Laser Mode-Dependent Size of Plasma Zones Induced by Femtosecond Laser Pulses in Fused Silica

We carry out the numerical simulations of femtosecond laser propagation with TEMoo mode, TEM10 mode and a beam combining both the modes in fused silica. It is found that the transverse size of plasma zones induced by laser pulses with the TEM10 mode is smaller than that induced by the TEM00 mode, while the longitudinal size is almost the same, and the saturated plasma density is higher. The transverse size, the longitudinal size and the ratio of the longitudinal to transverse size, for the beam combining both the modes, all could be reduced at the same time in comparison with the TEM00 mode under the same focusing conditions.     

Diagnose Parameters of Plasma Induced by Femtosecond Laser Pulse in Quartz and Glasses

Electron plasma induced by a focused femtosecond pulse (130 fs, 800 nm) in quartz, fused silica, K9 glass, and Soda Lime glass was investigated by pump-probe technology. Pump and probe shadow imaging and interferometric fringe imaging have been used to determine plasma density, relaxation time, and electron collision time in the conduction band. In these materials, the electron collision time is about several femtoseconds when the electron density is in the 10¹⁹cm⁻³ range. The electron relaxation processes are different: lifetime is about 170 fs in pure quartz and fused silica, and about 100 ps in K9 and Soda Lime glass. The modified electron band by doped ions is regarded to be responsible for the difference of decay time in these materials.     

Bubble Generation in Germanate Glass Induced by Femtosecond Laser

We report the observation of bubble generation and migration in a germanate glass during irradiation by a femtosecond laser of high repetition rate.Bubbles are formed around the focal area of the laser beam,and their movement indicates the presence of thermal gravity convection in the glass melt,which is beyond the existing theoretical model about temperature field of focal area.Inside the bubbles,oxygen molecules are observed by the confocal Raman micro-spectroscopy.The generation of molecular oxygen and bubbles is explained in terms of the spatial separation of Ge and O ions and micro-explosion inside the glass melt.     

Nuclear Excitation by X-Ray Emission of Femtosecond Laser Plasma

The proposed model of laser plasma emission spectrum formation enables us to determine the absolute value of the laser pulse to plasma emitted radiation conversion factor, profile of the emission spectrum, and frequency distribution of the intensity and energy in the emitted spectra. This is of interest for laser plasma diagnostics and provides a means for direct calculation of the number of excited nuclei in dependent on the parameters of laser pulse. This revised version was published online in August 2006 with corrections to the Cover Date.     

飞秒激光辐射诱导金属表面微纳结构研究

通过1 kHz的飞秒脉冲(脉宽130 fs,中心波长800 nm)对厚度为60 μm的不锈钢65Mn表面进行飞秒微加工,通过拟合得到65Mn的消融阈值为0.5 J·cm-2。研究了飞秒激光作用下表面形成的多种微结构,其中包括纳米孔及纳米柱状物。同时讨论了激光能量和作用脉冲个数对微结构形成的影响。随着周期波纹结构的形成,发现在各种能量和脉冲个数条件下,周期结构的周期约为入射脉冲的波长。相同的激光功率下,在不同加工速度和加工次数下对不锈钢进行表面微加工,得到了规则的圆孔阵列结构。     

外加高压电场下空气中激光等离子体通道寿命研究

通过对飞秒激光在空气中产生的等离子体通道两端外加高压,来研究通道的寿命变化情况。实验得到,当在等离子体通道两端外加高压时(350 kV/m),等离子体通道寿命延长了近3倍。理论模拟和分析结果表明在外加电场条件下,碰撞电离得到增强,吸附作用相对减弱,解离复合系数随着电子平均能量的增加而下降的趋势更为剧烈,这进一步引起了等离子体通道寿命的延长。实验结果与理论分析共同表明了利用外加电场对空气中激光等离子体通道寿命进行延长的可行性。     

靶材对激光等离子体诱导靶上电势信号的影响

将高功率脉冲激光分别作用于Cu、Fe、Al三种金属靶材,通过实验测试激光等离子体在这三种金属靶上产生的电势信号,讨论了靶材料对电势信号的影响.实验结果表明：靶上电势信号早期阶段受靶材料的影响比较显著,早期信号峰值大小随靶材变化顺序依次为：IFe>ICu>IAl,而峰值到达时间依次为：tAl相似文献   

飞秒激光作用下光学与激光玻璃的暗化阈值测量

报道了各种商用光学玻璃和激光玻璃在800nm、120fs、1kHz钛宝石脉冲激光作用下,产生光致暗化的阈值。     

时空分布的超短激光脉冲烧蚀电介质材料时等离子体的产生

若考虑聚焦平面内固定区域,脉冲空间分布可简化为一维问题.在此基础上,从脉冲的传输过程出发,本文分析了时空分布的超短激光脉冲与电介质材料相互作用时等离子体形成模式.在材料内部累积的能量与脉冲宽度、与空间相关的损伤区域、等离子体形成时间及其吸收系数有关.     

Sub-wavelength Ripple Formation on Silicon Induced by Femtosecond Laser Radiation

Periodic microstructures on silicon bulk axe formed by the irradiation of the femtosecond laser with the laser wavelength of 800 nm and the pulse length of 130 fs. We investigate the surface periodic ripple structures produced by femtosecond laser treatment. The effects of feedrate of sample, v, on laser-induced surface topography are studied. We find that the femtosecond laser produce periodic ripples of the sub-micron level on silicon surface. At the same time, we realize the optimal conditions to produce these surface structures. When choosing NA = 0.3, and v = 2000μm/s or 3000μm/s, we find a series of periodic-structure ripples where the spacing is about 120 nm and the width is about 45nm. The experimental results indicate that femtosecond laser treatment can produce line arrays on the sub-micron level, which is a positive factor for fabricating grating and other optical applications in nanoscales.     

Diagnostics of Dielectric Materials with Several Relaxation Times

Technical Physics - A set of means for detection and preprocessing of dielectrometric information has been suggested for studying the polarization/depolarization of dielectrics. Special attention...     

Self-Assembled Quasi-Periodic Voids in Glass Induced by a Tightly Focused Femtosecond Laser

Multiple refocusing of a tightly focused femtosecond laser due to the dynamic transformation between self-focusing and self-defocusing is employed to provide a novel method to produce quasi-periodic voids in glass. It is found that the diameter or the interval of the periodic voids increases with the increasing pulse energy of the laser. The detailed course for producing periodic voids is discussed by analysing the damaged track induced by the tightly focused femtosecond laser pulses. It is suggested that this periodic structure has potential applications in fabrication of three-dimensional optical devices.     

飞秒激光诱导玻璃内析出BaTiO3晶体

使用800nm、120fs、200kHz的高重复频率超短脉冲激光照射BaO-TiO2-SiO2系玻璃，玻璃经飞秒激光照射数秒钟后，激光会聚点的发光由800nm波长的红色突然转变为非常强的400nm的蓝色，对激光辐照点的发光光谱和X射线衍射分析表明，具有倍频效应的BaTiO3晶体已经产生。     

Femtosecond Laser Induced Rewritable Optical Memory in Silicate Glasses

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Femtosecond Laser Induced Rewritable Optical Memory in Silicate Glasses

A novel method for producing rewritable optical memory with ultra-high storage density and ultra-high recording and readout speed is presented. A 120 fs, 800 nm, 1 kHz laser focused by an objective lens is used to produce recording bits in glass with high transmittance contrast. These recording bits can be erased by heat-treatment. The mechanism has been discussed by means of the absorption and electron spin resonance(ESR) spectra of silicate glasses before and after irradiation by the laser. The absorption of glasses increases greatly after irradiation because of color-center generation through multi-photon absorption. ESR spectra shows that the color-center induced in the glass are hole-trapped defects. The color-center disappears when the glass heated because the holes and electrons at traps are released by thermal stimulation and recombine again.     

On the Laser Induced Synthesis of Dense Hydrogen

The proposal, synthesis of dense hydrogen using Hp molecules in different electronic states, is partly supported by the potential energy calculations and the rate equation analy&. Using a simple model of the screened hydrogen molecules,. the reduction of metallization pressure arising from the electron-hole pair is estimated for solid hydrogen. The result is more reasonable and in agreement with Rose comments.     

Estimation of the Refractive Index Change in Glass Induced by Femtosecond Laser Pulses

It is known that local refractive index change occurs when femtosecond laser pulses with extremely high peak power are launched into glass. We focused 130-femtosecond laser pulses of 800 nm into the bulk of glass and examined the shape of the induced refractive index change. We found that the length of the spot of the refractive index change along the optical axis reached about 30 μm despite the diameter being about 2 μm. To estimate the distribution of induced refractive index change, we fabricated Bragg grating by scanning the focused spot and calculated the amount of the change by applying Kogelnik’s coupled mode theory to the measured diffraction efficiencies of the higher order diffracted beams.     

飞秒激光在6H SiC晶体表面制备纳米微结构

激光诱导周期性纳米微结构在多种材料包括电介质、半导体、金属和聚合物中观察到。研究了800nm和400nm飞秒激光垂直聚焦于6H SiC晶体表面制备纳米微结构。实验观察到800nm和400nm线偏光照射样品表面分别得到周期为150nm和80nm的干涉条纹,800nm圆偏振激光单独照射样品表面得到粒径约100nm的纳米颗粒。偏振相互垂直的800nm和400nm激光同时照射晶体得到粒径约100nm的纳米颗粒阵列,该纳米阵列的方向随400nm激光强度增加而向400nm偏振方向偏转。利用二次谐波的观点对以上纳米结构的形成给出了解释。     

飞秒和纳秒激光脉冲作用下等离子体X射线辐射特性

对飞秒和纳秒激光作用下的Ａｌ和Ｃｕ等离子体的Ｘ射线辐射进行了测量、分析和比较．实验结果表明在飞秒激光脉冲下等离子体Ｘ射线峰值向短波方向移动．同时Ａｌ等离子体的的电离阶数和温度在飞秒下比纳秒高．