ns脉冲激光对K9玻璃的破坏实验

采用高速PIN光电探测器和高带宽的数字存储示波器,实时检测透射光脉冲和散射光脉冲的变化特征,并将之用作材料破坏的光学判据,测量得到K9玻璃在1.06μm纳秒脉冲激光作用下的能量损伤阈值约18mJ,相应的能量密度阈值为1.0kJ/cm2。通过分析透射光脉冲和散射光脉冲的特征,给出了材料的破坏时刻,并推断出K9玻璃所能承受的极限光强为1015W/m2。研究了能量透过率与泵浦能量的关系,并初步探讨了透明材料的破坏机理。结果表明:在多纵模激光的作用下,透明光学材料破坏是电离击穿与自聚焦效应综合作用的结果。     

不同材料的受激布里渊散射特性

 采用波长为1.064, 0.532 μm的聚焦高斯光束作为泵浦光,数值求解受激布里渊散射（Stimulated Brillouin Scattering, SBS）放大器型耦合波方程组,比较K9玻璃、熔石英、BK7玻璃、CaF₂的SBS特征参数。研究发现：对于相同的激光参数,不同的介质具有不同的SBS特征,声子寿命长则破坏阈值低,破坏效果明显。SBS过程对CaF₂的破坏效果较明显,导致了介质前表面的破坏,在一定的激光参数和聚焦参数下,焦点附近优先于前表面破坏。SBS过程可以得到脉宽压缩比大于10、强度比泵浦光峰值高5倍以上的Stokes散射光脉冲。相同激光参数下,不同材料压缩效果及散射光相位共轭保真度不同,CaF₂在低泵浦能量时脉宽压缩特性较好;高泵浦能量时,相位共轭保真度较好。固体透明光学材料中可获得大于95%的能量提取效率。     

对超短脉冲激光引雷产生的等离子体通道的特性分析

 利用隧道电离诱导闪电模型,对超短脉冲激光在大气中产生弱等离子体通道的电阻和阈值强度进行了分析和计算。结果显示：强度为10¹⁴ W/cm²量级的超短脉冲激光产生的气体等离子体通道有较好的导电性,所需激光能量很小, 说明在该模型下激光能量的利用效率很高。     

C60/PMMA复合材料的反饱和吸收与光限幅特性研究

本文报导C₆₀/PMMA复合材料的制备方法,并采用调QNd:YAG倍频脉冲激光照射C₆₀/PMMA夏合材料,研究了其反饱和吸收与光限幅将性。在线性透射率为46%条件下,光限幅阈值能量密度为65mJ/cm²,材料破坏能量密度阈值为600mJ/cm².与C₆₀甲苯溶液相比具有一定的优点。     

1.06μm连续激光照射下K9玻璃板的应力松驰破坏

 基于一维应力松弛模型和粘弹性本构关系,对1.06μm连续激光照射下K9玻璃板中的温升和应力作了计算,结果表明,由于应力松弛效应,激光停照后的冷却过程中产生的残余拉伸应力可达到玻璃的拉伸断裂强度阈值,而激光加热期间的最大压缩应力却小于压缩断裂强度要求。对3mm厚的K9玻璃板,由应力松弛引起破坏所要求的激光参数为946kWm^-2作用0.2s,因而应力松弛可能为1.06 μm连续激光大光斑照射下K9玻璃窗口损伤的主要模式。     

透红外含碲氟铝基玻璃的激光损伤阈值

 在氟铝酸盐玻璃组分中加入适量声子能量低的重金属氧化物TeO ₂，得到一种新的氧氟化物玻璃。该材料具有良好的成玻璃性能，适合制作大尺寸红外窗口镜。研究了TeO2含量对玻璃特征温度、阿贝数和红外透过性能的影响。同时测试了这种玻璃的抗DF激光能力，结果表明： TeO ₂含量为15%的玻璃，DF激光破坏阈值达14.95 kＷ·cm^-2。分析显示，由于玻璃基质的多声子吸收，对激光能量的吸收而引起的热冲击是导致玻璃破坏的主要原因。进一步降低玻璃中水分，可以提高玻璃抗激光破坏性能。     

飞秒激光激发空气电离的阈值研究

报道在脉宽50fs—22ps，波长800nm脉冲激光作用下的空气电离阈值的研究结果.利用探测等离子体发光信号的方法，实验测量了激发空气电离所需的阈值激光强度.结果表明，当激光脉冲宽度从50fs增加到22ps时，阈值光强I_th从8.7×10¹⁴W/cm²下降到2.7×10¹³W/cm²；I_th经历了由迅速降低逐渐发展为缓慢降低的过程.在50fs—1p     

飞秒激光作用下全向高反膜破坏的激发过程

设计和制备了全向高反膜SiO₂/TiO₂，研究了它在不同脉冲宽度、不同脉冲能量的飞秒激光作用下的破坏阈值和烧蚀深度.利用发展的抽运-探针方法，研究了抽运脉冲作用下材料中导带电子的超快激发和能量沉积过程，建立并求解了飞秒激光激发材料和材料的激发对抽运光自身反作用的耦合动力学模型.模型较好地揭示了材料破坏的激发过程. 关键词： 飞秒激光 全向高反膜 激发过程 破坏机制     

超短脉冲激光照射下氧化铝的烧蚀机理

利用烧蚀面积与激光脉冲能量的线性关系，确定了氧化铝的破坏阈值，同时采用散射光探测法，研究了800和400nm超短脉冲激光作用下氧化铝的破坏阈值对激光脉宽的依赖关系，并探讨了氧化铝的烧蚀规律. 利用雪崩击穿模型，解释了实验结果，并讨论了导带电子光吸收机理. 关键词： 飞秒激光 氧化铝 破坏阈值 雪崩模型     

多脉冲激光对K9玻璃的表面损伤实验研究

 实验研究了波长为1 064 nm、脉宽为10 ns、重复频率为1 Hz的激光脉冲对K9玻璃的表面损伤特点,给出了脉冲透过能量随激光脉冲作用次数变化的规律。采用3维立体显微镜对损伤形貌进行观察,发现K9玻璃的损伤表面呈环状分布,分为烧蚀区、微裂纹区和断裂区。随着激光脉冲个数的增加,损伤由点状破坏演变为损伤区,微裂纹逐渐增长,损伤面积逐渐增大。基于激光支持的爆轰波理论分析,激光与脆性材料的相互作用可引起微裂纹的大量增长。在多脉冲激光的作用下,K9玻璃损伤的累积效应明显,表面损伤阈值明显降低,表面裂纹增长明显,损伤面积逐渐增大;但随着激光脉冲的继续增加,这种损伤趋于稳定。     

Energy transmissivity of high-power nanosecond laser pulse focused on glass

The experimental results show that if the pulse energy is low, the damage does not occur and the corresponding transmissivity is 100%. But with the increase of the pulse energy, the damage occurs and the transmissivity decreases to between 100% and 50%, equal to 50% and lower than 50%.The concept of the cut-off time (T_cut) is proposed to give the physics explanation on it, and by taking the free electron density (FED) and the laser-induced damage threshold (LIDT), mathematical simulation of the change law of the T_cut and the corresponding energy transmissivity with the laser energy has been done, respectively. The analysis results indicate that the former definition method can predict all the situations successfully, but the second one cannot predict the situation of the transmissivity being between 100% and 50%, the reasons of this difference also be analyzed.     

Ultrafast dynamics in ZnO thin films irradiated by femtosecond lasers

The damage morphologies, threshold fluences in ZnO films were studied with femtosecond laser pulses. Time-resolved reflectivity and transmissivity have been measured by the pump-probe technique at different pump fluences and wavelengths. The results indicate that two-phase transition is the dominant damage mechanism, which is similar to that in narrow band gap semiconductors. The estimated energy loss rate of conduction electrons is 1.5 eV/ps.     

汽车太阳膜的色度与光谱特性分析

通过用带计算机控制的WGS-9型色度测量系统、UV-Vis 8500型双光束紫外-可见分光光度计和WGD-4A型光栅光谱仪定量测量和分析了某品牌汽车太阳膜的色度和光谱特性。测量分析结果表明：低红外透过率和紫外透过率与高可见光透过率是一对矛盾体,在选择太阳膜时只能有所侧重。如要求较高可见光透过的同时要避免过多紫外线照射,那应选择主波长为587.3 nm(浅蓝)或522.1 nm(钻石绿)的太阳膜。如要求较高可见光透过同时要兼顾隔热节能的功能,那么应选用色度主波长为497.3 nm(宝石蓝)或507 nm(翡翠绿)的太阳膜。     

面向光学器件透反射率测量的声光调制型激光功率稳定系统设计

在各类光学系统设计过程中,由于实验系统对于光学器件的透反射率要求不同,需要确定光学器件的透反射率。本文设计了一种对光学器件的透反射率进行精准测量及标定的系统,该系统通过对激光光源进行声光调制,使得激光输出功率的稳定度显著提高,避免了测量时光源不稳定带来的较大误差。实验结果表明,该系统能够稳定光源输出功率,稳定度维持在0.05%/h,甚至更高的水平,满足了光学器件透反射率测量的误差小,精度高等要求。     

LCD三基色光谱特性的研究

用分光光度计测量TB3639型液晶光阀在电压和频率两种驱动方式下的电光特性关系曲线,分析在这两种驱动方式下液晶对三基色的透射率变化情况;结果表明,三基色在两种驱动方式下,其透射率的变化并不一致,显示的图像会有一些偏色,这对显示质量的影响较大。在电压驱动方式下,随着电压变化,液晶对三基色透射率变化的不一致性更为显著,差值最大为11％,最小为0％。在频率驱动方式下,透射率差值相对较小,差值最大为4％,最小为2.5％,三基色透射率变化有更好的一致性。以此作为基础,对颜色进行一定的校正和补偿,以获得精确的色调和色饱和,便于进一步研究改善液晶显示性能。     

Adaptive optical properties of ER fluid incorporating composite particles

Electrorheological (ER) fluid is one of the popular materials used in smart materials and structures. The material properties of ER fluid can be changed markedly while an external electric field is imposed on ER fluid domain. In this paper, the optical properties of ER suspensions consisting of composite particles dispersed in silicone oil are investigated. Both dc and ac electric fields are utilized to be imposed on ER fluid. The transmissivity of light through ER fluid under various electric fields is detected and analyzed. It is shown that the transmissivity of light increases with the increasing electric field strength and time. The change of transmissivity is caused by the formation of particle chains. The higher the particle concentration, the faster the change occurs. When an ac electric field is applied, the transmissivity can be affected by the frequency of electric field.     

Calculation of the absorption coefficients of optical materials by measuring the transmissivities and refractive indices

In this paper, a formula for accurate calculation of the absorption coefficient of optical material is deduced by the relationship of its transmissivity, refractive index and absorption coefficient. Because the values of transmissivity and refractive index of the optical material with a higher accuracy can be determined by the instruments or obtained directly from the references, the calculated results of the absorption coefficients with a higher accuracy is certified. The absorption coefficients of some optical materials are calculated with it, and the results are discussed.     

The effect of microscopic features upon the transmissivity of enclosed laser ablated laminated metallised polymer films

A vacuum-deposited aluminium layer (20 nm) is sandwiched between two layers of laminated oriented polypropylene (OPP) film whose thickness varies from 20 to 40 μm. Selected areas of this sealed system were transparentised by the redistribution of the aluminium layer without breaking the seal or causing damage to the OPP film using a 75 W Q-switched Nd:YAG laser. The resultant transparentised films contain aluminium particles, distorted polymer areas and intact areas of the vacuum-coated aluminium layer. This paper investigates the effect of microscopic features upon the overall transmissivity of the laser-treated films and hence the quality of the transparentisation process.     

微通道板2.0～5.5 keV X射线透过率标定

 在北京同步辐射3B3中能X射线束线2.0~5.5 keV能段对微通道板(MCP)透过率进行了测量标定。实验表明,MCP在2.0 keV的低能段处和5.5 keV的高能段处的透过率较高,而中段较低。对MCP透射和X光在MCP毛细导管列阵中的全反射两种机制进行了物理建模,分别计算验证。结果发现:X光在毛细导管内掠入射会产生全反射,且能段越低反射率越高;MCP透过率特性正是MCP特殊的结构和材料造成的,为透射和反射两种机制共同贡献的结果,低能端主要来自X光在毛细导管中的全反射贡献,高能端主要来自透射贡献。     

可实现偏振无关单向传输的二维硅基环形孔光子晶体

基于光子晶体来构筑偏振无关光二极管在光电集成领域具有重大的应用价值.首先提出了一种环形孔光子晶体,能带结构显示其对横电及横磁模式同时展现出显著的方向带隙.以此构建了三角形状的环形孔光子晶体,利用时域有限差分法计算其透过谱及场分布图,发现该结构能实现偏振无关单向传输特性,然而正向透过率太低(约20%).进一步引入尺寸较小的三角形状的环形孔光子晶体构成光子晶体异质结结构,有效地提高了偏振无关单向传输性能,正向透过率增大了一倍.通过界面结构的调整,正向透过率进一步增大,优化后的环形孔光子晶体异质结结构能同时对类横电及类横磁模式入射光实现单向传输,且正向透过率达到了44%.