矢量圆对称Airy光束传输特性研究

以径向偏振圆对称Airy光束为例,基于Rayleigh-Sommerfeld矢量衍射理论,探讨了矢量圆对称Airy光束的传输特性。随着光束波长增大其自聚焦焦距减小,光束等效数值孔径增大。与傍轴理论计算结果比较后发现,当等效数值孔径大于0.09时,傍轴理论不再适用,因为此时傍轴理论低估了光波的衍射效应和矢量性。     

Effect of beam deflection oscillations on the weld geometry

The changes of seam profiles and of heat affected zones during electron beam welding at use of local beam deflection oscillations, directed across or along the joint, are studied. The possibility to control the beam cross-sectional profile on base of beam power, focus position and welding velocity is limited. In contrast to expectance an increased weld root radius and lack of spiking were found only when the position of the beam focus was significantly below the weld surface (about 18 mm), and when the oscillations were longitudinal to the work-piece movement. In all other studied regimes (at sharp focus on 13 mm bellow the work-piece surface, at focus positions situated less deeply or above the surface of the work-piece, at the oscillations along the joint, and at all beam focus positions for transverse beam oscillations) dagger-like shapes of the weld cross-sections were observed. The oscillations in the impinging electron beam had a small affect on the shape of the weld root, leading to the hypothesis of beam self-focusing in the bottom part of the keyhole, through which the beam reaches the root peaks. The regimes in which wider and more uniform cross-sectional weld shafts are connected to more soft thermal cycles of crystallisation in the weld pool (the joint become more acceptable), lead to lower weld depth (that is disadvantage). Statistical analyses of the experimentally observed weld geometric parameters are implemented and discussed. At linear longitudinal oscillations with frequency F_osc = 745 Hz, the weld depth not depend practically from the oscillation amplitudes at down focus positions, and maximal weld depths are observed at focusing currents in range 840–850 mA and at oscillation amplitudes 2–2.7 mm. At transverse sinusoidal oscillations the maximal weld depth is observed at higher oscillation amplitudes for focus positions bellow the sample surface and at small oscillation amplitudes at upper focus positions. There at oscillation amplitudes of order of 0.4–0.5 mm the sharp focus is coinciding with the sharp focus at not oscillating beam.     

高能量高效率钕玻璃再生放大器

为了获得高能量、高效率的钕玻璃前置放大器,设计了一套钕玻璃再生放大系统。通过调节单程增益和优化腔模设计,使得增益介质中的小尺度自聚焦效应得到有效控制。在重复频率1Hz运行下,获得最大输出能量21mJ、脉冲宽度2.65ns的激光输出,相应的光-光转换效率为5%,总增益达108,光束质量因子M2=1.5,脉冲能量稳定性均方根(RMS)值小于2%(超过2h连续工作),光谱的中心波长为1052.92nm。     

强激光非线性热像与克尔介质厚度的关系

通过理论分析与数值模拟方法,研究了高功率激光系统中非线性热像位置及光强随介质厚度的变化规律。基于角谱传输和Bespalov-Talanov小尺度自聚焦理论,在不作薄介质近似情况下得到了热像光强表达式,并用数值模拟结果进行了验证。结果表明,在一定的入射功率下,热像光强随介质厚度的增加而增大;而在一定的B积分下,热像光强随介质厚度的增加先单调增加,达到一极大值后,单调减小。此外,当模糊斑相对于克尔介质的距离的菲涅耳数远大于1时,可采用薄介质近似。数值模拟结果与解析结果吻合得很好。     

反射式光纤激光测距仪发射、接收光学系统的设计与研制

利用光学理论推导出反射式光纤激光测距仪的发射、接收光学系统的设计数据,提出并设计了发射和接收光学系统的机械结构,搭建了用于实验的反射式光纤激光测距仪的整体光学系统,探测到了10～100mW量级的回波光信号.     

相位共轭腔XeCl激光输出自聚焦的观察

采用布里渊镜构成ＸｅＣｌ激光腔，移动泵浦光束焦点使其置于布里渊液体介质底部液─固界面上某一合适的位置，可观察到输出的ＸｅＣｌ激光在远场有自聚焦现象。     

高频聚焦换能器的研制

介绍制作高频聚焦换能器的相关理论,设计各项工艺参数,介绍了主频为8～10 MHz的聚焦超声换能器的制作过程.论述了换能器性能测试过程,由测试结果及分析可知,换能器发射的脉冲宽度约4个周期,性能优良,能在检测中分辨1 mm平底孔当量的缺陷,基本达到了设计的预期效果.用研制的换能器进行柱塞孔检测,能明显检测到结合层的缺陷波.     

Nematicons and Their Electro-Optic Control: Light Localization and Signal Readdressing via Reorientation in Liquid Crystals

Liquid crystals in the nematic phase exhibit substantial reorientation when the molecules are driven by electric fields of any frequencies. Exploiting such a response at optical frequencies, self-focusing supports transverse localization of light and the propagation of self-confined beams and waveguides, namely “nematicons”. Nematicons can guide other light signals and interact with inhomogeneities and other beams. Moreover, they can be effectively deviated by using the electro-optic response of the medium, leading to several strategies for voltage-controlled reconfiguration of light-induced guided-wave circuits and signal readdressing. Hereby, we outline the main features of nematicons and review the outstanding progress achieved in the last twelve years on beam self-trapping and electro-optic readdressing.