【作者】 单明广；

【导师】 谭久彬；

【作者基本信息】 哈尔滨工业大学 ， 光电信息与仪器工程， 2008， 博士

【摘要】 激光直写是制作衍射微结构光学元件的重要技术手段之一。随着微结构衍射光学大口径以及阵列化的需求发展,对激光直写写入效率和精度提出了更高的要求。传统激光直写技术采用单点曝光模式,无法实现较高的写入效率,而近年兴起的多点曝光并行激光直写,被认为最有潜力解决上述问题,但目前该技术存在写入分辨力和衍射效率不能兼顾、微透镜阵列聚焦模型不精确、写入光路和检焦光路分离而不能实时同步调焦写入等亟需解决的科学问题和关键技术问题,制约和影响了多点曝光并行激光直写技术的发展。本课题“用于并行激光直写的连续深浮雕谐衍射透镜阵列技术”研究的主要目的是解决多点曝光并行激光直写写入分辨力和衍射效率不能兼顾、微透镜阵列聚焦模型不精确、写入光路和检焦光路分离而不能实时同步调焦写入等问题,着重以连续深浮雕谐衍射透镜阵列为对象,开展理论描述、建模和实验研究工作,为高效、高分辨力多点曝光并行激光直写方法的研究提供理论依据和先期准备工作。该研究内容在光学传感、光通信、光计算、数据存储、激光医学以及多波段成像和聚焦系统等领域亦具有较高的应用价值。本课题研究的主要内容如下:为确定微透镜阵列对并行激光直写写入质量的影响规律,基于瑞利-索莫菲衍射理论,首先分析单微透镜非傍轴近似衍射聚焦特性,进而考虑相邻微透镜衍射聚焦的相互影响,建立了微透镜阵列非傍轴近似衍射聚焦模型,在此基础上分析了写入激光垂直入射时微透镜F/#以及中心距对微透镜阵列衍射聚焦的影响规律,为并行激光直写微透镜阵列的设计提供了理论指导。基于对并行激光直写系统中传统波带片阵列和折射微透镜阵列分辨力与衍射效率固有矛盾的分析,提出了基于连续深浮雕衍射透镜阵列的并行激光直写方法,采用连续浮雕衍射透镜阵列作为并行激光直写的物镜阵列,以兼顾分辨力与衍射效率,同时采用深浮雕结构降低阵列的制作难度,为并行激光直写阵列和系统设计提供一种新的设计方法。基于对激光直写制作连续浮雕衍射透镜的深度制作误差和卷积效应的分析,建立了由激光直写制作的连续浮雕衍射透镜非傍轴近似衍射聚焦模型,分析了透镜结构参数、写入光斑尺寸和扫描间距以及深度制作误差对透镜衍射聚焦特性的影响,为制作的连续浮雕衍射透镜阵列在并行激光直写中的应用提供了理论依据。为了实现写入激光和检焦激光同步、同点聚焦,提出了基于谐衍射原理的并行激光直写检焦系统设计方法,对聚焦写入透镜阵列在检焦波长处进行谐衍射设计,使聚焦写入和检焦由同一个衍射透镜阵列实现,并构建了衍射透镜阵列非傍轴近似谐振聚焦模型,进而分析了检焦波长偏差对衍射透镜阵列谐振聚焦特性的影响,为并行直写检焦系统的构建并最终实现实时同步调焦写入提供了有效手段和奠定了理论基础。最后,利用激光直写分别制作了F/7.5和F/4的连续浮雕衍射透镜阵列,并搭建了衍射透镜阵列聚焦特性测试系统,分别测试了写入激光(波长441.6nm)和检焦激光(波长670nm)入射时制作的透镜阵列的聚焦性能。实验表明,透镜阵列的聚焦特性与理论分析吻合,焦斑直径接近衍射极限值,衍射效率均优于70%,远高于波带片阵列的41%,实现了衍射效率和分辨力兼顾;同时,透镜阵列实现了写入激光和检焦激光同步、同点聚焦。更多还原

【Abstract】 Laser direct writing (LDW) is one of the important technologies used to fabricate diffractive optical elements (DOEs). With the development of DOEs for large aperture and/or array, the requirements for writing efficiency and accuracy of LDW get more and more strict. However, the throughput of traditional LDW technology with one exposured spot only is very low. With the development of multi-spots parallel laser direct writing (PLDW) technology in recent years, it is believed that multi-spots PLDW has more potential to improve the writing efficiency. However, there are still such scientific and key technique problems as it can’t take both writing resolution and diffraction efficiency into consideration, the theoretical model of diffraction focusing characteristics of microlens arrays is not precision, and the separation of writing system and defocus-detecting system makes it can’t detect focus during exposure in real time.The subject“Research on Diffractive Optical Elements Arrays with Continuous Relief for Parallel Laser Direct Writing”is to solve the scientific and key technique problems of multi-spots PLDW, and focus on the model, analysis and experiment of DOEs arrays with continuous relief. The subject provides a powerful theoretical foundation and preparation work for multi-spots PLDW with high efficiency and high accuracy.In order to study the effect of diffraction focusing characteristics of microlens arrays on the PLDW quality, we use nonparaxial approximation to analyze the focus characteristic of a single microlens, take into consideration the cross talk effect of a number of microlenses on the focusing characteristics of an array, and establish a theoretical focusing intensity model of a microlens array to describe the influence of a change in F-number (F/#) and/or center distance on the diffraction focusing characteristics of a PLDW system while incident writing laser is normal. The study would help the design of an array for PLDW use. In order to overcome the shortcomings between the writing resolution and diffraction efficiency of zone-plate arrays and/or refractive microlens arrays used for traditional PLDW technology, a PLDW method based on DOEs arrays with continuous relief is proposed. The method takes the DOEs arrays with continuous relief as PLDW objective array to take both the writing resolution and diffraction efficiency into consideration, and design the array with deep relief to make the fabrication of arrays easy, which provides a novel design method for PLDW array and system.A focusing theoretical model with nonparaxial approximation is established for DOEs with continuous relief fabricated by LDW by taken the deep fabrication error and convolution effect into consideration, and then analyzes the effect of the structure parameters, the diameter of the writing spot and the interscan distance on the diffraction focusing characteristics of low F/# DOEs with continuous relief, which establishes a firm theoretical foundation for the application of DOEs array with continuous relief for PLDW technique.In order to make writing laser and defocus-detecting laser focus synchronously into one spot, a method to design PLDW defocus-detecting system with harmonic theory is proposed. It designs the writing array for defocus detecting laser with harmonic theory to integrate the defocus-detecting array into the writing array. A harmonic focusing theoretical model with nonparaxial approximation is then established for harmonic DOEs, and further analyzes the effect of different defocus-detecting laser on the harmonic focusing characteristics.Finally, two arrays with F/# of F/7.5 and F/4 are fabricated by LDW, and then an experimental system is established to measure the focusing characteristics at normal incidence and laser wavelength of 441.6 nm and 670nm. The measurements made indicate that the experimental results agree well with theoretical results, the spot size of the array coincides well with the diffraction-limited value, and the diffraction efficiency obtained by the array excels 70%, which is much higher than the diffraction efficiency of 41% for a zone-plates array used for conventional PLDW and make it possible to further increase NA at a high diffraction focusing efficiency. Further, the DOEs arrays realize the writing laser and defocus-detecting laser focusing into synchronization.更多还原