Inactivation and structural changes of E. Cloacae and B. Subtilis Endospores during IR laser water treatment

IR radiation has been studied for micro-organism inactivation of bacterial spores on metal substrates [1] and on metal and paper substrates [2]. A near-point near infrared laser water treatment apparatus for use in dental hand-pieces was also developed [3]. To date water sterilisation research using a mid-IR laser technique is very rare. According to the World Health Organisation [4], examinations for faecal indicator bacteria remain the most sensitive and specific way of assessing the hygienic quality of water. Bacteria that fall into this group are E. coli, other coliform bacteria (including E. cloacae) and to a lesser extent, faecal streptococci [5]. Protozoan cysts from organisms which cause giardiasis are the most frequently identified cause of waterborne diseases in developed countries [6,7]. The use of aerobic bacterial endospores to monitor the efficiency of various water treatments has been shown to provide a reliable and simple indicator of overall performance of water treatment[8,9].The efficacy of IR radiation for water disinfection compared to UV treatment has been further investigated in the present study. In addition FTIR spectroscopy in conjunction with Principle Component Analysis was used to characterise structural changes within the bacterial cells and endospores following IR laser treatment. Changes in carbohydrate content of E. cloacae following IR laser treatment were observed.

Dielectric Studies of laser ablated Ca doped BaTiO3 thin films

Recently, there has been growing interest in Ca modified BaTiO3 structures due to their larger electro-optic coefficients for their use in optical storage of information over conventional BaTiO3 crystals. Barium Calcium Titanate (BCT) shows promising applications in advanced laser systems, optical interconnects and optical storage devices. BaTiO3 thin films of varied Ca (3 at. % - 15 at. %) doping were deposited using pulsed laser ablation (KrF excimer laser) technique over Pt/Si substrates. The stoichiometric and the compositional analysis were carried out using EDAX and SIMS. The dielectric studies were done at the frequency regime of 40 Hz to 100 kHz at different ambient temperatures from 200 K to 600 K. The BCT thin films exhibited diffuse phase transition, which was of a typical non lead relaxor behavior and had high dielectric constant and low dielectric loss. The phase transition for the different compositions of BCT thin films was near the room temperature, showing a marked departure from the bulk phase transition. The C - V and the hysteresis behavior confirmed the ferroelectric nature below the phase transition and paraelectric at the room temperature.

Influência da aplicação de laser de baixa intensidade no recobrimento radicular associado à técnica de enxerto de tecido conjuntivo em indivíduos fumantes: ensaio clínico controlado randomizado

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of laser wavelength on Laser-Fired contacts for crystalline silicon solar cells

In the Laser-Fired Contact (LFC) process, a laser beam fires a metallic layer through a dielectric passivating layer into the silicon wafer to form an electrical contact with the silicon bulk [1]. This laser technique is an interesting alternative for the fabrication of both laboratory and industrial scale high efficiency passivated emitter and rear cell (PERC). One of the principal characteristics of this promising technique is the capability to reduce the recombination losses at the rear surface in crystalline silicon solar cells. Therefore, it is crucial to optimize LFC because this process is one of the most promising concepts to produce rear side point contacts at process speeds compatible with the final industrial application. In that sense, this work investigates the optimization of LFC processing to improve the back contact in silicon solar cells using fully commercial solid state lasers with pulse width in the ns range, thus studying the influence of the wavelength using the three first harmonics (corresponding to wavelengths of 1064 nm, 532 nm and 355 nm). Previous studies of our group focused their attention in other processing parameters as laser fluence, number of pulses, passivating material [2, 3] thickness of the rear metallic contact [4], etc. In addition, the present work completes the parametric optimization by assessing the influence of the laser wavelength on the contact property. In particular we report results on the morphology and electrical behaviour of samples specifically designed to assess the quality of the process. In order to study the influence of the laser wavelength on the contact feature we used as figure of merit the specific contact resistance. In all processes the best results have been obtained using green (532 nm) and UV (355 nm), with excellent values for this magnitude far below 1 mΩcm2.

室温下稳定的多波长掺铒光纤激光器的研究

通过在线形谐振腔中引入一段缠绕在压电陶瓷上的单模光纤作为正弦相位调制器，使得激射波长的损耗不固定，抑制由于掺铒光纤的均匀展宽效应引起的模式竞争，从而避免了在室温下不稳定的单波长激射，实现了多波长掺铒光纤激光器的稳定输出。为了获得平坦的多波长输出，在谐振腔里使用了一个损耗峰位于1530nm处的长周期光纤光栅，以获得较为平坦的增益谱。通过两个3dB耦合器制成的反射型梳状滤波器的滤波作用，实验中观察到稳定的多波长激射，相邻波长间隔约为0．45nm。中心9个波长的输出功率平坦度为10dB，边模抑制比大于25dB。

入射光偏振方向对LiNbO3晶体近光轴电光调制的影响

分析了在垂直LiNbO3晶体光轴方向加电压，光沿近光轴方向传播时，入射光偏振方向对电光调制器的影响。通过计算加电场后双折射光程差的变化和偏光振动方向的转动，画出在正交偏振镜下不同起偏方向的锥光干涉图，得到干涉图随起偏方向变化的规律：由偏光振动方向转动引起的消光区域随起偏方向的转动而转动，在起偏和检偏方向上始终消光，在与起偏方向成±45°角方向始终全透光，并且消光线的交点即感应双光轴头不随起偏方向的转动而变化，始终在折射率变大的感应主轴上。

平行平板角位移干涉测量仪的优化设计

提出一种可提高平行平板角位移干涉测量仪测量精度的优化设计方法。对角位移干涉测量系统进行了误差分析，讨论了影响角位移测量精度的主要因素。分析了在干涉仪光路中入射到平行平板上的初始入射角度、平行平板的折射率以及厚度等参数的选取对角位移测量精度的影响。结果表明，优化选取最佳的初始入射角度以及元件参数，并在干涉光路中附加引入一平面反射镜形成光程差放大系统，可实现的角位移测量精度达10-8 rad数量级。

一种基于平板横向剪切干涉的角位移测量方法

在一种已有的角位移干涉测量技术的基础上,提出一种改进的角位移测量方法。通过选择合适的初始入射角,使从平板前后表面反射的两光束实现剪切干涉。采用一维位置探测器测量光束经透镜会聚后在探测器光敏面上的光点偏移量。根据干涉信号的相位和光点偏移量可以计算出被测物体的角位移。在该测量方案中,引入的一平面反射镜与被测物体的反射面形成光程差放大系统,提高了角位移测量灵敏度。分析了初始入射角对剪切比的影响,并讨论了基于该方案的角位移测量精度。实验结果表明,基于该技术的角位移重复测量精度达到10-8 rad数量级。

偏振光飞秒双脉冲微加工

利用具有纳焦能量、高重复频率的偏振光飞秒双脉冲对金属铬膜样品进行微加工,样品表面都会产生微突起状结构,它们的宽度在0～400 ps的双脉冲时延范围内没有明显的变化,但高度却都在1～10 ps的双脉冲时延范围内呈现明显的下降,在此时延范围之外并没有明显的变化。通过加工样品的扫描电子显微镜(SEM)图片发现,对于偏振光,利用双脉冲方法,可以获得更好的加工质量。并且线偏振光得到的微突起状结构比较细长,在入射光束的偏振方向上有所伸长;圆偏振光得到的微突起状结构比较接近圆形。即在低脉冲能量、高重复频率情况下,具体的微加工特征形貌与入射光束的偏振状态有关。

调Q及连续掺Yb光纤激光器中的自锁模研究

在用半导体激光器抽运的单包层掺Yb调Q光纤激光器中观察到了清晰稳定的自锁模脉冲序列。脉冲包络形状为调Q脉冲。每个锁模脉冲的幅值由其在调Q脉冲中的相应位置决定。经过分析，认为自相位调制是调Q光纤激光器中产生锁模的主要原因。自相位调制的存在使得光脉冲的频谱被展宽，当这种展宽和腔的模式间隔相差不多时，腔内的模式便能相互作用，直到它们之间产生一个固定的相位关系。也即形成锁模。在此基础上。去掉声光晶体，并用两个光栅作为腔镜，实现了全光纤法布里-珀罗(F-P)腔锁模光纤激光器。改变腔结构，分别采用光栅和光纤反射圈作为

列阵透镜对能量测量影响的分析

结合列阵透镜的透过率分析了其后的光场分布。列阵透镜由多个列阵元拼接而成，用以改善主透镜焦点附近能量分布的均匀性。列阵透镜在提高辐照均匀性的同时，给能量测量带来了不利的影响。这是由于经过列阵元的相邻子光束会产生干涉，干涉条纹处的激光能量密度和功率密度相应都大为增加，其数值在干涉区域中心处能上升到原来的4倍。更高的能量密度和功率密度对能量计提出了更苛刻的要求。在没有采取适当措施的时候使用，就会损坏能量计。

基于光纤环形镜的全光脉冲整形器

提出了一种基于光纤环形镜的全光脉冲整形器。该全光脉冲整形器利用波分复用器将控制光脉冲引入光纤环形镜中，控制光脉冲由于交叉相位调制在信号光上产生了非线性附加相移。信号光在耦合器中发生干涉，经过整形的信号光脉冲从脉冲整形器的出射端出射，信号脉冲的波形由非线性附加相移的波形决定。实验中．利用对控制脉冲光谱整形和啁啾展宽的方法来对控制脉冲进行时间脉冲的整形，该全光脉冲整形器实现了对单纵模激光的脉冲整形，同时实现了飞秒脉冲和单纵模整形脉冲的精确同步。在理论上数值计算了该全光脉冲整形器的输出特性，理论计算结果和实验结

基于孔径耦合带状线的激光脉冲整形系统

实现了一种新型的激光脉冲整形系统，该系统使用了一个由孔径耦合带状线（ACSL）电脉冲整形器驱动的电光调制器。一个电脉冲整形器由两条通过其公共接地板上的耦合孔径发生耦合作用的带状传输线所组成的四端口装置。更换具有不同耦合孔径的公共接地板，该电脉冲整形发生器可以具有150ps时间结构的任意整形电脉冲。将任意整形的电脉冲输入到电光调制器上，就可以得到任意整形的激光脉冲。利用该系统，激光脉冲整形系统能够产生具有150ps前后沿，1～3ns脉冲宽度可调、高对比度、光滑过渡以及任意整形的激光脉冲。

高功率激光装置前端系统激光脉冲的时间整形及修正技术

针对激光惯性约束聚变实验研究对高功率激光驱动器前端系统复杂时间形状种子激光脉冲的需求, 应用孔径耦合带状线集成波导整形系统设计了满足需要的前端整形激光脉冲。用一种新方法精确计算了孔径耦合带状线电脉冲整形器的耦合系数和孔径宽度的数值关系, 并针对高衬比度整形激光脉冲的需求, 提出了高衬比度双极型集成波导整形系统方案。由该系统可以得到100 ps脉冲前沿、1～3 ns脉冲宽度可调、高衬比度(大于100∶1)、光滑无纹波调制、可精确满足神光II八路及第九路装置需求的前端整形激光脉冲。

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。