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题名	超快线性衍射效应的研究
作者	席鹏
学位类别	博士
答辩日期	2003
授予单位	中国科学院上海光学精密机械研究所
导师	周常河
关键词	衍射 Dammann光栅 Talbot效应 六角阵列 超短脉冲
其他题名	Study on ultrafast linear diffractive effects
中文摘要	本论文研究了线性衍射光学在飞秒激光下的衍射效应。传统的线性衍射光学现象都是在入射光为无穷长的假设条件下作出的。从飞秒激光的研究史我们可以知道，以往的飞秒激光的研究重点放在高强度的非线性光学效应上，对线性衍射光学现象反而没有注意。飞秒激光线性衍射效应的研究具有重大意义。例如光栅在飞秒激光照射下的自成像效应的研究，它将使光栅自成像效应的研究进入新的阶段，并将为飞秒线性衍射光学这一新学科的建立奠定基础，是一项极具学术价值和应用价值的研究。在此基础上，本论文对衍射光学中的大规模点阵Dalnmann光栅，六角阵列Talbot和Zernike效应，以及超短脉冲线性衍射效应中的Talbot 效应进行了研究。主要内容如下：1．大规模阵列的Dammann光栅是Dammann光栅分束器研究的难点。基于偶数级次Dammann光栅的分析，我们设计并实现了64*64点阵Dammann光栅阵列照明。如此大规模的阵列照明器件将会对Damann光栅的实际应用起到推动作用，例如可以在光纤通信的分束祸合器中得到广泛应用。2．六角阵列是一种应用十分广泛的阵列结构，但由于其特殊的对称性，此类阵列照明器件的研究一直十分缓慢。利用开口比为1／4的六角阵列位相光栅的Zernike效应，我们实现了60×60的六角Zernike阵列照明。这一研究巧妙地利用了六角阵列周期特性，对推进六角阵列照明的研究有着积极的作用。3．通常为了数学上的方便，对Talbot效应的研究只考虑一维和二维正交的情况。但对于六角阵列，由于无法进行正交拆分而给分析带来极大困难。通过将六角阵列的复制函数进行等效正交叠加，我们得到了六角阵列Talbot效应的公共位相因子表达，并对万位相调制开口比为1／4的六角阵列位相光栅给出了半Talbot距下的Talbot照明实现条件。由于阵列周期内的六角结构无法用常规的矩形函数或圆函数描述，我们实验上观察了这一光栅的傅里叶谱。通过谱面研究发现，这一光栅满足六角阵列分数Talbot照明的条件。我们在实验上实现了效率为90.6％的六角阵列Talbot照明。这一研究在理论分析的基础上，利用实验解决了理论无法描述的难题。本工作将理论与实验结合，首次在理论上和实验上证明了六角阵列分数Talbot效应用于六角阵列照明的可行性，对六角阵列照明器的实际应用具有重要指导意义。4．本博士论文在对衍射光学和超快线性衍射效应方面进行深入综合研究的基础上，取得了如下成果：（1）基于超短脉冲线性Talbot效应的分析，我们提出了超短脉冲线性Talbot测量法。这一方法具有测量结果精确、系统极为精简、无能量和波长范围要求等特点，应用范围十分广泛。（2）对超短脉冲照明下的六角阵列Talbot效应进行了分析。结果表明，超短脉冲照明下的六角阵列Talbot照明结果的对比度和效率较连续光照明有一定下降。这一研究有助于光通信中此类照明器的性能分析。（3）平面光栅Talbot自成像效应能够比较精确地测量宽度小于20飞秒的脉冲，对大于20飞秒的脉冲需要提高探测器的灰阶值。通常探测器有限的灰阶值（例如256级）会给此类脉冲测量带来一定误差。同时，在研究位相光栅的衍射效应时，由位相深度带来的时间延迟对脉冲成像的影响不可忽略。为了分析这一问题，我们利用超短脉冲在经过位相调制时的延迟效应和Talbot效应的特性，设计了一种新型的位相振幅调制的光栅。该光栅最大的特点就是其中开口的一部分由深刻蚀或深光刻工艺加工出很深的位相台阶。这样当激光脉冲通过时就引入了一个很大的时间延迟。这个延迟量会导致对不同宽度的脉冲形成差别较大的自成像效应：对于较长脉冲，这个延迟量对最终自成像结果没有影响。对脉冲宽度与这一延迟量相当，或者短于这一延迟量的脉冲，会产生完全不同的光栅自成像结果。我们采用的光栅设计其开口比为2／3，其中1／3开口比为深度位相调制。当脉冲短到小于等于这一时间延迟时，其衍射像将发生从1:4的条纹对比度到1:1均匀照明的变化。实验中利用套刻技术和深光刻工艺制作了这一光栅，并由不同脉冲照明实验验证了这一效应。本效应的作用有两点：一是将Talbot自成像效应由高灰度级下小信号的探测变为高低对比度的探测，在很大程度上提高了测量的信噪比和灵敏度；二是平移线性Talbot测量法的敏感区域使之比较适合长脉冲，进一步扩大线性Talbot测量法的应用范围。这一成果为位相光栅的超快线性效应研究奠定了基础。
英文摘要	The dissertation concentrates on the diffraction effects under femtosecond laser illumination. The conventional linear diffractive phenomena are all based on the infinite long incidence assumption. From the history of femtosecond research, we can see that in the past the study on the femtosecond laser is mainly on the high-energy nonlinear effects, and the linear diffraction phenomena are not fully explored. The research on the femtosecond laser linear diffraction is of great significance. For example, the research on the self-imaging effect of a grating under femtosecond laser illumination will lead the grating self-imaging study to a new stage, and will establish the foundation for the new subject of femtosecond linear diffractive optics, which is of high value in both theoretical study and applications. Based on this, the large-scale array Dammann grating, the Talbot and Zernike effects of hexagonal array, and ultrashort pulse Talbot effect are studied in the dissertation. The main contents are as follows: 1. The large-scale array Dammann grating is difficult to realize. Based on the analysis of even-numbered diffraction level Dammann grating, we design and obtain a 64x64 spots Dammann grating array illuminator. Such a large-scale array illuminator can be helpful for the wide applications of Dammann grating, e.g. as a splitting coupler for optical fiber communication. Hexagonal array is a widely-used array structure. But the research on the hexagonal array illuminator is not fully explored due to the extraordinary symmetry. Employing a hexagonal array phase grating with the opening ratio of 1/4, we realize the 60x60 spots Zernike array illumination. The research employs skillfully the period feature of hexagonal array. It promotes the study of hexagonal array illumination for practical application. Usually for the convenience of mathematics, only the one-dimensional and two-dimensional orthogonal Talbot effects are considered. But for hexagonal array, the analysis is usually extremely hard due to its non-orthogonal structure. With the equivalent orthogonal summation of hexagonal replication function, we obtained the common phase factor expression of hexagonal array Talbot effect. We obtain the hexagonal array Talbot illumination condition at half Talbot plane for aπphase modulation hexagonal array grating with the opening ratio of 1/4. As the hexagonal structure within the hexagonal array period cannot be expressed with the common rectangular or circular function, we experimentally observe the Fourier spectra of the grating. From the experimental spectrums we have found that, the grating fulfills the fractional hexagonal array Talbot illumination condition. We experimentally obtain the hexagonal array illumination with the efficiency as high as 90.6%. Based on the theoretical study, we solve the mathematical problem combined with the experimental results, and for the first time it is verified that hexagonal array illumination can be realized at the fractional Talbot distance. It is meaningful to the applications of hexagonal array illuminator. 2. The dissertation studies extensively the linear diffractive optical phenomena under ultrafast laser illumination, and the achievements are as follows: Based on the study on the ultrashort pulse linear Talbot effect, we put forward the ultrashort pulse linear Talbot measuring method. The method has multiple features like high accuracy, simple system, no constraint on energy and wavelength, etc. The method has a wide application in pulse-width measurements. We experimentally analyze hexagonal array Talbot effect under ultrashort pulse illumination. The result shows that, the contrast and efficiency of ultrashort illumination are lower than those of monochromic illumination. The result is helpful for the performance analysis of such illuminators in optical communication. The self-imaging effect for the planar grating can measure accurately those pulsewidth below 20 femtoseconds, and to the pulse with pulse-width greater than 20fs, more gray levels of the detector should be required. Usually the limiting gray levels (such as 256) cannot yield the accurate measurement of these pulses. In the mean time, the temporal delay of the phase gratings caused by the phase depth cannot be ignored for the self-imaging. Considering the effect of the temporal delay that is introduced by the phase structure, we design a new type phase-amplitude modulated grating taking the advantage of the Talbot effect. The main feature of the grating is that part of the grating is able to be fabricated with a deep phase level that is made with deep etching or deep lithographic techniques. In this way, a large temporal delay is introduced when the laser pulse passes it. The delay leads a great difference of self-imaging for the specific-width pulses; for the longer pulse the delay has no result to its imaging while for those pulses whose width is comparable or lower than the delay, a complete different self-imaging is generated. The grating we designed has an opening ratio of 2/3, and the 1/3 opening ratio is the depth-phase modulation. When the pulse-width is equal to or less than the temporal delay of the grating, the contrast of the diffractive image will change from 1:4 to 1:1 for our grating. Experimentally, the amplitude and two phase levels grating is fabricated with mask alignment and deep photolithographic techniques. The method has two benefits: one is to change the detection of small signal under high gray level to high contrast detection, which improves the signal to noise ratio and the sensitivity; the other is to move the sensitive range of this linear Talbot measuring method for the easy measurement of the enhanced signals from the short to the long pulse, making it more suitable for long pulses. This method should benefit the applications of measuring the ultrashort pulse with linear Talbot measuring method. The research also establishes the foundation for the study on the linear diffraction effect under femtosecond laser illumination.
语种	中文
内容类型	学位论文
源URL	[http://ir.siom.ac.cn/handle/181231/15591]
专题	上海光学精密机械研究所_学位论文
推荐引用方式 GB/T 7714	席鹏. 超快线性衍射效应的研究[D]. 中国科学院上海光学精密机械研究所. 2003.

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