 785 nm wavelength. The physical explanation of the grating is illustrated by the modal method. Simple analytical expressions of the diffraction efficiencies and modal guidelines for the three-port beam splitter grating design are given. Holographic recording technology and inductively coupled plasma etching are used to manufacture the fused-silica grating. Experimental results are in good agreement with the theoretical values. (c) 2008 Optical Society of America.

Effects of the frequency chirp on the fields of a chirped Gaussian pulse passing through a hard-edged aperture

Based on the Huygens-Fresnel diffraction integral and Fourier transform, propagation expression of a chirped Gaussian pulse passing through a hard-edged aperture is derived. Intensity distributions of the pulse with different frequency chirp in the near-field and far-field are analyzed in detail by numerical calculations. In the near-field, amplitudes of the intensity peaks generated by the modulation of the hard-edged aperture decrease with increasing the frequency chirp, which results in the improving of the beam uniformity. A physical explanation for the smoothing effect brought by increasing the frequency chirp is given. The smoothing effect is achieved not only in the pulse with Gaussian transverse profile but also in the pulse with Hermite-Gaussian transverse profile when the frequency chirp increases. (C) 2005 Elsevier B.V. All rights reserved.

Transverse intensity distributions of a broadband laser modulated by a hard-edged aperture

By means of the Huygens-Fresnel diffraction integral, the field representation of a laser beam modulated by a hard-edged aperture is derived. The near-field and far-field transverse intensity distributions of the beams with different bandwidths are analyzed by using the representation. The numerical calculation results indicate that the amplitudes and numbers of the intensity spikes decrease with increasing bandwidth, and beam smoothing is achieved when the bandwidth takes a certain value in the near field. In the far field, the radius of the transverse intensity distribution decreases as the bandwidth increases, and the physical explanation of this fact is also given. (c) 2005 Optical Society of America.

增益随机散射介质中的非相干辐射

用蒙特卡罗方法仿真了增益随机散射体中的非相干辐射，观察了非相干随机激光的特性。当抽运能量超过一定阈值时，散射体的整体辐射谱突然变窄；随着抽运能量继续增大，在光滑谱背景上会出现分离尖峰；散射体内空间某位置处频率组成不是单一的；辐射谱中某单个频率的空间方向分布和位置分布比较广。增益随机散射体中产生的非相干随机激光本质上既不同于无反馈的普通放大自发辐射，又不同于相干反馈形成的常规激光。解释了非相干随机激光辐射谱上出现分离尖峰的原因，出现这种现象是由于少数光子在增益散射体中经历较多次数散射后得到了相对充分的放大。

Stable pulse-compressed acousto-optic Q-switched fiber laser

A novel acousto-optic switch operation by a simple laser-diode pumped acousto-optic, Q-switched, ytterbium-doped, double-clad fiber laser is reported. Stable compressed Q-switched sub-40 ns pulses with a beam quality factor (M-2 = 2) are achieved at the repetition rate of 1-50 kHz. Q-switched pulses of similar to 20 mu J pulse energy and 35 as pulse width are obtained at the repetition rate of 50 kHz. Finally, a reasonable explanation of the novel Q-switched operation is presented. (c) 2007 Optical Society of America.

Dual-wavelength competitive output in Nd:Y3Sc1.5Al3.5O12 ceramic disk laser

In this paper, we demonstrated a dual-wavelength competitive output in Nd:Y3SC1.5Al3.5O12 ceramic disk laser. Different dual-wavelength output behaviors for Nd:YSAG and Nd:YAG ceramic disk laser were investigated and discussed. By applying the energy transfer model, we suggested the reasonable explanation for this new phenomenon as the disordered replacing of Al3+ ions by Sc3+ ions. The main advantage of the dual-wavelength ceramic laser is the possibility to serve as the seed source to generate Terahertz radiation. (C) 2008 Elsevier B.V. All rights reserved.

Laser-induced damage of Ta2O5/S1O2 narrow-band interference filters under different 1064 nm Nd : YAG laser modes

The laser-induced damage (LID) behavior of narrow-band interference filters was investigated with a Nd:YAG laser at 1064 nm under single-pulse mode and free-running mode. The absorption measurement of such coatings was performed with surface thermal lensing (STL) technique. The damage morphologies under the two different laser modes were also studied in detail. It was found that all the filters exhibited a pass-band-center-dependent absorption and laser-induced damage threshold (LIDT) behavior, but the damage morphologies were diverse. The explanation was given with the analysis of the electric field distribution and the operational behavior of the irradiation laser. (c) 2005 Elsevier B.V. All rights reserved.

中国毛乌素沙地土壤-植物-大气系统中植物水分关系的定性及定量解释

本研究通过探讨毛乌素沙地主要犀生植物和中生植物的冰分关系。对“翠生植物”的概念作了进一步的分析和阐述，探讨了燕腾作用、光合作用的气孔调节与植物叶片水分平衡的相互关系，并提出了以蒸腾“午休一为基础的关于捌分植物水分生态类型的新概念。上述问题的探讨可作为对中圈毛乌素沙化草地植物环境系统优化模式的水平衡假说的验证。 探讨了为合理确定在研究地区种蕈造林的最佳密度所需进一步研究的内容：水分亏缺对植物量累积的抑制作用。并对该地区主要植物种的季节蒸腾耗水量作了估算。 研究了依赖于主导环境因子的沙生植物蒸腾速率的回归模型。得出结论认为：对手蒸腾速率和叶面积指数，建立多元非线性回归可以取得较好结果。 最后，对几个重要的蒸散预测模型和土壤水分运动的物理模型进行了评述，并探讨了这些模型对于干旱区蒸散预测研究的可行性，作为本研究的未来探讨的课题。