飞秒激光在银膜表面诱导亚波长周期条纹的超快成像研究

采用440 nm空间分辨、亚皮秒时间分辨的泵浦探测成像技术,本文研究了800 nm飞秒激光脉冲照射银膜表面后亚波长周期条纹的形成动力学.分析了1~6个飞秒脉冲照射下银膜表面条纹结构的演化过程.第一个激光脉冲在薄膜表面诱导凹槽等缺陷结构;第二个激光脉冲以后表面开始出现亚波长周期条纹,并且在更多脉冲照射时进行纵向和横向生长.条纹在50~70 ps以后开始出现,随延迟时间增加不断加深变长,在演化过程中条纹位置保持不变;形成过程在1 000 ps内基本结束.研究结果表明,飞秒激光在薄膜表面诱导凹槽等缺陷结构在后面的激光脉冲照射表面过程中激发了表面等离激元,进而导致的周期性能量沉积在亚波长周期条纹形成过程中起了关键作用,材料表面的熔化导致了之前形成的条纹变浅以及部分消失.     

飞秒激光与硅样品作用生成纳米光栅结构

我们用脉冲宽度120 fs、波长800nm、能量密度从0.1 J/cm2~0.5 J/cm2的激光束照射硅样品和锗硅合金样品表面能够生成各种低维形貌结构。特别是将飞秒激光束散焦至直径为100μm的束斑,并以每秒1000个脉冲照射硅样品表面两秒钟时(能量密度在熔融阈值0.2 J/cm2附近),能生成周期间隔为400nm的浮雕光栅状的一维微结构。我们用飞秒激光与其诱导的等离子体波的相干模型解释了光栅状微结构的形成机理。还发现这种结构有很强的PL发光,PL峰的中心约在719nm处。该飞秒激光加工技术既简捷又稳定,在光学和微电子加工领域应有很好的应用前景。     

飞秒激光诱导Al_2O_3陶瓷表面微纳结构及润湿特性研究

飞秒激光以其极短脉宽和极高的峰值功率几乎可以胜任任何材料的加工.利用飞秒激光微加工平台,通过单点烧蚀和线扫描微加工的方式,在工业级氧化铝陶瓷材料表面诱导出随机分布的纳米结构和条纹结构,条纹结构的周期约为314 nm.文章研究了激光脉冲个数、扫描速度和偏振方向等参数对氧化铝陶瓷表面微纳结构形成的影响.结合激光直写技术,在陶瓷表面诱导出大面积的微纳结构分布,分析了加工前后陶瓷表面润湿特性的变化,实现了陶瓷表面改性.     

飞秒激光诱导氧化锌晶体表面纳米条纹的相干连接

介绍了飞秒激光脉冲辐照氧化锌晶体表面诱导纳米条纹的相干连接,通过调整两次激光扫描区域的间距,两次独立形成的纳米条纹可以相干的连接起来,形成更长的纳米光栅.这样就解决了以前诱导光栅尺寸由激光聚集光斑大小限制的问题.Raman线扫描技术表征了相干连接的质量,并对相关的物理机制做了讨论.这种技术可以利用飞秒激光制作大尺寸的自组装纳米光栅.     

超快激光散斑场的时空相干特性

将超快激光应用到对散斑现象的研究领域.首先从散斑统计理论和光的相干性角度出发,给出入射飞秒脉冲的自相关函数分布及光强经过粗糙随机表面后的光强演化形式.从实验上通过用飞秒激光脉冲光源照射粗糙的随机表面衍射屏,得到了一系列明显区别于传统普通的连续光形成的散斑场.在超快散斑场中出现了纤维辐射状的结构,散斑图样整体呈由中心光斑状向四周辐射形成条纹状光斑的分布.     

ZnS∶Cu纳米微粒的线性光学特性研究

采用溶胶-凝胶法在不同条件下制备了ZnS∶Cu纳米微粒,合成中首次用中性硫代乙酰胺分子对纳米微粒表面进行修饰.所制ZnS∶Cu纳米微粒在紫光灯的照射下,呈现绿色发光现象;在 332 nm的紫外光激发下,ZnS∶Cu纳米微粒产生位于516 nm的发射峰;相对于体相材料在462 nm的发射峰红移了54 nm;另外,样品的紫外吸收光谱表明,位于290 nm的吸收峰,相对于体相材料蓝移了50.6 nm.     

ZnS：Cu纳米微粒的线性光学特性研究

采用溶胶-凝胶法在不同条件下制备了ZnS∶Cu纳米微粒,合成中首次用中性硫代乙酰胺分子对纳米微粒表面进行修饰。所制ZnS∶Cu纳米微粒在紫光灯的照射下,呈现绿色发光现象;在332 nm的紫外光激发下,ZnS∶Cu纳米微粒产生位于516 nm的发射峰;相对于体相材料在462nm的发射峰红移了54 nm;另外,样品的紫外吸收光谱表明,位于290 nm的吸收峰,相对于体相材料蓝移了50.6 nm.     

飞秒激光直写加工及结构信息快速存储

用飞秒激光直写方法辅以平台操作程序将设计好的二维和三维微结构图形信息成功地记录在石英玻璃内部.其优点是微结构样式可以由实验者自由灵活设计,采用飞秒激光可以对多种材料进行加工.该技术可以将商标、标识码等写入各种商品和证件内部进行防伪识别,还可以在贵重金属首饰表面写入照片进行个性化制作.     

飞秒激光在蓝宝石晶体表面加工微细结构的实验研究

由于蓝宝石晶体具有很高的硬度和耐磨蚀性,很难进行机械和化学腐蚀加工。笔者利用波长780 nm、频率1 kHz和脉冲宽度164 fs的飞秒脉冲激光在蓝宝石晶体表面进行了微细结构加工的实验研究。采用飞秒激光静态照射蓝宝石晶体表面,通过飞秒激光烧蚀孔的直径和脉冲能量的关系,计算了飞秒激光烧蚀蓝宝石晶体的两种烧蚀状态下的烧蚀阈值和有效烧蚀半径。通过直线扫描实验,在不同实验条件下在蓝宝石晶体表面加工微槽,获得微槽的宽度和深度与飞秒激光主要参数之间的关系。研究结果表明,微槽的加工表面可通过增加扫描次数而得到明显的提高,且扫描次数的增加对微槽的宽度和深度基本无影响。利用聚焦的飞秒激光束沿着轨迹扫描,在蓝宝石晶体表面加工出比较清洁的微小结构,可以为实现微结构的精密加工提供指导。     

飞秒激光偏振角及入射角对金属表面周期结构的影响

飞秒激光对金属Cu、Ag材料表面的烧蚀作用源于飞秒激光超高强的脉冲功率密度,基于表面散射波模型的理论,在实验上探究P偏振飞秒激光偏振角和入射角对金属表面周期性微纳光栅结构的影响.首次通过偏振角及入射角的双重改变,得到入射角阈值规律,并且得到斜入射时光栅周期随入射角增大的事实.     

飞秒脉冲在透明介质中的三维光存储及读出对比度研究

将波长为800nm，脉冲宽度为150fs的近红外激光脉冲，聚焦到聚甲基丙烯酸甲酯(Ploymethyl Metacrtlate，简记PMMA)和熔融石英中，实现了三维逐位式光数据存储．分别记录了5，10，15和20层数据位点，并利用相位对比光学显微原理，对各层数据并行读出，从而分析了各层数据位点读出对比度的变化．结果表明，各层数据位点的折射率对比度由内至外依次增加．记录层数越多，内部层的对比度下降越明显．由于飞秒激光脉冲与透明介质相互作用中熔融石英比PMMA内部产生的残余应力大，因此，在数据位点参数相同的情况下，利用聚甲基丙烯甲酯(PMMA)材料记录的层数更多．     

Adaptive subwavelength control of nano-optical fields

Adaptive shaping of the phase and amplitude of femtosecond laser pulses has been developed into an efficient tool for the directed manipulation of interference phenomena, thus providing coherent control over various quantum-mechanical systems. Temporal resolution in the femtosecond or even attosecond range has been demonstrated, but spatial resolution is limited by diffraction to approximately half the wavelength of the light field (that is, several hundred nanometres). Theory has indicated that the spatial limitation to coherent control can be overcome with the illumination of nanostructures: the spatial near-field distribution was shown to depend on the linear chirp of an irradiating laser pulse. An extension of this idea to adaptive control, combining multiparameter pulse shaping with a learning algorithm, demonstrated the generation of user-specified optical near-field distributions in an optimal and flexible fashion. Shaping of the polarization of the laser pulse provides a particularly efficient and versatile nano-optical manipulation method. Here we demonstrate the feasibility of this concept experimentally, by tailoring the optical near field in the vicinity of silver nanostructures through adaptive polarization shaping of femtosecond laser pulses and then probing the lateral field distribution by two-photon photoemission electron microscopy. In this combination of adaptive control and nano-optics, we achieve subwavelength dynamic localization of electromagnetic intensity on the nanometre scale and thus overcome the spatial restrictions of conventional optics. This experimental realization of theoretical suggestions opens a number of perspectives in coherent control, nano-optics, nonlinear spectroscopy, and other research fields in which optical investigations are carried out with spatial or temporal resolution.     

Optical nonlinearity and ultrafast dynamics of ion exchanged silver nanoparticles embedded in soda-lime silicate glass

Ag nanoparticles embedded in soda-lime silicate glass were fabricated by ion-exchange and subse-quently annealing method. Z-scan technique, femtosecond time-resolved optical Kerr effect （OKE） technique and femtosecond pump-probe experiment were used to investigate the effects of laser wavelength and laser pulse duration as well as annealing temperature on the third-order optical nonlinearity and ultrafast dynamics of the composites. It was found that the third-order susceptibility of Ag nanoparticles composite glass measured by 400 nm pulse source is larger than that measured by 800 nm pulse source due to an enhancement effect of local field near surface plasmon resonance of Ag nanoparticles in silicate glass. The third-order optical nonlinearity measured by ns laser source is about two orders of magnitude larger than that measured from fs pulse. The annealing temperature has an important effect on the third-order optical nonlinearity and ultrafast dynamics of the composites. Third-order nonlinear susceptibility up to 10^-l0 esu and fast relaxation process up to 0.2 ps have been obtained in Ag nanoparticles doped glass.     

ZnS/PVA纳米复合薄膜的制备及其非线性三光子吸收研究

采用原位复合的方法制备出厚度为20μm的聚乙烯醇(PVA)与ZnS纳米微粒复合的薄膜,利用透射电镜(TEM)和X射线衍射(XRD)研究薄膜样品的微结构性能,证明已制备出立方晶相的针状ZnS纳米晶.用Z-扫描技术研究ZnS/PVA纳米复合薄膜的非线性光学性质,发现该薄膜对532 nm纳秒脉冲激光表现出较强的非线性吸收效应,而且非线性吸收强度随入射光强的增加而减少.该非线性吸收主要由纳米ZnS的三光子吸收引起,并伴随弱饱和吸收现象发生.     

磁控溅射ZnO薄膜的三阶非线性光学特性

采用磁控溅射技术在SiO_2衬底上制备ZnO薄膜,并通过X射线衍射仪、原子力显微镜、紫外-可见分光光度计和荧光光谱仪对薄膜的晶体结构、表面形貌、带隙宽度和光致发光性质进行测试表征,结合飞秒激光(波长为800nm,脉宽50fs)和Z扫描方法测量该薄膜的三阶非线性光学特性.结果表明,其三阶非线性折射率和非线性吸收系数均为正值,分别为3.50×10-18 m2/W和2.88×10-11 m/W.     

Control of the carrier-envelope phases of a synchronously pumped femtosecond optical parametric oscillator and its applications

The intrinsic synchronization, multi-color outputs and related carrier-envelope phases （CEP） among pulses bring advantages to synchronously pumped femtosecond optical parametric oscillators and the pumping sources for broadband frequency comb generation and ultrashort waveform coherent syn-thesis. In this paper, we discuss our latest research results in this field, which cover the following as-pects： the phase relationship and energy conservation law in an OPO and related experimental verifi-cation; control of the pumping Ti-sapphire femtosecond laser＇s CEP by self-referencing technology, and its repetition-rate locking by piezoelectric transducer （PZT）; CEP locking of the pulses from the OPO by beating the non-phase-matched visible outputs against pump supercontinuum to obtain a driving signal for a fast PZT on the OPO end mirror; the generation of a broadband frequency comb spanning from 400 nm to 2.4 μm with 1.2 kHz bandwidth; and the realization of coherent interference between phase controlled pump pulses and signal second harmonic pulses.     

Preparation of porous microstructures on NiTi alloy surface with femtosecond laser pulses

Porous microstructures on Nickel-Titanium （NiTi） alloy surfaces were prepared by linearly polarized femtosecond lasers with moving focal point at a certain speed. It was found that various novel micro- structures from feather-like ripples to cluster-like porous textures could be formed with increasing laser energy. Particularly, when the laser energy was 400 llJ, a periodic porous metal surface was gen- erated. Measurement of X-ray diffraction showed that the grains on the sample surface were refined through femtosecond laser ablation processes, but the crystal structures still kept their original states. Analysis by X-ray photoelectron spectroscopy revealed that Ni/l＂i on the sample surface was changed with an evident oxidization of titanium element under different laser energies. This investigation pro- vides a new approach to improve the biocompatibility of NiTi-based implant devices.     

测量飞秒光参量产生器输出光脉冲脉宽的自相关仪的设计

设计出一台只用一块非线性晶体就能够测量宽波长范围的飞秒激光脉冲脉宽的单次脉冲自相关仪,适用于测量由光参量产生获得的可调谐飞秒激光脉冲的脉宽.     

Probing carrier dynamics in nanostructures by picosecond cathodoluminescence

Picosecond and femtosecond spectroscopy allow the detailed study of carrier dynamics in nanostructured materials. In such experiments, a laser pulse normally excites several nanostructures at once. However, spectroscopic information may also be acquired using pulses from an electron beam in a modern electron microscope, exploiting a phenomenon called cathodoluminescence. This approach offers several advantages. The multimode imaging capabilities of the electron microscope enable the correlation of optical properties (via cathodoluminescence) with surface morphology (secondary electron mode) at the nanometre scale. The broad energy range of the electrons can excite wide-bandgap materials, such as diamond- or gallium-nitride-based structures that are not easily excited by conventional optical means. But perhaps most intriguingly, the small beam can probe a single selected nanostructure. Here we apply an original time-resolved cathodoluminescence set-up to describe carrier dynamics within single gallium-arsenide-based pyramidal nanostructures with a time resolution of 10 picoseconds and a spatial resolution of 50 nanometres. The behaviour of such charge carriers could be useful for evaluating elementary components in quantum computers, optical quantum gates or single photon sources for quantum cryptography.     

光阱中多个金纳米棒的双光子荧光效应及热熔合过程

本文利用单束、波长对应金纳米棒长轴表面等离子共振的飞秒脉冲激光对多个长度为40 nm,直径为10 nm的金纳米棒颗粒进行了光捕获,系统研究了金纳米棒颗粒在共振激光作用下的双光子荧光及光致热熔合效应.实验结果表明,在光阱捕获过程中金纳米棒颗粒会激发出明显的双光子荧光.当多个金纳米棒被光力捕获在光斑中心时,金纳米棒发生热熔化并熔合成大尺寸的金纳米团簇.利用这种单光束光镊熔合技术,我们在玻璃衬底上制备了二维有序的金纳米团簇阵列.这一研究对利用金纳米棒颗粒来制备微纳光子结构及多功能光子器件等具有重要的指导意义.