复合脉冲激光辐照下三结GaAs电池的损伤特性

根据傅里叶热传导理论和热应力场理论,利用COMSOL仿真软件和Matlab软件构建了复合激光辐照下三结GaAs太阳能电池的复合损伤模型,计算了单毫秒激光和复合脉冲激光辐照下太阳能电池的温度和应力场分布。结果表明,相比单毫秒激光,复合激光辐照会产生更大范围的熔化损伤并且伴随出现明显的应力损伤,损伤面积和深度会随着纳秒脉冲激光能量密度和作用时间延时的增加而增加。能量密度增加到0.5 J/cm~2时,熔化损伤半径增大到2 mm,深度增大到1.5μm;时间延时增加到0.5 ms时,熔化损伤半径增大到1.4 mm,深度增大到1μm。     

激光损伤He—Ne散射探测法研究

介绍了He-Ne散射检测激光损伤的原理和实验装置，分析了散射信号及激光损伤的内在关系。实验表明，散射信号与薄膜的激光损伤尺度与形貌有关，对于本次实验，最小探测的激光损伤尺度为20μm左右。与显微镜和等离子体闪光法实验对比显示，He-Ne散射测量能判定薄膜激光损伤的发生，准确测量激光损伤闽值，测量结果与显微镜观察法符合较好。     

熔石英光学材料紫外皮秒激光损伤的瞬态特性研究

光学元件激光损伤是限制高功率激光装置输出能力的关键因素,为了理解光学元件激光损伤过程,提高光学元件抗激光损伤性能,利用偏振阴影显微镜成像技术和光电探测技术研究了紫外皮秒激光诱使熔石英光学元件损伤的时间分辨动力学过程。结果显示了紫外皮秒激光作用过程中冲击应力波的传输特性、瞬态吸收的演变过程以及裂缝的发展过程。结果表明,冲击应力波的传输速度约为6.9μm/ns;532nm波长的激光瞬态吸收在激光作用之后2.5μs时激光吸收达到最大值,之后缓慢下降,整个持续时间可达50μs以上;损伤裂纹在7.5ns时刻就基本停止增长。研究结果对理解皮秒激光的损伤机制有重要意义。     

中红外2μm KTA光参量振荡器的输入镜膜层损伤分析

对基于KTA(KTiOAsO4,砷酸钛氧钾)晶体的中红外2μm光参量振荡器的输入镜膜层损伤现象进行了初步分析及对比实验研究,表明薄膜缺陷导致的热效应是造成输入镜膜层损伤、抗损伤阈值低的主要原因,同时发现由于腔镜失调等原因造成的腔内残余1.06μm激光是造成膜层损伤的主要来源,这些结果对改进光参量振荡器系统设计、进一步提高2μm激光输出能量具有一定的指导作用。     

Q开关Nd:YAG脉冲激光对红外滤光片的损伤效应

 介绍了由滤光片膜层结构决定的激光在光学薄膜中形成温度场及驻波场特性。用1.06μm调Q Nd:YAG激光器，在激光脉冲宽度10ns和光斑直径0.61μm的条件下，进行了激光辐照红外滤光片的损伤特性实验研究。根据脉冲激光辐照红外滤光片后样品损伤分析，发现滤光片的最初损伤发生在里面的膜层中，从而在实验上验证了计算得到的滤光片膜层中存在其温度场及驻波场的结果。它对提高红外滤光片的抗激光辐照能力研究具有一定的参考价值。     

不同膜系结构的光学薄膜的激光损伤研究

本文报道了偏振膜和1.06μm高反膜的激光损伤。研究了膜系结构与损伤阈值的关系,并对实验结果作了分析。     

激光作用下环氧/硅树脂复合涂层的1.3μm反射特性研究

利用共轭反射计装置,开展了真空环境中激光作用下环氧/硅树脂双层结构复合涂层的1.3μm反射特性研究,测量得到了涂层反射率随样品背表面温度的变化曲线。通过有限元分析和界面热阻修正得到了反射率随涂层温度的变化关系,探讨了反射率随温度的变化机理。研究结果表明,红外连续激光损伤环氧/硅树脂复合涂层,主要表现为底漆热解引发的鼓包分层和面漆热解导致的烧蚀变色;常温下涂层对1.3μm激光的反射率约为0.80,激光辐照初始时变化不明显,鼓包前后出现波动,测量区涂层鼓包、烧蚀后反射率显著下降,最终保持在一个相对较低值;反射率变化与涂层热解过程、损伤方式密切相关,涂层对1.3μm激光的反射率变化存在3个特征温度,分别对应底漆热解、面漆热解和表面状态趋于稳定时的温度。     

大口径氘化磷酸二氢钾晶体离线亚纳秒激光预处理技术

大口径氘化磷酸二氢钾(DKDP)晶体抗激光损伤性能偏低严重地制约着大型高功率激光装置输出水平.本研究利用离线亚纳秒激光预处理技术有效地提升了大口径DKDP晶体抗激光损伤性能.实际使用情况表明,采用离线亚纳秒激光预处理后,DKDP晶体在9 J/cm²激光通量辐照下的表面平均损伤密度得到大幅下降,由未处理前的5.02 pp/cm²(1pp表示1个百分点)降至0.55 pp/cm²,降幅为一个数量级.同时,激光预处理对晶体损伤尺寸具有一定的抑制作用,预处理后晶体损伤点尺寸分布曲线向尺寸减小的方向平移,尺寸分布峰值由预处理前的25μm降至预处理后的18—20μm.     

锶蒸气中原子激光与离子激光的同时振荡

通过锶蒸气中的高频脉冲放电,实现了锶原子6.45μm自终止跃迁激光和锶离子1.03μm/1.09μm自终止跃迁激光的同时振荡.其中6.45μm激光最大激光平均功率为273mW.在对比实验的基础上分析和讨论了主要工作参数对这两组激光输出影响的差异.     

用透射反射扫描法检测光学薄膜的激光损伤

 用波长1.06μm的激光透射反射自动扫描装置扫描了激光辐照前后薄膜的反射比和透射比。薄膜样品的工作波长为1.06μm。将扫描结果与相衬显微镜观察到的形貌相对照。实验结果表明，用透射反射扫描法不仅能反映出相衬显微镜所能观察到的损伤，而且也能发现某些显微镜所不能发现的损伤。由于透射比和反射比可以反映出薄膜对激光的传输性能，因此也能反映出薄膜能否继续工作，以此来判定损伤与否。因此用透射反射扫描法可以作为检测损伤的手段，由于简单易行，可以在线检测。避免目前损伤测试工作中繁重的人工操作。     

Pulsed laser damage of proustite

Pulsed laser damage thresholds have been measured for proustite (Ag₃ As S₃) as the wavelengths 0.694, 1.065, 1.32 and 10.6 μm. The damage thresholds have been found to vary with both the wavelength and duration of the irradiating pulse. At 1.065 μm damage thresholds are 0.38 J/cm² for pulses of duration <50 ns whilst for durations >50 ns a value of 7 MW/cm² is appropriate. The results suggest that damage is initiated by absorbing inclusions approximately 0.6 μm in diameter embedded within the crystals. These inclusions are heated by an incident pulse to cause catastrophic damage of both the surface and interior of an irradiated sample. A model has been developed to enable a study of the thermal behaviour of inclusions irradiated by laser pulses with Gaussian time-dependence to be made.     

脉宽对中红外激光带内损伤HgCdTe材料的影响

研究了脉宽对于中红外脉冲激光带内损伤碲镉汞（HgCdTe）材料阈值的影响,使用一维自洽模型对激光辐照HgCdTe材料程中的载流子数密度,载流子对数目流,载流子对能流,载流子温度和材料晶格温度等相关参数进行仿真计算。仿真结果表明,波长2.85 μm,脉宽30 ps～10 ns单脉冲激光带内辐照HgCdTe材料的损伤阈值为200～500 mJ/cm2。其中,300 ps～3 ns脉冲激光的损伤阈值相近,均为200 mJ/cm2且低于其他脉宽激光的损伤阈值。搭建实验光路并进行相关实验验证仿真模型的正确性。实验发现,波长2.85 μm、脉宽300 ps的单脉冲激光带内辐照HgCdTe材料的损伤阈值在200 mJ/cm2左右。相同条件下,10 ns单脉冲激光带内辐照HgCdTe材料的损伤阈值约474 mJ/cm2。百皮秒脉冲激光对HgCdTe材料的损伤过程结合了热击穿和光学击穿效应,其独特的毁伤机理加剧了材料的损伤。     

Plasma-mediated ablation of brain tissue with picosecond laser pulses

Plasma-mediated ablations of brain tissue have been performed using picosecond laser pulses obtained from a Nd:YLF oscillator/regenerative amplifier system. The laser pulses had a pulse duration of 35 ps at a wavelength of 1.053 µm. The pulse energy varied from 90 µJ to 550 µJ at a repetition rate of 400 Hz. The energy density at the ablation threshold was measured to be 20 J/cm². Comparisons have been made to 19 ps laser pulses at 1.68 µm and 2.92 µm from an OPG/OPA system and to microsecond pulse trains at 2.94 µm from a free running Er:YAG laser. Light microscopy and scanning electron microscopy were performed to judge the depth and the quality of the ablated cavities. No thermal damage was induced by either of the picosecond laser systems. The Er:YAG laser, on the other hand, showed 20 µm wide lateral damage zones due to the longer pulse durations and the higher pulse energies.     

Intense laser flux effects on GaAs

Surface damage measurements on GaAs for pulsed laser flux at 0.694 μm, 1.06 μm, and 10.6 μm are presented. The damage threshold is seen to increase with the flux wavelength and decrease with increasing pulse duration. Other experiments were performed which indicated that the initial effect of the laser beam is to produce expansion of the bulk material and that the interband Faraday rotation at 1.06 μm is not dependent on laser intensity.     

Mitigation of laser damage growth in fused silica by using a non-evaporative technique

A non-evaporative technique is used to mitigate damage sites with lateral sizes in a range from 50 μm to 400 μm and depths smaller than 100 μm.The influence of the pulse frequency of a CO 2 laser on the mitigation effect is studied.It is found that a more symmetrical and smooth mitigation crater can be obtained by increasing the laser pulse frequency form 0.1 to 20 kHz.Furthermore,the sizes of laser-affected and distorted zones decrease with the increase of the laser pulse frequency,leading to less degradation of the wave-front quality of the conditioned sample.The energy density of the CO 2 laser beam is introduced for selecting the mitigation parameters.The damage sites can be successfully mitigated by increasing the energy density in a ramped way.Finally,the laser-induced damage threshold(LIDT) of the mitigated site is tested using 355 nm laser beam with a small spot(0.23 mm 2) and a large spot(3.14 mm 2),separately.It is shown that the non-evaporative mitigation technique is a successful method to stop damage re-initiation since the average LIDTs of mitigated sites tested with small or large laser spots are higher than that of pristine material.     

长脉冲激光对组成CCD图像传感器的MOS光敏单元的硬破坏机理研究

以帧转移型面阵CCD图像传感器为例,采用有限元法研究了波长1.06 μm,脉宽ms量级长脉冲Nd:YAG激光与组成CCD传感器的MOS光敏单元的作用过程及硬破坏机理.建立了长脉冲激光辐照MOS光敏单元的热力耦合模型,模拟了MOS光敏单元的温度分布和应力分布.研究结果表明:在长脉冲激光作用下,由于S层表面径向压应力超过其抗压强度引起MOS光敏单元出现了OS层间分裂,进而受径向、环向和轴向压应力的共同作用下,在光敏单元还未熔融时,层间分裂就扩大至光敏单元的整个OS层间.OS层间完全分裂会使光敏单元发生硬破坏,并造成CCD传感器中激光照射区的单个或一列光敏单元的功能完全失效.文章的研究结果可为CCD图像传感器的激光损伤及防护提供必要的理论依据. 关键词： 长脉冲激光 CCD图像传感器 硬破坏机理 层间分裂     

激光对半导体材料损伤的机理研究

研究了半导体材料对激光的吸收机制。运用一维热传导方程以及载流子耦合扩散方程研究了激光与半导体材料相互作用的热输运、自由载流子输运过程。分析了半导体材料的热学损伤、力学损伤,以及光电探测器的击穿损伤机制。应用数值模拟的方法对Nd:YAG脉冲激光(1.06μm)辐照下感兴趣的半导体材料PbS内部瞬时温度场分布进行了模拟。     

Directly diode-pumped high-energy Ho:YAG oscillator

We report on the high-energy laser operation of an Ho:YAG oscillator resonantly pumped by a GaSb-based laser diode stack at 1.9 μm. The output energy was extracted from a compact plano-concave acousto-optically Q-switched resonator optimized for low repetition rates. Operating at 100 Hz, pulse energies exceeding 30 mJ at a wavelength of 2.09 μm were obtained. The corresponding pulse duration at the highest pump power was 100 ns, leading to a maximum peak power above 300 kW. Different pulse repetition rates and output coupling transmissions of the Ho:YAG resonator were studied. In addition, intracavity laser-induced damage threshold measurements are discussed.     

Surface damage morphology investigations of silicon under millisecond laser irradiation

The surface damage morphologies of single crystal silicon induced by 1064 nm millisecond Nd:YAG laser are investigated. After irradiation, the damage morphologies of silicon are inspected by optical microscope (OM) and atomic force microscope (AFM). The plasma emission spectra of the damaged region are detected by the spectrometer. It is shown that surface oxidation and nitridation have occurred during the interaction of millisecond laser with silicon. In addition, the damage morphologies induced by 2 ms and 10 ns pulse width laser are compared. The damage morphology obtained by 2 ms laser is an evident crater. Three types of damage morphologies are formed at different laser energy densities. The circular concentric ripples are found surrounding the rim of the crater. The spacing of the ripples is 15 ± 5 μm. Two types of cracks are observed: linear crack and circular crack. The linear crack is observed in the center of the damaged region which propagates to the periphery of the damaged region. The circular crack is located at the rim of the crater. The damage morphology induced by 10 ns laser is surface layer damage. The periodic linear waves are generated due to the interference between the incident beam and the scattered beam. The spacing of the ripples is 1.54 μm which is close to the incident laser wavelength 1.064 μm. The linear crack is located at the center of the damaged region. Furthermore, for the same laser energy density, the dimension of the damaged region and the crater depth induced by 2 ms laser are greater than that of 10 ns laser. It indicates that the damage mechanism under millisecond pulse laser irradiation is strongly different from the case of nanosecond pulse laser.     

1.06μm连续与脉冲激光对GaAs材料的联合破坏效应

 通过1.06μm连续激光和脉冲激光联合破坏GaAs材料的实验研究, 给出了GaAs材料在三种不同的连续激光功率密度辐照下, 所需脉冲激光的破坏阈值, 结果表明, 联合破坏时所需脉冲激光的破坏阈值小于单独使用脉冲激光的破坏阈值。根据轴对称二维热模型, 计算了三种情况下连续激光辐照时GaAs材料的表面温度分布曲线及表面辐照中心处温升随辐照时间的关系, 并估算了其后作用的脉冲激光对材料的温升, 对实验及计算结果进行了分析, 并着重比较了联合破坏方式和单独破坏方式的优缺点。