周期自洽的充氢溴化亚铜激光动力学模型

建立了一个比较完整的、周性性自洽的充氢溴化亚铜激光动力学模型,获得了激光工作物质粒子数、激光光强、电子温度、电子密度等一系列参量的时空分布与变化,并与实验值作了比较. 关键词：     

激光技术产业发展战略与战术专题讲座在汉举行

正2013年12月26日,激光技术产业发展战略与战术专题讲座在汉举行。湖北省政协副主席、省科技厅厅长郭跃进以及来自武汉·中国光谷激光行业协会、湖北省暨武汉激光学会会员单位的80余名企业家、科技工作者等出席专题讲座。郭跃进从"激光产业问题及解决的措施"、"产业链创新体系建设"、"激光产业技术研究院建立"、"我省如何加快激光产业发展"等四个方面讲解了我省激光技术产业发展战略与战术。他说,湖北省委、省政府高度重视激光产业的发展,主要领导曾多次深入激光企业进行调研,近日,省     

激光空泡特性实验与数值计算研究

基于激光空泡内物质以水蒸气为主的特征,选择特定的Rayleigh-Plesset方程形式,确定激光空泡的动态泡壁位置,并考虑水中气体与激光空泡之间的质量扩散、水蒸气的凝结与蒸发、水的压缩性及热传导、声辐射、黏性、表面张力等因素.建立激光空泡的产生、照相和声压测量系统.通过数值计算与实验结果相结合的办法,使泡内压力的计算值与实验值之间相对误差控制在10%以内,揭示吸收的激光脉冲能量与激光空泡的半径、泡内压力和温度之间的对应关系,以及吸收的激光脉冲能量不变时半径、压力和温度的变化规律.旨在为激光空泡的相关研究提供一定的参考. 关键词： 激光空泡 水蒸气 数值模拟 Rayleigh-Plesset方程     

激光辐照受载金属软化效应的数值模拟

用有限元法模拟了连续激光辐照受载金属所产生的软化效应。建立了计算软化效应的二维有限元数值模型。得到了软化效应与预载荷、激光功率密度的依赖关系。结果表明,激光产生的软化效应会大大降低金属材料的屈服阈值,且材料的软化程度与预载荷及激光功率密度有关。     

基于微通道板的单光子激光测高技术研究

与传统的激光测高技术相比,单光子激光测高技术具有数据量大、质量轻、测距精度高等优势,是激光测高技术的发展趋势。建立数学模型对单光子激光测高特性进行研究,用数值计算估计了单光子激光测高的性能,并建立了地物模型,用蒙特卡罗方法进行了仿真,提出了测高数据的滤波方法和一种利用遥感图像优化高程信息的算法。结果表明:在正午阳光背景最强烈的条件下,典型地物模型单光子激光测高的均方根误差为6.1cm,用算法优化后的误差为2.6cm。     

激光场中H原子多光子电离速率

建立了激光与原子相互作用的伪分立态模型,并用此模型计算了激光场中Ｈ原子的多光子电离速率。对于光子能量较小的激光,计算结果与其它理论计算结果相符合。     

激光对反舰导弹红外探测器干扰分析

针对激光对红外制导的反舰导弹干扰问题,建立了激光对反舰导弹红外探测器的干扰链路模型,推导了激光海上传输的大气透过率,计算了1．06μm激光在海上大气传输时仰角、能见度与大气透过率的关系,估算了对不同距离的反舰导弹红外探测器实现有效干扰所需发射的激光能量。     

激光场中H原子的多光子电离速度

 建立了激光与原子相互作用的伪分立态模型,并用此模型计算了激光场中H原子的多光子电离速率。对于光子能量较小的激光,计算结果与其它理论计算结果相符合。     

半导体激光器混沌法拉第效应控制方法

提出了外腔延时反馈半导体激光器法拉第效应控制下的新激光系统, 构造出两种类型结构光路, 建立了法拉第效应控制下的延时负反馈、延时正反馈激光动力学物理模型, 研究了激光混沌控制与反控制等. 利用法拉第效应原理及磁致旋光性和系统特点, 调节控制光路中的光旋转角度和光延时间可实现双参数控制激光器, 控制激光到双周期、三周期及多周期, 使激光产生拍动等现象, 反控制激光周期到混沌等. 发现了以磁致旋光角分布的激光混沌控制与反控制区域. 并研究了激光混沌控制与周期控制的动态情况, 演示讨论了激光态的转化演变过程等.     

光学窗口材料激光辐照热-力效应的解析计算研究

建立了高功率连续激光辐照透明光学材料的热力学模型,通过积分变换方法求解三维热传导方程,得出了激光辐照引起的瞬态温度场分布的精确解析解,并在此基础上进一步求得热应力场的瞬态分布。以1.315μm的高能氧碘激光辐照熔石英玻璃为例,计算了熔石英在激光辐照下的温度场与热应力场分布,分析了其激光损伤机理。研究结果表明由于熔石英具有优良的热稳定性,温度不均匀分布所产生的热应力相对较小,激光损伤主要是受辐照区域温度值超过材料熔点发生熔融破坏。理论分析结果与相关的实验结论一致,说明所建立激光辐照效应模型的合理性。     

Sub-microdrilling with ultrafast pulse laser interference

A novel sub-microdrilling technique utilising the phenomenon of ultrafast pulse laser interference is reported. This technique overcomes the feature size limit of conventional laser micromachining. The method of first interfering with the laser light, and then using the central bright fringe of the interfered beam to machine has been proven to effectively reduce the effective ablation spot size and, subsequently, to reduce the size of the drilled features. Preliminary results show a 300% reduction in drilled feature size with the interfered laser beam compared with the conventional non-interfered laser beam. 300 nm holes were successfully drilled on a 1000 Å thick Gold film using the interfered laser beam compared to 1 m holes ablated using the conventional non-interfered laser beam at the same pulse energy. PACS 42.62.Cf; 42.15.Eq; 42.25.Hz     

A highly efficient 5 kW peak power Nd:YAG laser with time-shared fiber optic beam delivery

Here, we report on the development of an efficient, high peak power lamp pumped Nd:YAG laser with time-shared fiber optic beam delivery. A maximum average output power of 270 W with 100 J maximum pulse energy and 5 kW peak power has been achieved with an electrical to laser conversion efficiency of 5.4%, which is on higher side for typical lamp pumped solid-state lasers. We have improved efficiency by spectral conversion and water flow optimization in the pump cavity, with a resulting beam quality comparable to commercial systems of similar power level. The resonator has been designed for stable operation from single-shot to 200 Hz repetition rate. A study of pulse-to-pulse laser energy stability for different resonator configurations has also been performed. The resonator was designed to achieve a good beam quality for the whole range of operation with a maximum beam parameter product of 15 mm mrad (M²45). A simple mechanism for time-shared fiber optic port selection has also been devised. Material processing applications such as cutting of stainless steel sheets up to 14 mm thickness and welding of metals such as carbon steel with weld depths up to 2 mm using the developed laser system has also been reported.     

DC-SC光阴极注入器的束载实验的调试进展

 北京大学射频超导实验室设计了新型超导光电子枪——DC-SC光阴极注入器，目标是为自由电子激光平台提供能量在2~3MeV，脉宽小于10ps，脉冲重复频率为81.25MHz，平均流强约为1mA的低发射度电子束。现在已经建成了DC-SC光阴极注入器实验平台，包括激光驱动光阴极系统，Pierce直流高压加速结构，1.3GHz 1＋1/2纯铌超导腔，恒温器低温系统，4.5kW连续波微波系统，1/16分频与同步控制系统，束流诊断系统和能量分析系统等。并且完成了超导腔的静态实验，直流加速结构也经过了100μA低电流测试。实验结果符合设计要求，整体调试后即可以进行束载实验。     

High-contrast all-optical switching with Pt:ethynyl complex

We have theoretically analyzed all-optical switching in Pt:ethynyl complex based on nonlinear excited-state absorption. A detailed analysis for Pt:ethynyl complex has been presented based on rate equation approach. It is shown that a pulsed pump laser beam at 355 nm switches the transmission of a cw probe laser beam at 633 nm through a Pt:ethynyl sample. The effect of various parameters, such as pump pulse width, peak pumping intensity, normalized parameter , transition times of S₁→S₀ and S₁→T₁ states and lifetime of triplet state, on switching characteristics has been analyzed in detail. It has been shown that the probe beam can be completely switched off (i.e. 100% modulation) by a pulsed pump laser beam at 50 kW/cm². These results have been used to design all-optical NOT and the universal NOR and NAND logic gates with multiple pump laser pulses.     

Formation and Transformation of Non‐Bessel Multiring Light Beams

A method for forming multiring light beams (MRLB) on the basis of a biaxial crystal has been developed. The intensity distribution in output MRLBs depending on the parameters of the input light beam has been calculated. For the first time an optical scheme with three axicons for highefficiency transformation of the initial laser beam to a collimated light beam with wavefront dislocation is proposed. The method permits obtaining powerful laser MRLBs which can be used in data transfer and processing systems, in nanotechnologies for manipulating particles, for technological treatment of materials, for acting on organic cells and their components, and for investigating inhomogeneities of transparent media.     

High spatial intensity 10 W-CuBr laser with hydrogen additives

High beam quality output has been demonstrated from a single medium-scale (2 cm dia. × 50 cm) CuBr laser with hydrogen additives. The addition of hydrogen leads to beam divergence reduction and laser power lift-up finally yielding 5-fold increase in laser power spatial intensity compared with the case of no hydrogen added. With a simple positive-branch unstable resonator practical (pulse-average) divergence of 80 rad is achieved. The easy-feasible sealed-off version of CuBr laser makes it an attractive source for many high-quality laser beam applications.     

Temperature measurement during laser heating of thin films using a temperature-sensitive phosphor

A phosphor with temperature-dependent lifetime has been used to measure the temperature distribution produced by laser heating of a thin film surface. A gold thin film deposited on a quartz substrate is coated with 40 m film of the phosphor material. A cw argon ion laser (476 nm) beam is split into two beams, with the more intense beam focused to 15 m (1/e² radius) to heat the film through the quartz substrate. The weaker probe beam is chopped and focused tightly using a microscope objective to excite the phosphor from the other side. The spatial variation in lifetime, and hence the temperature distribution, is obtained by scanning the probe beam over the heated region. The temperature distribution measured for different film thickness's is compared with calculations using a finite element model. The calculated temperatures at the gold surface near the laser beam are higher than the experimentally measured values, and agree only when the heat-sinking effect of the phosphor material is taken into account. The results suggest that a phosphor layer thinner than a micron will be required (for 15 m laser spot size) so as not to perturb the temperature of the gold layer.     

A miniature electron beam pumped laser

The 1.73 μm XeI laser has been operated in a fully continuous mode using a table-top electron beam pumped laser setup. A 12 keV electron beam sent through a 300 nm thick silicon nitride membrane into a laser gas mixture of typically 600 mbar gas pressure was used for pumping. A low loss cavity was installed, resulting in a very low pumping power of 37 mW to reach laser threshold. The geometrical conditions for the laser setup such as the shape of the beam pumped volume and its overlap with the optical mode volume are discussed. The laser scheme has been clearly identified as a recombination laser scheme by operating the laser in pulsed mode and observing the time structure of the laser pulse.     

激光辐照下薄膜镜面波纹损伤机理研究

 用透镜将脉冲激光束聚焦在铝膜镜面上，在部分样品的激光损伤边缘区，出现波纹状损伤形貌。大多数情况下，有多套波纹同时存在，在镜面形成花纹，或者其中有一两套波纹占优势。提出了脉冲激光辐照下光学元件损伤区边缘产生波纹的一种光干涉模型：认为样品表面本身存在微米级杂质颗粒或者表面缺陷点在激光辐照下首先产生鼓包变形，鼓包或杂质颗粒将激光反射（散射）在未发生变形的区域，与直接辐照在该区域的激光束产生干涉，使得变形区周围的光强呈周期性分布，当变形区进一步损伤后，则在损伤区周围留下了波纹状图案。模拟实验验证了这种设想。     

Thermooptical Mechanism of Sound Generation by High-Power Laser Radiation Propagating in the Atmosphere

In the present paper, the results of experimental and theoretical investigations into the thermooptical mechanism of sound generation by high-power pulsed laser radiation (HPLR) propagating in the atmosphere are given. Experiments were performed with collimated and weakly-focused beams of a pulsed CO₂ laser with a wavelength of 10.6 m. A sound pulse was recorded with omnidirectional microphones placed at distances of 0.2–0.5 m from the laser beam axis and spaced along the laser beam propagation path whose length was a few hundred meters. A sound pressure level was measured with a precision impulse sound level meter, and time histories of acoustic pulses were also displayed on the screen of an oscilloscope. Based on these investigations, the methods of thermoacoustic sounding of the effective HPLR beam radius and divergence angle, the laser energy absorption coefficient, and the total laser energy have been suggested and realized together with the method of the diagnostics of HPLR propagation regime from the waveform or spectrum of the received acoustic signal.