波导腔叠像系统及其在数字全息检测的应用研究

【作者】 樊则宾；

【导师】 李俊昌；

【作者基本信息】 昆明理工大学 ， 材料学， 2013， 博士

【摘要】 在激光材料处理及加工技术中,对激光光束的功率分布提出了较高的要求。为了实现对作用区域,激光能量的精确控制,通常希望获得矩形、均匀的激光功率分布,因此,研究激光光束的均匀化系统具有重要意义。方形波导腔叠像器具有结构简单,调节方便,能够获得边界整齐、方形分布、能量分布较均匀的光强分布。但由于激光的高相干性,不可避免伴随出现细密的干涉条纹,影响了这种系统的实际应用。如何减小和消除这些干涉条纹是一个值得研究的课题。本论文在研究方形波导腔叠像光学系统特性的基础上,提出了通过实时改变入射到波导腔叠像器入口处聚焦光点的空间位置,达到有效消除干涉条纹,提高光强均匀度的效果。通过平行板波导腔模拟实验,验证了该方法的可行性。在考虑光能的充分利用,系统便于冷却的要求,提出了在波导腔入口前面增加反射转镜和电光晶体的两种针对大功率激光光束均匀化的实用装置。近年来,随着微电子技术的飞速发展,CCD的分辨率越来越高,性价比进一步提高,这些技术的进步促进了数字全息技术的快速发展。数字全息检测技术具有非接触、灵敏度高,特别是可以实现全场检测的能力,因此备受人们的关注。目前在数字全息检测技术中,如何获得大尺寸、高质量的再现像,在彩色数字全息检测技术中如何获得尺寸统一的再现像都是研究的热点问题。本文从理论上对数字全息的可变放大率波面重建方法进行了深入研究,提出了通过频域滤波获得建立无干扰数字全息图,并将该方法用于彩色数字全息,形成彩色数字全息非插值干扰波面重建的算法,实验结果表明,再现像的质量明显改善,这为彩色数字全息技术应用于材料的无损检测提供了有益的参考。在数字全息实验中,通常是细光束经针孔滤波、扩束、准直后,变成平行光照射物体形成物光。然而,在试件尺寸较大时,必须将光束扩得很大才能照射到整个试件。由于激光束的光场分布是高斯或准高斯分布,扩束光斑的均匀性差这一弱点便显现出来。作者在对波导腔叠像器系统特性研究的基础上,在国内外首次提出将波导腔叠像器系统应用于反射式数字全息检测,即利用波导腔叠像器系统输出的矩形分布的均匀光斑照射漫反射物体,由于波导腔叠像器系统输出光斑上存在的细密干涉条纹的宽度为十几微米的数量级,而物光来自散射表面的漫反射,因此,干涉条纹不会对数字全息记录产生影响。由于物光场的均匀性明显提高,再现像的光强均匀度会更好,有利于后续通过图像处理提取测量信息,此外由于光斑区域外光强几乎为零,提高了光能的利用率,增强了物光信息,也有利于全息图的记录。为了验证以上设想,我们编制了模拟仿真软件,对物光的均匀化对再现像质量的影响进行了模拟仿真研究,模拟结果表明物光的均匀化对再现像的质量有显著影响。为了进行实验验证,我们自行设计制作了方形波导腔,并进行了数字全息对比实验。数字全息实验结果表明,物光的均匀性对再现物光的确有显著影响,经过波导腔叠像器均匀化系统输出的均匀光束作为物光照射物体可以获得比普通扩束光斑质量更高的再现物光场。波导腔叠像器系统输出光斑上存在的细密条纹不会对数字全息记录产生影响。为了证实波导腔叠像器系统确实可以应用于大尺寸物体的数字全息检测,并且可以获得比普通扩束光束照射质量更好的再现像及数字全息检测结果,论文作者自主设计、制做了两种大尺寸(约80mm)实验模型。模型采用不锈钢薄板经激光加工制成。一种是利用空气加压的立方体压力容器模型,另一种长方形容器在水的静压力下的形变模型。这两种模型的最大优点是在加、减载荷时装置具有极高的稳定性和重复性,并且两种模型的形变都是离面位移,边界处形变为零,对应于零级条纹,这两种模型还便于通过ANSYS模拟仿真进行结果比较。数字全息实验采用经波导腔叠像器系统输出的较均匀方形光斑照射实验模型,利用消零级可变放大率波面重建算法获得再现物光,再通过两幅不同载荷条件下物光的干涉形成形变场干涉条纹,根据干涉条纹得到形变场。结果表明数字全息检测的形变场的结果与ANSYS模拟仿真结果吻合甚好,表明了方形波导腔叠像器系统的确可以应用于数字全息检测。这一研究结果无疑将为大尺寸物体的数字全息检测提供了一种有效手段。最后,本文根据方形空气压力模型的最大挠度与材料的弹性模量、泊松比、厚度及长宽尺寸有关,且存在精确解析解这一事实,提出了一种测量板状金属材料弹性模量的新方法。更多还原

【Abstract】 In the application of laser material treating and processing, the high requirement is proposed for the uniformity of the laser beam distribution. In order to control the treatment region and laser energy precisely, usually, the square uniform laser distribution is required. Therefore, the study of the laser beam transformation optic system is of big significance. The square image superposition wave-guide is an optic transform system which is simple and adjustable, and the uniform square light energy distribution with shape boundary can be obtained with it. However, due to the high coherent property of laser, the fine interference fringes appear unavoidably. The existence of the intensity fringes limits the application of this optic transform system. How to eliminate these fringes is a subject worth studying. In this thesis, after studying the property of the square image superposition wave-guide system, the author has proposed a method by changing the space position of the focus spot at the entering plane of the wave-guide. The simulation experiment has performed using a parallel plane wave-guide and verified the feasibility of the approach. Considering the utilizing the laser energy efficiently and the cooling of the system, two systems suitable for practical high power laser application have been presented.With the rapid development of microelectronics, the pixels of the CCD become higher and the price become lower. The progress of these techniques has pushed the rapid development of digital holography, Digital holography has such advantages as being touch less, sensitive, and especially fulfilling the whole field measurement. Since the color digital hologram brings more information than monochromatic digital holography, for example, the measurement of three dimension displacement. Therefore the color digital holography is becoming a hot study area. At present, the wave-front reconstruction algorithm is one subject to be studied. Based on the deeply theoryitical study on the adjustable amplification reconstruction approach of the digital holography, we proposed an approach to obtain reconstruction object light field free from the zero-order diffraction interruption by filtering in frequency space. Then we applied this approach to color digital holograph and formed the non-interpolation wave-front reconstruction algorithm. The experiment result demonstrates that the quality of the reconstruction object wave field has been improved remarkably. This result has provided a useful reference for the application of color digital holography in the material testing and measurement.In the digital holography experiment, the object light waves and the reference light waves usually are obtained by laser beam filtering through pin-hole space filter, then expanding, and becoming parallel light through lens, the distribution of the expanding light is not uniform on the whole area. While the test object size is so large that it has to be placed far away from the CCD, so the light beam should be expanding even large to illuminate the whole object, and the light coming from the test object becomes very weak, under this condition, the uniformity of the light wave field distribution becomes a serious problem to affect the quality of the reconstruction image In this thesis, based on the study of the property of the square image superposition wave-guide, we first presented the ideal of applying image superposition wave-guide uniformity optical system in the digital holography, that is, the square uniform light pattern comes from image superposition wave-guide uniformity optical system is projected on the test object, the light waves scattered from the rough surface of the test object enters the window of CCD and becomes object light, since fringes separation is about several tens micrometer, the fine interference fringes on the square light pattern has no effect on the recording hologram. After passing through image superposition wave-guide optical system the light distribution become much uniform. Since the energy is concentrated within the light pattern with sharp boundary, the intensity of the object light is increased and carrying more object surface information, which is also helpful for the recording of the hologram. Due to the improvement of uniformity of the object light, the uniformity of the reconstruction image becomes better, this is valuable for the retrieve information from holograms in the proceeding treatments. In order to confirm its validation. We designed and made an image superposition wave-guide and performed digital holography experiments. The experimental results show that the quality of the reconstruction image have been improved and the fine fringes on the square light spot have no effect on the digital holography recording.In order to confirm the feasibility that the square image superposition wave-guide can be applied in the digital holography technique for large size object test, the author has designed and manufactured two test models(about80mm) with stainless steel sheet by laser processing. One is a square seal air pressure vessel; the other is a rectangular water pressure vessel. Both test models have a very high stability and repeatability while adding load or reducing load, and deformation fields are out-of-plane displacement, and the boundary is corresponding to the zero order fringes, and the results are convenient for comparing with ANSYS simulation results. The adjustable amplification reconstruction approach free from the zero-order diffraction interruption is implemented to obtain the object wave fields. The interference field of the two object waves fields under different load conditions, then the deformation field is achieved. The experiment results demonstrate that the experimental results coincide well with the ANSYS simulation results, thus approve that the square image superposition wave-guide can be applied to digital holographic detection. This research result will undoubtedly provide an effective means for digital holographic detection for large sized object. Finally, according to the fact that the maximum deformation at center of each side of square air pressure vessel has exact analytical solution and depends on the elastic modulus, Poisson ratio, thickness and the length and width geometry size, a new method for measuring the elastic modulus of plate metallic material is proposed.更多还原