Fabricating of aspheric micro-lens array by excimer laser micromachining

This work presents a unique method for fabricating aspheric micro-lens array based on a KrF 248 nm excimer laser micromachining with precise surface profile control. Based on a planetary contour scanning laser machining method along with a shading metal mask and sample movable stage, an array of micro-lenses with precisely controlled surface profiles can be fabricated. Each lens surface profile can be aspheric and pre-designed. Experiments have been carried out and the machining accuracy of each lens surface profile is examined. Good surface roughness and profile accuracy are observed.     

Enhancement of Optical Fiber Coupling Based on Collimated and Focused Laser Diode Beam with Micro Aspherical Plano-Convex Lens Fabricated by Excimer Laser

In this article, we have proposed and demonstrated experimentally the double plano-convex micro-aspherical lens scheme to amplify an edge-emitting laser diode (LD) to optical fiber coupler. Both microlenses have two different profiles along their x- and the y-axes direction. The optical simulation software Zemax is used to design and optimize the proposed microlens profile and then fabricate by an excimer laser micromachining system. Focal spot size of LD around 9 µm is achieved experimentally. Light coupling efficiency between LD and optical fiber, using this double plano-convex microlens, is 27.57% and 44.23% for single-mode and multi-mode fiber, respectively.     

平凸型氮化硅球面微透镜的研究

介绍了用激光化学汽相沉积球面微透镜的技术，首先对激光化学汽相沉积法获得球面微透镜进行了理论分析，并用计算机分析了在一定沉积技术下的微透镜厚度剖面形状及光学聚集特性。其后介绍了激光化学汽相沉积的实验装置，用该装置在平面石英玻璃衬底上，制出了平凸型氮化硅球面微透镜，并对其参量进行了测量。     

Discussions on on-machine measurement of aspheric lens-mold surface

At present, regarding to the machining of aspheric lens mold, there are two major methods to carry out the on-machine measurement (OMM) — contacting method (CM) and non-contacting method (NCM). Here such two methods are reviewed in detail. CM is mainly based on the contacting probe which is scratching aspheric surface of lens mold to achieve profile data. To be efficient, an idea with 45° tilt of probe is proposed for OMM of lens mold by Suzuki. But generally speaking, the contacting OMM is not so efficient and can only deal with axisymmetric aspheric lens mold. On the contrary, NCM mostly uses laser to achieve aspheric profile without any contact. On ultra-precision lathe, laser scanning system or laser interferometer is mounted on the frame of lathe and transfers measurement data to machining system efficiently. However, most NCMs need stable environment and low working noise except instantaneous phase-shifting shearing interferometry (IPSSI). Therefore, a new idea about IPSSI is proposed in this paper to realize OMM of lens molds. Unfortunately, it's also difficult to test the high numerical aperture aspheric or free-form lens molds. By comparison, the newly-developed fringe reflection (FR) method is becoming the promising method because it features the high efficiency and high accuracy. However, this method has not been used for OMM system yet. Much research should be conducted for FR OMM technology.     

电场作用下的变焦非球面液滴微透镜

提出了一种制作变焦非球面液滴微透镜并在线检测其光学性能的新方法。在实时进行光学检测的条件下,选择光固化材料,利用电场作用操控液滴透镜的面形实现变焦,在检测到较好的透镜面形和聚焦状态时,采用紫外光固化技术使液滴透镜固化,可制作具有良好光学成像和聚焦性能的非球面微透镜。研制了紫外光固化非球面液滴微透镜制作平台及在线检测系统,实验观察并讨论了液滴透镜面形和聚焦光斑随电场作用的变化规律,成功实现了液滴透镜的变焦,并获得了良好的非球面面形和聚焦光斑,证明了用此方法制作高成像性能的非球面微透镜的可行性。     

Direct writing and in-situ material processing by a laser-micromachining projection microscope

The new laser micromachining projection microscope enables a surface to be viewed at high magnification with a built-in facility for micromachining of the same surface according to a predetermined pattern. A XeCl-excimer laser forms part of the device and provides bright viewing illumination in amplified spontaneous emission as well as a small laser spot of sufficient fluence to mark the sample surface. The basic characteristics of image enhancement in the excimer amplifier are presented. The advantage of such a technique for both pattern generation, surface cleaning and mask correction is demonstrated on Al, Cu and W specimens with a spatial resolution better than 3 m.     

Analysis of KrF excimer laser beam modification resulting from ablation under closed thick film flowing filtered water

The application of a closed thick film flowing filtered water to immerse the ablation etching mechanism of an excimer laser poses interesting possibilities concerning debris control, modification of machined feature topography and modification of the ablation rate. Furthermore, these parameters have been shown to be dependent on flow velocity; hence, offering further user control of machining characteristics. However, the impact of this technique requires investigation. This contribution offers comparison of the calculated ablation pressure and the effect on feature surface characteristics given for laser ablation of bisphenol A polycarbonate using KrF excimer laser radiation in ambient air against laser ablation of the same substrate under closed thick film flowing filtered water immersion. Also, an impact of such immersion equipment on the optical performance of the micromachining centre used is quantified and reviewed. The pressure is calculated to have risen by a magnitude of 48, when using the liquid immersed ablation technique. This increase in pressure is proposed to have an increased surface roughness, promoting the number of asperities with a surface area lower than 16 μm²; resulting in a diffuse reflection of light and an apparent darkening of features. The focal length of the optical system was accurately predicted to increase by 2.958 mm, when using the closed flowing liquid immersion equipment. This equipment is predicted to have increased the optical depth of focus via reduction in the angle of convergence of the two defining image rays; yet the perceived focus, measured discretely by mean feature wall angle, was found to be 25% smaller when using the closed thick film flowing filtered water immersion technique instead of similar laser ablation in ambient air. A compressed plume interaction is proposed as a contributing factor in this change.     

Femtosecond pulsed laser ablation with spatial filtering

With the rise in demand for miniaturized features with better acute edge acuity and negligible thermal damage zone, one of the key vital areas lies in the refinement of the quality of the laser beam itself. Spatial filter is routinely used in optical micromachining systems to smoothen the Gaussian profile of the machining spot in order to obtain a feature of the desired quality. However, its profile smoothening effect has never been investigated for femtosecond pulsed laser micromachining process since the extremely high peak power of femtosecond pulses will cause damage on the filtering aperture of spatial filter. During the development of an acousto-optical micromachining system using femtosecond pulses, we found that if the damage of the filtering aperture can be circumvented, spatial filter can improve the machining quality of femtosecond pulse ablation, especially when ablation is conducted at low-fluency range (just above the ablation threshold fluency). In this paper, we investigate and demonstrate both the improvement and potential that beam refinement can bring about. In our experiment, a series of test patterns were ablated with a 400 nm second-harmonic Ti:Sapphire femtosecond laser of 150 fs duration at varying pulse energy ranging from 31 to 39 nJ. The specimen used in the experiment is a platinum- (Pt) sputtered coating of 100 nm thickness on a quartz substrate. The results show a significant improvement in the constancy of the shape as well as the size of ablated feature, revealing an improved beam profile and beam energy distribution due to spatial filtering.     

高分辨率长焦广角低畸变光学成像系统设计

鉴于全视角高精度三维测量仪中现有光学成像系统无法同时满足大视角、高分辨率和低畸变等技术指标,为此设计了一种能够同时克服上述缺陷的光学成像和畸变校正系统。采用复杂化双高斯结构形式进行f-θ镜头设计,引入非球面提高系统成像质量。实验结果表明,设计的光学系统为长焦广角低畸变高分辨率光学系统,在环境温度-10 ℃~70 ℃下,视场角达到90°,畸变小于-0.001 67%,传递函数达到0.4@100 lp/mm,可实现工作距离3 m~100 m成像清晰。同时,光学系统中非球面镜片的面型精度会对成像质量产生很大的影响,根据公差分析,非球面的面型精度PV值小于0.17 μm时系统成像质量满足要求,实际加工过程中非球面面型PV值达到0.158 μm,传递函数达到设计指标要求,提高了系统的成像质量。     

准分子激光的光束波面测量技术

 准分子激光在激光光刻和微细加工中有广泛的应用，要求激光具有好的稳定性和光束波面均匀性。介绍了准分子激光的波面特性以及波面分析测量技术。用波面分析仪对XeCl和ArF激光特性进行全面的测量和评估，给出了主要参数的测量结果，重点分析了光束均匀性。     

玻璃基底Wolter-1型X射线聚焦镜研制及测试

Wolter-1型X射线聚焦镜可将掠入射的X射线反射至焦平面处,具有较强的成像探测能力,在天文探测等领域中具有重要作用.通过建立几何模型对反射镜面及反射光线方程进行理论计算,推导出了适用于以玻璃为基底材料的聚焦镜设计参数方程,可用于对此类聚焦镜进行理论设计,依据理论设计,采用具有极高表面光洁度的超薄肖特D263T玻璃经热弯成型后作为反射镜基底,在反射镜表面制备金属铱薄膜作为反射膜研制了Wolter-1型反射镜组,并使用激光三维扫描仪对所研制的聚焦镜片面型进行了测试.测试结果显示,实际镜片面型与理想镜片面型公差在10 μm以内的测试点占总测试点的50%.通过搭建可见光条件下的焦斑测试系统,使用图像采集相机采集焦斑的灰度图像,通过图像分析软件分析计算该灰度图像的灰度分布来定量分析焦斑的能量分布情况,从而确定焦斑特性参数.实验结果显示：研制出的聚焦镜片焦距为1.6 m,焦斑的半能量包围直径为0.33 mm,对应角分辨率为0.7角分.     

亚波长衍射微透镜的设计

设计了连续浮雕衍射微透镜和与其等效的二元亚波长衍射微透镜,采用旋转体时域有限差分法对通过计算机辅助设计出的元件进行了严格的矢量分析,给出了各元件在焦平面的场强分布.分析结果表明,本文设计的二元亚波长微透镜对连续浮雕微透镜有很好的等效效果;填充因子的脉冲宽度调制法要优于填充因子的线性近似法;制作相对误差不大时深度误差和宽度误差对微透镜聚光能力的影响不大.     

Micro-lens arrays generated by UV laser irradiation of doped PMMA

Micro-lenses with well-defined optical parameters are generated on polymethylmethacrylate (PMMA) substrates doped with diphenyltriazene (DPT) by controlled use of a swelling effect generated under conditions of subablative excimer laser illumination. The surface profiles depend on the laser spot size and energy density. A sensitively balanced combination of matrix softening, substrate volume expansion due to photochemical nitrogen release, and surface tension is responsible for the final shape of the lenses. Complete arrays of identical lenses with 15 μm diameters and a focal length of 30 μm are produced by irradiation of (0.25 wt. %) DPT-PMMA with a single laser pulse at a wavelength of 308 nm and a fluence of 3 J/cm². It is shown experimentally and theoretically that appropriate volume expansion is possible without introducing internal light scattering due to the formation of small bubbles. Received: 7 April 1999 / Accepted: 8 April 1999 / Published online: 5 May 1999     

Mirau相移干涉法测量微透镜阵列面形

基于Mirau相移干涉法，在实验室环境下对微透镜阵列的微表面形貌进行了轮廓测量.实验使用He-Ne激光器作为光源，干涉成像系统由Mirau干涉物镜和其他光学元件组成.在实验中使用压电陶瓷执行器作为相移器，通过5步相移法计算待测表面形貌.实验结果表明，基于Mirau相移干涉法对微透镜阵列面形的测量，水平分辨率达到1.1 μm，垂直测量准确度达到6.33 nm，垂直测量范围为5 μm.对于微透镜阵列的面形测量，通过将微透镜阵列划分为若干微小区域以保证局部面形最大高度小于5 μm，然后辅以精密平移机构进行若干次5步相移法测量局部面形，再利用相位重建所得的数据进行拼接和3D轮廓重建，最终得到整个微透镜阵列的精确微表面形貌.     

基于Levenberg-Marquardt算法的大型非球面镜轮廓数据处理方法

大型非球面镜通过加工 检测 再加工 再检测的制造工艺以满足面形精度要求,根据检测后的轮廓数据准确评定面形是提高再加工精度的关键。为解决抛光前镜面的面形评定问题,采用基于信赖域法则的Levenberg Marquardt算法对参数进行拟合、误差补偿以及面形评定。利用Code V仿真分析算法性能,构建大型非球面轮廓仪测试抛物面加工件,对实测数据经过32次迭代得到元件参数及轮廓残差曲线,收敛精度为1.1610-21。实验表明:该算法可对大型非球面镜轮廓数据进行高效准确的拟合、评定,为进一步提高再加工精度提供可靠依据。     

应用离子束进行光学镜面确定性修形的实现

为了克服传统光学镜面抛光方法的缺点,提出了应用离子束进行光学镜面修形的方法.介绍了离子束修形技术的原理和方法,并对离子束修形中涉及的关键技术进行了讨论.在自研的离子束修形设备上对一块直径φ98 mm的微晶玻璃平面样件进行了离子束修形试验,经过两次的迭代修形使其面形精度均方根误差由初始的0.136λ提高到0.010λ(λ=632.8nm),平均每次迭代的面形收敛率达到3.7.实验结果表明,应用离子束进行光学镜面修形无边缘效应、面形收敛快、加工精度高;由于离子束修形技术去除材料过程自身的特点,使数控离子束修形技术对非球面的加工和对平面的加工难度相当.     

衍射极限非球面准直透镜

介绍了一种新的非球面透镜设计方法。通过非球面方程中二次曲面常数和非球面系数对光学系统像差的贡献来设计非球面透镜,并详细分析了非球面设计过程。设计了数值孔径NA=0.37, 纤芯Φ=600μm的大光束光纤耦合半导体激光器的非球面准直透镜,其焦距f=50mm。从像质评定可以看出, 非球面准直镜几乎接近衍射极限, 整个系统的波像差小于0.3λ。实验表明： 采用非球面准直系统能最大限度地利用光能率和提高光束准直性, 证明了设计方法基本正确。     

利用光斑图像特征确定飞秒激光有效烧蚀焦距

为确定飞秒激光光束对微尺度结构的烧蚀深度,研究了给定功率条件下对应的激光束有效烧蚀焦距。提出采用激光焦点处获得的烧痕阵列图像及在离焦状态下提取烧痕图像特征,通过分析图像特征与离焦距离,获得激光束有效烧蚀焦距范围的方法。在激光束焦点附近的硅晶片表面烧蚀出斑痕阵列,向下逐渐减小焦距,采集硅晶片斑痕图像,提取斑痕平均像素面积及斑痕目标与背景之间的R分量灰度差,获得斑痕像素面积及灰度差随激光束焦距变化的曲线;向上逐渐增大焦距,提取并获得斑痕像素面积及灰度差随激光束焦距变化的曲线。结合激光束向下离焦阈值(633 μm)及向上离焦阈值(993 μm),确定20 mW输出功率条件下,飞秒激光在硅晶片材料表面的有效烧蚀深度为360 μm。采用中位值方法确定了激光束在硅晶片表面聚焦时的焦距为0.823 mm。实验表明,激光烧蚀斑痕像素面积及灰度差与激光束焦距之间的关系能够客观地反映激光束有效烧蚀焦距的变化范围。     

An Investigation of Three-Dimensional Construction Methods in the Micromachining of Silicon Surfaces with an Ultraviolet Laser

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非球面碳化硅反射镜的加工与检测

为了获得高精度非球面碳化硅(SiC)反射镜,对非球面碳化硅反射镜基底以及改性后碳化硅反射镜表面的加工与检测技术进行了研究。介绍了非球面计算机控制光学表面成型（CCOS）技术及FSGJ-2非球面数控加工设备。采用轮廓检测法和零位补偿干涉检测法分别对碳化硅反射镜研磨和抛光阶段的面形精度进行了检测,并采用零位补偿干涉检测法及表面粗糙度测量仪对最终加工完毕的碳化硅反射镜的面形精度和表面粗糙度进行检测。测量结果表明：各项技术指标均满足设计要求,其中非球面碳化硅(SiC)反射镜实际使用口径内的面形精度（RMS值）为0.016λ(λ=0.6328μm）,表面粗糙度（RMS值）为0.85nm。