Study on the beam shaping of high-power laser diode bars

Based on the Collins form, the intensity distribution of the resulting beam is derived when Gaussian beams of a high-power laser diode bar pass through a paraxial optical system. Then flattop beam profiles are obtained by a concave cylindrical lens, and the propagation properties are discussed in detail, such as the peak-intensity axis inclined at an angle γi. In addition, an expression to calculate beam angular width is presented.     

对晶体光损伤阈值测量的一种新方法的研究

提出一种测量晶体光损伤阈值的新方法,即确定激光横向功率密度的空间分布,利用晶体的激光损伤斑点半径,直接计算出晶体光损伤阈值,并给出入射激光为高斯光束时晶体损伤阈值与其损斑半径的关系。以提拉法生长的掺镁铌酸锂(MgO：LiNbO3)晶体为研究对象,用该方法测量其损伤阈值,得到了定量结果且所得数据与文献已报道的规律相符。分析得出同样激光条件下．损斑半径越大的晶体其光损伤阈值越小的结论,指出该方法同样适用于其他晶体或非高斯光束条件下光损伤阈值的测量并对具体作法进行了讨论。该测量方法弥补了常用测量方法只能定性或半定量的不足,可用于晶体抗光损伤阈值的精确测量。     

光学薄膜抗激光损伤研究发展

随着大能量/高功率激光器的发展需求日益突出,光学薄膜的激光损伤阈值逐步成为激光器发展的瓶颈,受到国内外高能激光器研究领域的广泛关注。阐述了光学薄膜激光的损伤机理、激光损伤阈值测试平台及方法,结合自身研究成果,综述性分析了国内外光学薄膜抗激光损伤技术与手段研究的发展情况,主要包括离子束预处理、离子束与退火后处理、虚设保护层等;重点提出了磁过滤结合激光沉积的复合沉积技术,并建议加速推动无缺陷沉积的原子层沉积技术,为大幅提高光学薄膜抗激光损伤能力、满足当前需求提供了理论基础。     

激光光热偏转成象法无损检测光学薄膜的激光损伤

介绍了应用激光光热偏转成象法无损检测光学薄膜激光损伤的基本原理，由此建立了实验检测装置，对光学薄膜表面的激光损伤进行了扫描检测，并以直观的灰度象显示. 实验结果证明了激光光热偏转成象法检测光学薄膜激光损伤具有直观、有效、可确定损伤阈值的优点.     

离子束技术对氧化铪薄膜性能的影响

 在基底清洗、薄膜沉积和薄膜后处理三个阶段均采用离子束技术,制备了氧化铪薄膜,并对薄膜的光学性能、表面特性和激光损伤阈值特性进行测试和研究。结果表明,利用离子束技术清洗基底可以增强表面吸附;离子束辅助沉积在合适离子束能量下可以得到高堆积密度、高损伤阈值的薄膜;离子束后处理氧化铪薄膜可以降低表面粗糙度,改善抗激光损伤阈值。说明在三个薄膜制备阶段同时采用合适的离子束参数可以制备出结构致密、阈值高、表面粗糙度好的氧化铪薄膜。     

Flattop beam illumination for 3D imaging ladar with simple optical devices in the wide distance range

We have developed an illumination optical system for 3D imaging ladar (laser detection and ranging) which forms flattop beam shape by transformation of the Gaussian beam in the wide distance range. The illumination is achieved by beam division and recombination using a prism and a negative powered lens. The optimum condition of the transformation by the optical system is derived. It is confirmed that the flattop distribution can be formed in the wide range of the propagation distance from 1 to 1000 m. The experimental result with the prototype is in good agreement with the calculation result.     

离子束流后处理对类金刚石薄膜激光损伤特性的影响

类金刚石薄膜激光损伤阈值低,已经严重制约其在红外激光系统中的应用。基于非平衡磁控溅射技术,在硅基底上沉积类金刚石薄膜;采用离子束流后处理技术,用正交实验法确定影响处理效果的主要因素,对已沉积完成的DLC薄膜进行离子束轰击;在不同处理工艺下,观测薄膜样品的光学常数及拉曼光谱,最后进行了激光损伤测试。从测试结果可知,离子束流后处理参数:离子能量1000eV、放电电流30~40mA、轰击时间8min时,透射率由原来的60.65%提高到了65.98%;消光系数在900nm后明显降低,DLC薄膜的激光损伤阈值从0.69J/cm2提高到1.01J/cm2。     

He-Ne散射光检测光学薄膜激光损伤阈值

准确测定光学薄膜的激光损伤阈值可以衡量光学薄膜的抗激光损伤能力,测定损伤阈值的关键是准确地判定损伤的发生与否。建立了He-Ne散射光检测光学薄膜激光损伤阈值系统。通过测量同一样品点的He-Ne散射光能量变化来判断薄膜表面发生的损伤,并对制备的类金刚石薄膜与HfO₂/SiO₂反射膜进行了阈值测试。与等离子体闪光法的阈值测试结果进行比较,具有较好的一致性。分析表明：He-Ne散射光测试系统能有效地判断出激光诱导损伤,易于实现在线检测。     

Kinetics of Anisotropic Scattering and Optical Turbulence upon Laser Irradiation of AgCl:Ag Films

The kinetics of anisotropic scattering and optical turbulence upon formation of quasi-periodic structures (QPSs) in photosensitive composite AgCl:Ag films irradiated by Gaussian beams of a He-Ne laser is studied. The buildup kinetics of the scattering induced by an unfocused beam is used to find the threshold exposures for the formation of QPSs and an additional spatiotemporal instability resulting from interaction between the gratings during their development. It was established that there exists a threshold for the formation of a strong instability (optical turbulence) when the QPSs are induced by a focused beam. The decay curves of the mean frequency of the chaotic intensity oscillations, as well as the dependence of this frequency on the beam power, are obtained under conditions of turbulence. It is shown that both the turbulence and its decay are controlled by a competition between the microgratings in the QPSs and by gradual widening of the area of active competition under the action of the Gaussian beam. The AgCl:Ag films are shown to be capable of rapidly and repeatedly rearranging the QPSs and the spatial orientation of the anisotropic scattering upon variation of the direction of linear polarization of the laser beam.     

Damage performance of TiO2/SiO2 thin film components induced by a long-pulsed laser

In order to study the long-pulsed laser induced damage performance of optical thin films, damage experiments of TiO₂/SiO₂ films irradiated by a laser with 1 ms pulse duration and 1064 nm wavelength are performed. In the experiments, the damage threshold of the thin films is measured. The damages are observed to occur in isolated spots, which enlighten the inducement of the defects and impurities originated in the films. The threshold goes down when the laser spot size decreases. But there exists a minimum threshold, which cannot be further reduced by decreasing the laser spot size. Optical microscopy reveals a cone-shaped cavity in the film substrate. Changes of the damaged sizes in film components with laser fluence are also investigated. The results show that the damage efficiency increases with the laser fluence before the shielding effects start to act.     

45°高反膜中节瘤缺陷的电场增强效应及损伤特性

研究设计和制备了中心波长为1064 nm的45°多层膜反射镜,通过数值仿真结合实验,对薄膜中节瘤缺陷引起的电场增强效应及其对薄膜抗激光损伤性能的影响进行了研究。结果表明:当1064 nm激光从右至左45°斜入射时,电场增强效应主要出现在节瘤缺陷的表层及其左侧轮廓中部,电场增强效应随节瘤缺陷尺寸增大而增强。实验上,在清洁的基板表面喷布单分散SiO2微球作为人工节瘤种子,采用电子束蒸发制备法完成多层全反膜的制备,采用R-on-1方式对薄膜样品进行激光损伤测试。结果表明,薄膜的损伤阈值随着节瘤缺陷尺寸增加而减小。通过综合分析电场增强效应、薄膜损伤测试结果及损伤形貌特征得出,薄膜损伤阈值降低是由于节瘤缺陷和薄膜中微缺陷共同作用的结果。     

激光薄膜损伤的声频判别方法

光学薄膜损伤阈值是衡量光学薄膜抗激光损伤能力的重要参数,而要实现损伤阈值的测试必须先实现薄膜损伤的判识。利用光声频谱特性研究单层氧化硅薄膜在不同激光能量下的损伤情况,简要地分析了声频法判别薄膜损伤的可行性,建立了激光致薄膜产生的声波采集系统,比较和分析薄膜损伤前后的24~40kHz高频段曲线,提取频率特征,并提出利用曲线相似函数进行薄膜损伤的识别。实验数据结果表明,该方法简单易行,可实现在线检测,又能准确判别薄膜损伤。     

1 064 nm与532 nm激光对电子束蒸发制备的HfO2/SiO2高反膜损伤比较

 研究了电子束蒸发制备的HfO₂/SiO₂高反膜在1 064 nm与532 nm激光辐照下的损伤行为。基频激光辐照时损伤形貌主要为节瘤缺陷喷溅留下的锥形坑,当能量密度较大时出现分层剥落;二倍频激光损伤主要是由电子缺陷引起的平底坑,辐照脉冲能量密度稍高时也会产生吸收性缺陷引起的锥形坑,但电子缺陷的损伤阈值更低;随着辐照脉冲能量密度的增大分层剥落逐渐成为主要的损伤形貌。分析认为,辐照激光波长的变化,引起吸收机制的变化从而导致了损伤阈值及损伤机制的差异。     

A New theory for evaluating the number density of inclusions in films

A new formulation derived from thermal characters of inclusions and host films for estimating laser induced damage threshold has been deduced. This formulation is applicable for dielectric films when they are irradiated by laser beam with pulse width longer than tens picoseconds. This formulation can interpret the relationship between pulse-width and damage threshold energy density of laser pulse obtained experimentally. Using this formulation, we can analyze which kind of inclusion is the most harmful inclusion. Combining it with fractal distribution of inclusions, we have obtained an equation which describes relationship between number density of inclusions and damage probability. Using this equation, according to damage probability and corresponding laser energy density, we can evaluate the number density and distribution in size dimension of the most harmful inclusions.     

An Iteratively-Designed Binary Phase Grating for Flattop Beam Generation

A binary phase grating capable of shaping an incident Gaussian beam to a flattop beam in a Fourier domain is designed iteratively. It is essential in grating design to consider the phases of diffracted waves by the grating, in addition to their amplitude uniformity and diffraction efficiency. The optimized grating phase produces the in-phase diffracted waves that interfere constructively to form a uniform amplitude and phase profile. The dependence of the shaped profile on the illuminating amplitude distribution, the grating misalignment, and the lens focusing error is investigated by computer simulation and optical experiment.     

1 064 nm激光对氧化铟锡薄膜的损伤研究

 液晶光学器件在激光光束精密控制上具有重要应用前景,氧化铟锡（ITO）薄膜作为液晶光学器件的透明导电电极,是液晶器件激光损伤的薄弱环节。为此,建立了ITO薄膜激光热损伤物理模型。理论计算结果表明：1 064 nm激光对ITO薄膜的损伤主要为热应力损伤;连续激光辐照下,薄膜损伤始于靠近界面的玻璃基底内;脉冲激光辐照下,温升主要发生在光斑范围内的膜层,薄膜损伤从表面开始。利用泵浦探测技术,研究了ITO薄膜的损伤情况,测量了不同功率密度激光辐照后薄膜的方块电阻,结合1-on-1法测定了ITO薄膜的50%损伤几率阈值。实验结果表明：薄膜越厚,方块电阻越小,激光损伤阈值越低;薄膜未完全损伤前,方块电阻随激光功率密度的增加而增大。理论计算与实验结果吻合较好。设计液晶光学器件中的ITO薄膜电极厚度时,应综合考虑激光损伤、透光率及薄膜电阻的影响。     

A novel optical diagnostic technique for analyzing the recrystallization characteristics of polycrystalline silicon thin films following frontside and backside excimer laser irradiation

Excimer laser annealing (ELA) is a widely used technique for producing polycrystalline silicon (poly-Si) thin films. An optical inspection system with simple optical arrangements for rapid measurement of recrystallization results of poly-Si thin films is developed in this study. The recrystallization results after both frontside ELA and backside ELA can be easily visible from the profile of peak power density distribution using the optical inspection system developed with an optimized moving velocity of 0.312 mm/s of the specimen. The method of backside ELA is suggested for batch production of low-temperature polycrystalline silicon thin-film transistors due to higher laser beam utilization efficiency and lower surface roughness of poly-Si films.     

光纤激光器光学膜设计与制备

针对激光在传输过程中的光能损失,本文根据光学薄膜理论,设计制备了减反射膜和抗激光的高反射膜,并对激光膜的镀膜材料、膜系设计、沉积工艺及离子辅助沉积等参数进行了深入研究.研究结果表明,制备的减反膜的反射率＜O.2%,激光以25°～65°入射时高反射膜的反射率＞99.7%.对50μm光纤和K9玻璃镀膜前后的输出功率测试显示...     

HfO2薄膜的结构对抗激光损伤阈值的影响

利用蒸发氧化铪和离子辅助蒸发金属铪反应沉积氧化铪薄膜，对两种工艺下制备的氧化铪薄膜进行光学和结构以及激光损伤特性的研究. 实验结果表明，用金属铪反应沉积的氧化铪薄膜不仅结构均匀，并且具有较高的激光损伤阈值. 文章对损伤阈值和薄膜的结构及光学特性之间的关系进行了讨论.     

氧分压对ZrO2薄膜激光损伤阈值的影响

 在不同的氧分压下用电子束热蒸发的方法制备了ZrO₂薄膜。分别通过X射线衍射、光学光谱、热透镜技术、抗激光辐照等测试，对所制备样品的微结构、折射率、吸收率及激光损伤阈值进行了测量。实验结果表明，薄膜中晶粒主要是四方相为主的多晶结构，并且随着氧分压的增加，结晶度、折射率以及弱吸收均逐渐降低。薄膜的激光损伤阈值开始随着氧分压增加从18.5J/cm²逐渐增加，氧分压为9×10^-3Pa时达到最大，值为26.7 J/cm²，氧分压再增加时则又降低到17.5 J/cm²。由此可见，氧分压引起的薄膜微结构变化是ZrO₂薄膜激光损伤阈值变化的主要原因。