窄带干涉滤光片抗击不同输出方式激光的损伤特性研究

利用Nd∶YAG调Q单脉冲激光和自由脉冲激光对硬膜窄带干涉滤光片进行激光损伤阈值的测试，并且采用表面热透镜技术测量了滤光片的吸收率。实验发现:窄带干涉滤光片的吸收率和激光损伤阈值强烈依赖于辐照激光波长与窄带干涉滤光片通带的相对位置；在调Q单脉冲激光作用下，不同中心波长的滤光片损伤形貌存在明显的差别，而在自由脉冲激光作用下，各滤光片的损伤形貌则趋于相同，均表现为典型的热熔烧蚀破坏。根据实验结果，结合损伤形貌，通过驻波场理论对激光作用下滤光片内电场分布的分析与模拟，探讨了两种激光模式作用下滤光片的损伤特征和损伤机理的不同特点。     

光学元件激光预处理技术

国外学者用1064 nm激光对pickoff镜进行预处理,发现损伤阈值平均提高38.8%。国内研究者用CO2激光中度抛光后,熔石英基片的损伤阈值提到了30%左右,激光波长、扫描方式等对处理效果影响也比较明显。介绍了三种公认的预处理机制,将离线与在线处理方式做了简单地比较,并对国内外激光预处理技术的发展和前景进行了展望。     

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。     

Electron beam evaporated LaF3 thin films prepared by different temperatures and deposition rates

LaF₃ thin films were prepared by electron beam evaporation with different temperatures and deposition rates. Microstructure properties including crystalline structure and surface roughness were investigated by X-ray diffraction (XRD) and optical profilograph. X-ray photoelectron spectroscopy (XPS) was employed to study the chemical composition of the films. Optical properties (transmittance and refractive index) and laser induce damage threshold (LIDT) at 355 nm of the films were also characterized. The effects of deposition rate and substrate temperature on microstructure, optical properties and LIDT of LaF₃ thin films were discussed, respectively.     

Effect of porosity on the laser induced damage threshold of porous anodic alumina films

Thermal stress of porous alumina films has been simulated by finite element method based on thermal transfer equation and thermal stress formulas. The influence of equivalent thermal conductivity and elastic modulus on laser induced damage threshold (LIDT) has been studied. It was found that the biggest circumferential tensile stress will be small with the porosity from 15% to 35%, and it effectively improves the LIDT. The equivalent thermal conductivity and LIDT decreases with the increase of porosity. The equivalent elastic modulus decreases and LIDT increase with the increase of porosity.     

Laser Induced Damage in CVD Diamond Films

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Study on Laser Conditioning of Optical Coatings

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疏水性对溶胶-凝胶SiO2薄膜抗真空污染及抗激光损伤能力的影响

以正硅酸乙酯作为前驱体, 利用碱催化方式制备了SiO₂溶胶, 通过在溶胶中添加含疏水基团(-CH₃)的六甲基二硅氮烷(HMDS)对溶胶进行改性, 使用添加不同物质的量比HMDS改性后的溶胶用提拉法在K9基片上镀膜, 获得了具有疏水性能的SiO₂薄膜。采用自制接触角测量仪、紫外-可见-近红外分光光度计研究了薄膜的水接触角和透过率。测试了薄膜的激光损伤阈值, 并观察了激光辐照后薄膜的损伤形貌。通过真空污染实验对薄膜的抗污染能力及抗激光损伤能力进行了研究。实验结果表明:经疏水改性的溶胶所镀制的薄膜激光损伤阈值由未改性样品的24.3 J·cm^-2增加到37 J·cm^-2(1 064 nm, 10 ns), 且抗真空污染能力大大加强:在真空环境下保存168 h后, 未改性样品的峰值透过率下降了2%, 而疏水改性后的样品峰值透过率仅下降了0.25%, 并保持了较高的激光损伤阈值(30.8 J·cm^-2)。     

Thermal and mechanical damage of GaAs in picosecond regime

An in-depth study of the single pulse and multiple pulse laser (35 ps, 10 Hz and 1064 nm) damage for threshold fluence and greater fluence of GaAs 1 0 0 single crystal is presented. Damage which starts at a power 2×10¹¹ W/cm² in the form of pits occurs due to accumulation of laser induced microscopic defects. Effect of multiple pulse at first makes the pits more prominent in the form of Ga emission. Then the topmost layer is removed. If the number of pulses is further increased new pits are formed in the new surface (beneath the removed surface) and the above process is repeated. The thermal model is sufficient to explain this morphology. However, for larger fluences, a large cracking and fracture and the possibility of both Ga and As emission in different ratios suggest that mechanical damage is a dominant feature for higher fluences which arises due to generation of shock waves and rapid vaporization of material. Damage threshold has been calculated with the help of the thermal model given by Meyer et al. which is in good agreement with our experimental results.     

力学边界对透射型光学元件激光破坏阈值的影响

 建立了激光与透射型光学元件相互作用的热弹性力学模型,解析求解了自由、固定以及一种人为边界条件下光学元件热-力学响应的定解问题。研究发现,不同的边界条件对破坏阈值有很大的影响。针对光学元件中热应力的演变情形,设计了一种“最佳”边界,消除了激光作用过程中产生的拉应力,从而使破坏阈值在理论上达到最大值。