Fabrication of two-dimensional periodic nanostructures by two-beam interference of femtosecond pulses

Two-dimensional periodic nanostructures on ZnO crystal surface were fabricated by two-beam interference of 790 nm femtosecond laser. The long period is, as usually reported, determined by the interference pattern of two laser beams. Surprisingly, there is another short periodic nanostructures with periods of 220-270 nm embedding in the long periodic structures. We studied the periods, orientation, and the evolution of the short periodic nanostructures, and found them analogous to the self-organized nanostructures induced by single fs laser beam. (C) 2008 Optical Society of America.

飞秒激光微加工：激光精密加工领域的新前沿

飞秒激光微加工技术具有加工精度高、热效应小、损伤阈值低以及能够实现真正的三维微结构加工等优点,这些特性是传统的激光加工技术所无法取代的。首先回顾了激光微加工和超短脉冲激光技术的发展历史,然后介绍超短脉冲激光与金属和介质材料相互作用的机制,接着阐述了飞秒激光直写、干涉和投影制备等各种加工方法的原理,重点讨论飞秒激光在三维光子器件集成、微流体芯片制备及其在生化传感方面的应用等,最后展望了飞秒激光微加工领域所面临的机遇和挑战,指出了未来的研究方向。

超短脉冲激光对透明材料的破坏

基于固体的能带理论和能量守恒原理建立了一个描述激光与非金属材料作用时载流子随时间空间变化的理论模型。讨论了材料的破坏阈值、烧蚀深度与激光脉宽、波长和强度之间的关系，同时也讨论了破坏阈值、烧蚀深度与材料禁带宽度等特性之间的关系。讨论了多光子电离、隧道电离和雪崩电离在激光对材料破坏过程中的不同地位，理论结果表明，光电离在超短脉冲激光对非金属材料破坏过程中对破坏阈值的影响最大。

Phase-sensitive atom localization in a loop Lambda-system

The behaviour of the Lambda-system has been studied theoretically in the context of atom localization. In addition to the probe field and the standing wave driving field, a microwave field is introduced to couple the two lower states, and as a result our Lambda-system forms a closed loop. Therefore phase-sensitive atom localization is expected. Indeed by appropriate choice of the relative phase between three fields, an improvement by a factor of 2 has been found in the detection probability of atoms within the sub-wavelength domain of the standing wave. The effect of other parameters is also investigated.

Near-field hexagonal array illumination based on fractional Talbot effect

Hexagonal array is a basic structure widely exists in nature and adopted by optoclectronic device. A phase plate based on the fractional Talbot effect that converts a single expanded laser beam into a regular hexagonal array of uniformly illuminated apertures with virtually 100% efficiency is presented. The uniform hexagonal array illumination with a fill factor of 1/12 is demonstrated by the computer simulation. (C) 2006 Elsevier GmbH. All rights reserved.

Designing a coupler for the intersatellite optical communication system

Coupling a single-mode laser diode with 200 mW to a single-mode fiber (SMF) through an orthonormal aspherical cylindrical lens and a GRIN lens for the intersatellite optical communication system is proposed and demonstrated. We experimentally studied how the coupling efficiency changes with the SMF's position displacement and axial angle variation, and obtained 80 mW output power at the end of the SMF, which shows that the coupling units have satisfied the designed request. (c) 2007 Elsevier GmbH. All rights reserved.

Structure and properties of amorphous thin film for optical data storage

In this paper the magnetic and magneto-optical properties of amorphous rare earth-transition metal (RE-TM) alloys as well as the magnetic coupling in the multi-layer thin films for high density optical data storage are presented. Using magnetic effect in scanning tunneling microscopy the clusters structure of amorphous RE-TM thin films has been observed and the perpendicular magnetic anisotropy in amorphous RE-TM thin films has been interpreted. Experimental results of quick phase transformation under short pulse laser irradiation of amorphous semiconductor and metallic alloy thin films for phase change optical recording are reported. A step-by-step phase transformation process through metastable states has been observed. The waveform of crystallization propagation in micro-size spot during laser recording in amorphous semiconductor thin films is characterized and quick recording and erasing mechanism for optical data storage with high performance are discussed. The nonlinear optical effects in amorphous alloy thin films have been studied. By photo-thermal effect or third order optical nonlinearity, the optical self-focusing is observed in amorphous mask thin films. The application of amorphous thin films with super-resolution near field structure for high-density optical data storage is performed. (c) 2007 Elsevier B.V. All rights reserved.

激光稳频的共焦法布里-珀罗干涉仪

针对多普勒激光雷达激光源短期频率漂移低于1 MHz的要求,设计了一种共焦干涉仪作为频率标准进行稳频。通过对三种不同材料制成的共焦法布里-珀罗(Fabry-Perot)干涉仪中心频率随温度漂移情况进行分析对比,选用零膨胀微晶玻璃材料制作共焦法布里-珀罗干涉仪,腔镜和隔离器通过光胶的方式进行组合,并且置于温控精度优于0.01 K的双层密封温控箱中。经过实验测量,共焦法布里-珀罗干涉仪的自由光谱范围为370 MHz,透射谱半峰全宽(FWHM)为1.7 MHz,精细度为220。采用该共焦干涉仪进行稳频,理论稳频精度可达0.15 MHz,满足激光多普勒雷达单频激光源的稳频要求。

多普勒激光雷达及其单纵模全固态激光器

设计一套测量大气风场的多普勒激光雷达系统,以种子注入的单频、高重频、脉冲紫外全固态激光器为发射光源,采用两种直接探测技术获取高低空大气风场。基于费索干涉仪（Fizeau）的条纹图像技术获取边界层和低对流层大气风场,基于双法布里珀罗干涉仪（DFP）的双边缘检测技术获取高对流层和低平流层风场。研制的单频全固态激光器输出100 Hz、30 mJ的单纵模脉冲激光,输出线宽达到傅里叶转换极限。报道了测量原理和数值模拟结果、实验样机和系统技术参数。系统将用于移动式高低空大气风场测量。

7.3 W国产单频光纤放大器

报道了一种MOPA式国产单频光纤放大器。该放大器采用连续波单频激光器作为主振荡器，采用我国自行设计和制造的大模场面积掺Yb双包层光纤作为功率放大器，在波长1064 nm处实现了最高7.3 W的连续激光输出，斜率效率为39%，光－光转换效率为26%。此外，对光谱特性及放大的自发发射的抑制也进行了探讨。

注入锁定激光器的边带锁频技术稳频系统优化分析

介绍了边带锁频技术稳频方法，推导出鉴频曲线，对稳频控制过程进行了分析．建立了注入锁定激光器的边带锁频技术稳频系统理论模型，讨论了相关参量对稳频效果的影响并且进行了优化．结果表明，增加入射光强，采用窄线宽的法布里一珀罗以及对法布里一珀罗进行高准确度温控都可以增强稳频效果．提出适用于注入锁定激光器的两种稳频方案并进行比较．

Fabrication and spectral properties of Nd3+-doped yttrium lanthanum oxide transparent ceramics

Transparent 1 at% Nd3+:Y1.9La0.1O3 ceramics were fabricated with nanopowders prepared by carbonate coprecipitation method. The powder compacts were sintered in H-2 atmosphere at 1550 degrees C for 30 h. The Nd3+:Y1.9La0.1O3 ceramics display uniform grains of about 50 mu m and high transparency. The highest transmittance of the ceramics reaches 67%. The strongest absorption peak is in the wavelength of 820 nm with absorption cross section of 2.48 x 10(-20) cm(2). The absorption is still high at LD wavelength 806 nm with absorption cross section of 1.78 x 10(-20) cm(2) and broad full width at half maximum (FWHM) of about 6.3 nm. The strongest emission peak was centered at 1078 nm with large stimulated emission cross section of 9.63 x 10(-20) cm(2) and broad FWHM of about 7.8 nm. The broad absorption and emission bandwidth of Nd3+:y(1.9)La(0.1)O(3) transparent ceramics are favorable to achieve the miniaturized LD pumping apparatus and ultrashort modelocked pulse laser output, respectively. (c) 2007 Elsevier B.V. All rights reserved.

飞秒脉冲激光器中色散补偿膜的设计

阐述了用光学薄膜进行色散补偿的基本原理，介绍了设计的基本过程．根据Ti：Sapphire飞秒激光器中腔内色散补偿的要求，设定了色散补偿目标，通过计算机优化，得到了一种40层的Ta2O5／SiO2介质膜系．该膜系能在720～870am范围获得大于99．5％的反射率，在510～550nm获得大于90％的透射率，在740～850nm提供较平滑的-40fs^2的群延迟色散．这样的结果经过7次反射后，可以补偿5-mm Ti：sapphire晶体产生的绝大部分群延迟色散。

短脉冲激光辐照下熔融石英薄膜的损伤机理

激光诱导薄膜损伤过程中，雪崩离化（AI）和多光子离化（MPI）的性质和作用到目前仍然存在争议。基于STUART等人的电子密度演化方程，运用数值模拟方法，研究了脉宽为τ∈[0．01，5]ps范围内单脉冲激光作用下熔融石英薄膜中电子密度演化过程；讨论了初始电子密度、激光脉冲宽度对阈值功率密度和阈值能量的影响；分析了初始电子密度、激光脉冲宽度对多光子离化及雪崩离化的影响。研究结果表明，在所研究的脉宽范围内，对于熔融石英光学薄膜、飞秒激光诱导损伤以雪崩离化为主导，多光子离化的影响随着脉宽的降低而增强，雪崩离化所需种子电子主要来源于多光子离化。

用于钕玻璃啁啾脉冲放大系统光谱整形的多层介质膜反射镜

在千焦拍瓦高功率啁啾脉冲放大系统设计中,为了尽量消除增益窄化和增益饱和效应的影响,同时尽可能提高高功率激光输出脉冲信噪比参数,激光脉冲时空和光谱的整形问题备受关注.提出一种光谱整形新方法,利用特定结构的多层介质膜反射镜,可实现对大能量高功率啁啾脉冲钕玻璃放大系统中啁啾脉冲的光谱整形.研究结果表明,只要合理选择多层介质膜系的结构参数,可有效地控制其反射率分布,且在保证反射相位基本不变的条件下其调制度可超过60%.针对钕玻璃1053nm波长设计而成的光谱整形反射镜,反射带宽可达到196nm,色分辨率约为0.1nm,在几十纳米波长范围所对应的相位偏差小于12mrad,相当于λ/524,能够满足"神光Ⅱ"千焦拍瓦改造的技术指标要求.