【作者】 陈浩；

【导师】 丁剑平；

【作者基本信息】 南京大学 ， 光学， 2012， 博士

【摘要】 随着激光技术以及与激光相关的光子学的发展,光作为信息的载体,其新效应、新现象和新应用对当前的科学发展和技术进步以及国防,医学,材料加工和信息传递产生越来越深远的影响。如何充分发挥光子的作用,有效地利用其新效应,对于光场的调控至关重要。光的基本性质,频率,振幅和位相已经被深入的研究并取得了和广泛的应用。而光场的偏振性质和对偏振态的调控及应用近年来才得到广泛的关注,并成为研究的热点。对光场偏振性质的调控,也就是人工调控的非均匀偏振的光场在时空的演化以及光与物质相互作用等相关领域展示了其独特新颖的性质。包括径向偏振的超衍射极限的聚焦,在等离基元透镜中激发的局域场增强,并且偏振态的空间分布为光子纠缠提供了新的自由度以及光场的偏振旋度可诱导光学轨道角动量等。此外,矢量光场在紧聚焦场中的独特性质和丰富的调控手段在光学微操纵具有广泛的前景。例如,径向的偏振光能够获得更高的光学捕捉效率,偏振调控的中空光学笼子对于低折射率的粒子能够有效捕捉等。对矢量光场的研究才刚刚起步,还存在许多没有解决的科学和技术难题。本论文以矢量光场及其效应为研究目标,对矢量光场的生成和调控及应用、新型三维光镊的提出进行了理论和实验研究,主要研究内容如下：1.新型矢量光场的生成。论文回顾了矢量光束的产生方法,提出了一种偏振和相位独立可控的新型矢量光束的实验生成方案。我们的方法基于4f系统中光波的相干分解与合成,将原有的一维光栅编码方法推广二维全息光栅编码,增加了矢量光场调控的位相自由度,可以生成偏振和位相在空间任意变化的矢量光场。利用空间光调制器对光波的实时调制特性,可以实验上动态生成出各种新颖的矢量光场。2.矢量光场的聚焦特性和目标焦场的优化设计。分析了用于聚焦场计算的Richards-Wolf矢量衍射理论,运用角谱理论重新表达了基于傅里叶变换的矢量衍射积分,通过快速算法能够方便快捷地计算焦场的分布。提出了纯偏振(polarization-only)调制的新思想,设计出入射场和焦场间的快速迭代计算方法,可以获得特定结构的焦场。提出的新方法突破了运用光波位相实现目标焦场的传统思路,为矢量焦场的调控增加了自由度。基于我们提出的空间变化的偏振和位相的矢量光场的产生方法,通过实验验证了这种新型的矢量焦场的优化设计方案的可行性和有效性。3.焦场中角动量流密度的调控。分析了位相涡旋和旋向偏振矢量同时可变的矢量涡旋光束在聚焦场中的角动量流分布特性,发现：由于涡旋相位的介入,不带有自旋角动量的矢量光束在聚焦场中可产生净的自旋角动量流密度。我们的研究表明,入射光中的涡旋位相可使得焦场中得正负自旋角动量流发生空间分离,并通过光镊实验验证了理论预测的结果。通过改变偏振和涡旋位相的拓扑荷,研究了自旋-轨道相互作用对含有自旋角动量的聚焦环带的半径的影响,通过对光阱中被捕获的液晶粒子的旋转周期观察进一步验证了自旋角动量向轨道角动量的转化。4.新型三维全息光镊的理论和实验。将三维傅里叶变换快速算法引入到全息光镊的设计,提出了新型的三维全息光镊。不同于传统的利用二维快速傅里叶变换实现离散的多平面光阱结构,我们基于三维傅里叶变换的衍射场快速计算方法,提出了三维光阱的优化迭代算法,获得了空间连续分布的三维聚焦场。通过对三维连续的焦场空间的光场调控,产生出多种新颖的三维光阱,并在实验中实现了微粒光学捕捉和空间有序堆积。更多还原

【Abstract】 With the development of laser technology and laser photonics, the photon, one of the most basic carriers of information, by contributing to much finding of new phenomena and novel effects, is playing more and more role in modern scientific and technological research, such as in national security, medicine, material processing and information processing. To take full advantage of photon and related novel effects and phenomena, the key is to manipulate the optical field. The character of light involving the phase, frequency and amplitude have been deeply explored and widely used. The vector fields as well as the manipulation of polarization state have attracted more and more interest in recent years and the research on vector fields is getting more and more attention. The inhomogeneous polarization distribution of vector field makes a great impact on the spatial-temporal evolution and the interaction of light with matter. Just name a few examples:the radially polarized field could be highly focused into a sharper spot with with subdiffraction beam size; the localized field enhancement can be realized by the use of plasmonic lens illuminated by the radially polarized field and the spatial distribution of polarization could offer another freedom for the photon entanglement; the curl of polarization could result in a new category of optical orbital angular momentum. Moreover, the capability of shaping the focal volume can be exploited for optical manipulation. The radially polarized beam has a higher trapping efficiency than the linearly polarized beam, and optical cage generated by cylindrical vector beams has the trapping capability of the low-refractive-index particles. However, the research of vector fields is fresh and there remain many scientific and technological problems to be solved. This dissertation is mainly focused on the generation, manipulation and application of the vector field and novel3D optical tweezers. The main contributions of this dissertation are as follows:1. The method to generate novel vector fields is proposed. After a review of methods to generate vector fields have been reported, we propose a convenient approach for generating arbitrary space-variant vector beam with structured polarization and phase distributions in a4f system with a spatial light modulator (SLM) and a common path interferometric arrangement. In substitution of conventional1-dimension holographic gratings with2-dimentions, phase structure of vector field is enhanced. Take advantage of SLM, optical realization of vector fields with a variety of polarization and phase configurations is obtained dynamically by modulating2D holographic grating.2. The focal properties of vector fields are discussed and the optimized design of target focal field is proposed. The mathematical derivation of the Richards-Wolf vector theory, which is used to calculate the focal properties, is carried out. We present a fast calculation of the electromagnetic field near the focus based on angular spectrum theory by using the fast Fourier transform (FFT) method. We proposed a polarization-only method of polarization shaping in the focal region with the polarization modulation of incident light. By using an iterative optimization based on a vectorial diffraction calculation relating the incident field to the focal field with the help of the FFT, we can tailor the polarization structure in the focal plane. This provides a novel way to control the vectorial feature of the focal volume with the help of polarization tailoring. Based on the method to generate the vector beams with the phase and the polarization modulated independently, the ability and flexiblity to tailor the feature of the focal volume is verified by optical experiments.3. We show that the separation of spin angular momentum flux in the focal region can occur at the focal plane illuminated by a space-variant linearly polarized beam. Such a beam carrying only the orbital angular momentum (OAM) but no SAM can develop a net SAM flux upon focusing. The radial split of the SAM flux density is mediated by the phase vortex (or OAM) and can be controlled by the topological charge of the phase vortex. The numerical simulation and the optical trapping experiment have been performed to validate the separation of the SAM flux density and spin-to-orbital conversion. Also, the radius of the focal ring is influenced by the of spin-orbital interaction in the tightly focused condition. The rotation cycle of the trapped liquid crystal particle is observed for comparison by changing the topological charge of polarization and phase.4. Theory and experiment of novel three-dimensional(3D) holographic tweezers is explored. We incorporate3D FFT into the design of holographic tweezers and propose a novel3D holographic tweezers. With our novel iterative algorithm that is based on a close inspection at the3D Fourier transform for synthesizing optical beams in the focal volume, a continuous intensity shaping within a volume becomes available. This method, which is different from the reported method of optical shaping dealing with discrete planes with2D FFT, provides a new way to develop3D-holographic optical tweezers. The perfomance of this method in optical tweezers for optical trapping and particles stacking in order are also demonstrated in our optical experiments.更多还原