飞秒激光诱导玻璃内Ba2TiSi2O8晶体的析出

使用聚焦后的800nm,150fs,250kHz的高重复频率飞秒脉冲激光器能够在BaO-TiO₂-SiO₂组分的玻璃内部三维选择性地诱导Ba₂TiSi₂O₈晶体的析出. 发光光谱显示这种晶体把入射的800nm光转化成了400nm的蓝光,因此这种析出的晶体具有非线性倍频特性. 通过拉曼光谱测定,在当前的玻璃组分中析出的晶体是Ba₂TiSi₂O₈. 研究表明,经250kHz的飞秒激光辐照一段时间后,在玻璃内部由于脉冲能量的连续沉积会使得激光辐照区域出现热积累效应,因此,该辐照区域的温度会不断升高以致超过玻璃析晶温度,最终诱导玻璃熔融析晶. 此外,对飞秒激光辐照区域不同部位进行拉曼光谱检测,结果表明：在整个区域Ba₂TiSi₂O₈晶体的析出呈现中间比外围明显的分布特点,因此晶体析出与辐照形成的温度梯度场有密切关系.     

飞秒激光诱导玻璃内Ba2TiSi2O8晶体的析出

使用聚焦后的800nm,150fs,250kHz的高重复频率飞秒脉冲激光器能够在BaO-TiO₂-SiO₂组分的玻璃内部三维选择性地诱导Ba₂TiSi₂O₈晶体的析出. 发光光谱显示这种晶体把入射的800nm光转化成了400nm的蓝光,因此这种析出的晶体具有非线性倍频特性. 通过拉曼光谱测定,在当前的玻璃组分中析出的晶体是Ba₂TiSi₂O₈. 研究表明,经250kHz的飞秒激光辐照一段时间后,在玻璃内部由于脉冲能量的连续沉积会使得激光辐照区域出现热积累效应,因此,该辐照区域的温度会不断升高以致超过玻璃析晶温度,最终诱导玻璃熔融析晶. 此外,对飞秒激光辐照区域不同部位进行拉曼光谱检测,结果表明：在整个区域Ba₂TiSi₂O₈晶体的析出呈现中间比外围明显的分布特点,因此晶体析出与辐照形成的温度梯度场有密切关系.     

飞秒激光空间选择性诱导玻璃微结构及应用

利用飞秒激光与玻璃的非线性相互作用，可以对玻璃进行空间选择性微观改性与修饰，赋予新的光功能．本文介绍飞秒激光的持点及其对玻璃微结构的改性，以及近年来利用飞秒激光进行玻璃的缺陷控制、光活性离子(稀土、过渡和重金属离子)价态操作、微晶析出与折射率调控及其在光开关、波分复用、波导型有源器件、光子晶体等微光学器件的制备及光学集成领域应用的进展．     

飞秒激光与晶体材料相互作用的研究进展

综述了飞秒激光与各种晶体材料作用的现象,如双光子、多光子非线性吸收致上转换发光现象,各类微结构、色心结构等;阐述了飞秒激光与各种晶体的作用机制及在各方面的应用;展望了飞秒激光与晶体材料作用的应用前景.     

Ti:Fe:LiNbO_3晶体的生长及其光折变性能的研究

采用熔体提拉法生长了不同掺杂浓度的Ti：Fe：LiNbO3晶体．研究了掺杂杂质离子浓度变化对晶体光折变性能的影响，测定了晶体经热化学还原处理前后的透射谱．用ESR方法证实，未经还原处理时，Ti：Fe：LiNbO3晶体中Ti离子以Ti4 形式存在．与Fe：LiNbO3和Ti：LiNbOa相比，Ti、Fe复合掺杂，通过电荷补偿效应，使未经还原处理的晶体中Fe2 增加，从而使光吸收增强；可以通过改变Ti、Fe掺杂浓度的方法来控制晶体中Fe2 离子的浓度，达到控制并改善晶体光折变性能的目的．本文还对Ti：Fe：LiNbO3晶体的全息性能进行了研究，测得Ti：Fe：LiNbO3晶体响应时间缩短，衍射效率高达90％以上．Ti：Fe：LiNbO3晶体是一种优质的光折变材料．     

Eu^3＋：LiNbO3Eu单晶的坩埚下降法生长及其光谱性质

选用合适的温度梯度(20～30℃／cm)与生长速度(1～3mm／h)，用坩埚下降法成功地生长出了掺杂Eu^3 的LiNbO3单晶。用X射线衍射及DTA分析表征了获得的晶体。生长的晶体无宏观缺陷，在He-Ne激光的照射下，无散射中心。测定了从生长初期下部到生长后期上部晶体的紫外一可见吸收光谱与荧光光谱。观测到分裂的光谱线。结果表明，沿着晶体生长方向，Eu抖浓度逐步减少。Eu抖离子在晶体中取代Li与Nb格位。     

掺锌铌酸锂晶体的拉曼光谱

为研究LiNbO3晶体中Zn2 浓度对拉曼光谱的影响,以及Zn2 在LiNbO3晶体中的占位和Zn:LiNbO3晶体的结构,分别在LiNbO3中掺进摩尔分数为0.02、0.04、0.06、0.08 ZnO的Zn:LiNbO3晶体,进行其A1(To)和E(To)模的拉曼光谱测试.结果表明,当掺杂ZnO的摩尔分数小于0.06时,拉曼光谱变化不大,当掺杂ZnO的摩尔分数大干8%时,晶体拉曼光谱的274 cm-1峰变得模糊,E(To)模也混入A1(To)模中,晶体峰值变化较大.     

云母微晶玻璃等温转变动力学的研究

本文对以TiO₂为晶核剂的云母微晶玻璃等温析品转变进行了研究,发现玻璃的差热分析（DTA）曲线上出现了两个析晶放热峰,X光衍射分析（XRD）表明,在这两个析晶峰温度下从玻璃中分别析出了钛酸镁（MgTi₂O₅）和云母（KMg₃AlSi₃O₁₀F₂）晶体.用差热分析测定了玻璃等温析晶活化能和晶体的生长指数．玻璃析出钛酸镁和云母的活化能分别为242kJ／mol和265kJ／mol．云母晶体以二维方式生长,生长过程受界面过程控制.     

硅基LiNbO3薄膜的微结构研究

利用透射电子显微镜及X射线衍射，研究脉冲激光沉积技术(PLD)在Si(001)衬底上生长LiNbO3薄膜的微结构．结果表明，在600℃的衬底温度、30Pa的氧分压条件下，在硅片表面5nm厚的非晶氧化层上生长的薄膜，为c轴择优取向的单相LiNbO3晶体，本文还讨论了获得c轴择优取向LiNbO3薄膜的生长机理．     

Eu3+:LiNbO3单晶的坩埚下降法生长及其光谱性质

选用合适的温度梯度(20～30℃/cm)与生长速度(1～3mm/h),用坩埚下降法成功地生长出了掺杂Eu3+的LiNbO3单晶.用X射线衍射及DTA分析表征了获得的晶体.生长的晶体无宏观缺陷,在He-Ne激光的照射下,无散射中心.测定了从生长初期下部到生长后期上部晶体的紫外-可见吸收光谱与荧光光谱.观测到分裂的光谱线.结果表明,沿着晶体生长方向,Eu3+浓度逐步减少.Eu3+离子在晶体中取代Li与Nb格位.     

Application of femtosecond-laser induced nanostructures in optical memory

The femtosecond laser induced micro- and nanostructures for the application to the three-dimensional optical data storage are investigated. We have observed the increase of refractive index due to local densification and atomic defect generation, and demonstrated the real time observation of photothermal effect after the femtosecond laser irradiation inside a glass by the transient lens (TrL) method. The TrL signal showed a damped oscillation with about an 800 ps period. The essential feature of the oscillation can be reproduced by the pressure wave creation and propagation to the outward direction from the irradiated region. The simulation based on elastodynamics has shown that a large thermoelastic stress is relaxed by the generation of the pressure wave. In the case of soda-lime glass, the velocity of the pressure wave is almost same as the longitudinal sound velocity at room temperature (5.8 microm/ns). We have also observed the localized photo-reduction of Sm3+ to Sm2+ inside a transparent and colorless Sm(3+)-doped borate glass. Photoluminescence spectra showed that some the Sm3+ ions in the focal spot within the glass sample were reduced to Sm2+ ions after femtosecond laser irradiation. A photo-reduction bit of 200 nm in three-dimensions can be recorded with a femtosecond laser and readout clearly by detecting the fluorescence excited by Ar+ laser (lambda = 488 nm). A photo-reduction bit can be also erased by photo-oxidation with a cw Ar+ laser (lambda = 514.5 nm). Since photo-reduction bits can be spaced 150 nm apart in a layer within glass, a memory capacity of as high as 1 Tbit can be achieved in a glass piece with dimensions of 10 mm x 10 mm x 1 mm. We have also demonstrated the first observation of the polarization-dependent periodic nanostructure formation by the interference between femtosecond laser light and electron acoustic waves. The observed nanostructures are the smallest embedded structures ever created by light. The period of self-organized nanostructures can be controlled from approximately 140 to 320 nm by the pulse energy and the number of irradiated pulses. Furthermore, we have also observed the self-assembled sub-wavelength periodic structures created in silica glass by femtosecond pulses on the plane of the propagation of light.     

Formation of void array inside transparent and absorptive glasses by femtosecond laser irradiation

We demonstrate self-fabrication of void arrays in a fused silica transparent in the visible and a color-filter borosilicate glass strongly absorptive at 800 nm using tightly focused Ti-sapphire femtosecond laser pulses at 1 kHz without scanning. The period, the size, the number of voids, and the length of the aligned void structure were controlled by changing the laser pulse energy, and the position of the focal point inside two materials. The void arrays were observed by an optical microscope and also estimated by an optical diffraction experiment. The void size and period were smaller in the absorptive glass than in the transparent glass. The submicrometer-sized void was observed by a scanning electron microscope. The smaller and clearer void arrays were formed in the color filter than the fused silica glass. With increasing the laser focal depth, the void-array length increased in the fused silica and decreased in the color filter.     

Infrared femtosecond laser pulse-induced three-dimensional bright and long-lasting phosphorescence in a Ce3+-doped Ca2Al2SiO7 crystal

We report on three-dimensional bright and long-lasting phosphorescence in a Ce(3+)-doped Ca(2)Al(2)SiO(7) crystal. After we scan with a focused 800-nm femtosecond pulsed laser, the path traversed by the focal point of the laser in the crystal emits bright and long-lasting phosphorescence that can be seen with the naked eye in the dark even 10 h after the removal of the activating laser. Absorption spectra of the crystal show that defect centers have formed after the laser irradiation, and the absorption that is due to the defect centers decays with time. It is suggested that a mechanism of the long-lasting phosphorescence consists of a thermostimulated recombination of holes and electrons at traps induced by the laser irradiation at room temperature.     

Silicon precipitation via photoinduced reaction using femtosecond laser

Silicon precipitation inside a glass is an important technique for silicon photonics. We successfully precipitated silicon inside silicate glasses containing an Al metal film using femtosecond laser irradiation. First, the Al-inserted sandwiched glass was fabricated by the direct bonding method. The results of a tensile test indicated that the adhesive strength of the sandwich structure reached approximately 4 MPa. Next, femtosecond laser pulses were focused at the Al/glass interface in the sandwich structure. A transmission electron microscopy photograph at the focus of the laser showed that the Al particles were dispersed into the glass substrate to a depth of approximately 2 microm from the initial Al layer. In addition, Raman spectra indicated that silicon had formed at the interface between the glass and Al film after the laser irradiation. The morphology or the particle size of the precipitated silicon was successfully modified by changing the repetition rate or the pulse energy of the laser.     

Periodic nanovoid structures via femtosecond laser irradiation

We have observed periodically aligned nanovoid structures inside a conventional borosilicate glass induced by a single femtosecond (fs) laser beam for the first time, to our knowledge. The spherical voids of nanosized diameter were aligned spontaneously with a period along the propagation direction of the laser beam. The period, the number of voids, and the whole length of the aligned void structure were controlled by changing the laser power, the pulse number, and the position of the focal point.     

Effect of MgO doping of periodically poled lithium niobate on second-harmonic generation of femtosecond laser pulses

We theoretically analyze type-I broadband second-harmonic generation (SHG) of femtosecond laser pulses based on a quasi-phase-matching configuration in periodically poled congruent LiNbO3 (LN) andperiodically poled MgO:LiNbO3 (PPMgLN) (5% and 7%). Group-velocity matching (GVM) can be achieved at the fundamental waves of 1.59, 1.56, and 1.55 microm for SHG when the three types of crystals have grating periods of 22.31, 20.07, and 23.45 microm, respectively. It is found that the central wavelength of the fundamental wave for GVM will increase with the decrease of MgO doping in LN. It is concluded that the shift of the GVM central wavelength is due to the difference of MgO doping, which changes the dispersion of the crystal. Therefore, tunable and high efficiency broadband SHG of femtosecond laser pulses in a long crystal can be realized by selecting different doping rates of PPMgLN.     

Failure mechanism of optically transparent solids subjected to a local thermal laser pulse

Experimental data on the failure mechanism of glass plates subjected to a millisecond pulse of focused laser light are presented. It is established as a result of investigation of the failure kinetics of irradiated glass plates that their failure is caused by an increase in gas pressure in the cavity formed at the focal point of the light-collecting lens. This failure mechanism of glass differs from that described earlier for the case of the irradiation of a glass plate by a nanosecond pulse of laser light, according to which the glass fails as a result of the development of a high-amplitude acoustic pressure wave near the front surface of the irradiated plate. The failure mechanism described for the glass plates agrees with a thermodynamic failure model of transparent solids.Translated from Problemy Prochnosti, No. 4, pp. 88–93, April, 1993.     

Catalytic three-dimensional protein architectures

We demonstrate a strategy for microfabricating catalytically active, three-dimensional matrixes composed of cross-linked protein in cellular and microfluidic environments. In this approach, a pulsed femtosecond laser is used to excite photosensitizers via multiphoton absorption within three-dimensionally defined volumes, a process that promotes cross-linking of protein residue side chains in the vicinity of the laser focal point. In this manner, it is possible to fabricate protein microparticles with dimensions on the order of the multiphoton focal volume (less than 1 microm(3)) or, by scanning the position of a laser focal point relative to a specimen, to generate surface-adherent matrixes or cables that extend through solution for hundreds of micrometers. We show that protein matrixes can be functionalized either through direct cross-linking of enzymes, by decoration of avidin matrixes with biotinylated enzymes, or by cross-linking biotinylated proteins that then are linked to biotinylated enzymes via an avidin couple. Several formats are explored, including microparticles that can be translocated to desired sites of action (including cytosolic positions), protein pads that generate product gradients within cell cultures, and on-column nanoreactors for microfluidic systems. These biomaterial fabrication technologies offer opportunities for studying a variety of cell functions, ranging from single-cell biochemistry and development to perturbation and analysis of small populations of cultured cells.     

LiNbO_3晶体在凝胶玻璃中的受控析晶研究

采用Ｓｏｌ－ｇｅｌ工艺,以Ｎｂ（ＯＨ）５为铌酸盐的起始原料,低温合成了ＬｉＮｂＯ３／ＳｉＯ２凝胶玻璃。通过ＤＴＡ、ＸＲＤ和ＩＲ分析方法,研究了ＬｉＮｂＯ３晶体在凝胶玻璃中的析晶过程和析晶动力学。结果表明,ＬｉＮｂＯ３微晶在凝胶玻璃中的析晶过程是受界面控制的,其析晶活化能为１４２ＫＪ／ｍｏｌ。