实验六 近场光学显微的系统成像原理与实验系统.docx

实验六：近场光学显微成像原理与实验系统姓名：孟超学号：38092105一、 实验目的：a) 了解近场光学显微成像的基本原理、实验方法和系统组成b) 了解近场光学显微技术在纳米科技中的应用二、 实验原理：a) 突破传统光学衍射极限b) 近场概念：传统的光学理论只研究远离光源或者物体的光场分布，一般统称为远场光学。远场光学在原理上存在着一个衍射极限，限制了利用远场光学原理进行显微时的最高分辨率而近场光学则研究距离光源或者物体一个波长范围内的光场分布。在近场光学研究领域，远场衍射极限被打破，从而可以提高显微成像的光学分辨率三、 实验思考题：a) 近场光学显微术为什么具有超过光学衍射极限的分辨率？近场光学主要探测的是束缚在物体表面的非辐射场。普通光学成像的分辨率由于受到衍射极限的限制,理论上不能超过入射光波长的一半,在可见光范围内,这一值约为200 nm。当入射光通过一个直径小于波长的小孔时, 样品上只有相当于小孔直径的范围被照射, 此时扫描成像的分辨率将取决于探针的最小尖端的直径以及探针样品间距。近场光学的本质是探测由物体衍射产生的携带低于/2空间频率的传导分量和携带高于/2空间频率的非辐射分量即:隐失场 ( evanescent field) 分量。而隐失场的有效范围仅限于一个波长以下, 所以当使用纳米尺度的探头在样品近邻扫描时,理论上可以将衍射场的非辐射分量记录下来并转换为传导分量, 从而极大地拓宽系统频带,因此可以获得超高分辨率。从而突破了光学衍射极限。b) 实现近场成像的关键技术？i. 近场测控ii. 系统集成iii. 三维扫描器iv. 光学探针四、 文献翻译：NEAR-FIELD MICROSCOPY OF SECOND HARMONIC GENERATIONIgor I. Smolyaninov, Chi H. Lee, and Christopher C. DavisElectrical Engineering Department University of MarylandCollege Park, MD 20742, USAphone: +1-301-4053255 fax: +1-3O1-314-9281e-mail: KEY WORDS : Near-field optics, second harmonic generation, piezoceramic二次谐波近场光学显微镜玛丽兰大学电子工程系关键词：近场光学，二次谐波，压电陶瓷ABSTRACTNear-field scanning optical microscopy (NSOM) allows simultaneous mapping of both the topography and optical properties of a surface with resolution below the diffraction limit. Second harmonic generation (SHG) always occurs at a surface, even for centrosymmetric media, because of symmetry breaking. By combining NSOM and SHG we can study local variations in symmetry breaking, caused for example by ferroelectric and ferromagnetic domains, and can correlate them with surface topography. We report NSOMJSHG measurements made on piezoelectric ceramics, ferromagnetic materials and periodic structures.摘要：近场光学显微镜（NSOM）可以突破衍射极限，以高分辨率把材料表面的形貌和光学特性很好的展现出来。二次谐波的产生（SHG）总是发生在表面，甚至对于中心对称的媒介也是，这是因为是破坏了对称关系。把SHG（二次谐波产生）和NSOM（近场光学显微镜）联系在一起，我们可以研究诸如铁电、铁磁的畴引起的破坏对称性方面的局域变化，然后我们可以把它们和表面形貌结合在一起。我们报告的测量是在压电陶瓷、铁磁材料和周期结构上面做的。Until recently optical second harmonic generation (SHG) has been studied only in the far-field region of samples and only with diffraction-limited optical resolution. The development of near-field scanning optical microscopy (NSOM) has opened the Possibility for studying numerous optical phenomena with a resolution well below the diffraction limit 1. In this paper we present application of NSOM techniques to the study of local SHG from different samples, such as rough metal films, gratings, piezoceramics, etc.Surface enhanced non-linear optical processes such as surface enhanced Raman and hyper-Raman scattering, two-photon luminescence, etc. have been succesfully used in surface studies and sensor applications 2. The nature of the surface enhancement phenomenon is not yet completely understood. Local field enhancement caused by surface roughness is believed to be the main factor, although the possibility of chemical enhancement has also been discussed 3. Near-field optical microscopy has the ability to solve this problem by simultaneous measurements of surface topography and optical field distributions with subwavelength resolution.直到最近，光学二次谐波发射（SHG）的研究也仅仅是开展在有光学衍射分辨率极限限制的远场样品上的。近场光学显微镜（NSOM）的发展使得大量处于衍射分辨率极限之下的光学现象的研究成为可能。在此文中，我们将展示（NSOM）的技术应用，从多种样品来分析（SHG），如粗糙的金属薄膜，光栅，压电陶瓷等。表面的光学非线性扩展过程，如表面增强拉曼散射、超喇曼散射、双光子荧光等，已经在表面研究和传感应用方面取得了很成功的应用。我们现在还不是很了解表面增强现象的本质。尽管有“化学增加”的可能性，但表面粗糙导致的局域增强仍被认为是其主要原因。近场光学显微镜可以通过同时测量次波长量级分辨率的表面形貌和光场分布，来解决这个问题。Fig. 1 Topography of a gold film (top) and SH light distribution (bottom) measured for P-polarized excitation light.图1金的形貌（顶部）和二次谐波发出的光（底部），由P极化激光测量Surface enhanced second harmonic generation (SHG) is an important example of such a surface nonlinear optics phenomenon. We have used recently developed near-field second harmonic microscopy 4 to image SHG from individual topographical defects of a gold film surface. Experimentally measured second harmonic field distributions have been compared with theoretical calculations.Metal coated diffraction gratings also exhibit surface enhanced SHG phenomena 5J. We present images of the spatial distribution of SHG from such gratings. Although the periodicity of the grating is visible in the images, a significant role in SHG is played by fine defect structure of the individual grooves.表面扩展二次谐波发射（SHG）是表面非线性光学现象中一个很重要的例子。我们应用一个最近刚刚发现的近场二次谐波显微镜来把一个金箔表面SHG从独立的形貌缺陷中成像出来。实验上对于二次谐波场的分布的测量已经与理论计算做了对比。镀金属的光栅衍射也展现出来了表面上SHG现象的加强。我们用这样的光栅展示SHG的空间分布图像。尽管在图像中，光栅的周期是可视的，SHG在fine缺陷结构独立的沟槽中扮演了一个很重要的角色。Fig.3. ST-I image of piezoceramic surface showing a hot spot of enhanced SHG due to local cavity resonance 图3 ST-I 压电陶瓷图像，展示了一个由于局域空腔共振而拓展成SHG的“热点”，Pb(ZrTii)O3 (PZT) piezoceramics have numerous applications in actuators, transducers, resonators, sensors, and motors. Crucial parameters of piezoceramic performance are hysteresis, nonlinearity, and creep. For proper application of the material, it is imperative to understand this nonlinear behavior, which depends on the quality of poling, motion of domain walls, etc.Far field observations of optical second harmonic generation (SHG) in PZT ceramic near the ferroelectric phase transition 6 demonstrated a sharp drop in SHG in the paraelectric state. The second harmonic intensity versus temperature curve corresponds qualitatively to the temperature dependence of the spontaneous polarization, which is an order parameter in the transition to the polar phase. Thus, nearfield second harmonic microscopy is ideally suited for studies of PZT nonlinearity and poling quality at the microscopic level. Pb(ZrTii)O3 (PZT) 压电陶瓷在驱动器、换能器、谐振器、传感器和电动机等方面有着广泛的应用。表现压电陶瓷性能的核心参数是滞后性、非线性性和蠕变。为了使材料适当地应用，了解它的非线性行为是非常重要的，而其非线性又是由抛光和磁畴壁的移动决定的。在PZT陶瓷的铁磁相变点附近，(SHG) 二次谐波光学激发在远场的观测表现出来一个【平行电子态的（paraelectric state）】急剧的下降。二次谐波密度相比温度曲线和与温度无关的自发极化符合很好，而这也是在极化相变点的一个序参量。因此，近场二次谐波显微是在亚显微水平研究PZT非线性化和抛光性质的最理想合适的方法。We report second harmonic images of the surface of PZT ceramic obtained using a Ti: sapphire laser (with a repetition rate 9-250 kHz, 100-fs pulse duration, and 2-.tJ pulse energy) in a nearfield microscopy setup. The polycrystalline structure of the ceramic exhibits itself in these images. Different crystallites and crystallite boundaries show different brightness of SH emission that may correspond to variations in poling. Also, hot spots of submicrometer sizes showing enhanced SHG have been detected. Linear near-field images of these hot spots reveal local cavity resonances of the fundamental light at these locations.我们报告的通过Ti: 天蓝色激光（重复率9-250kHZ，脉冲持续时间100飞秒，2-.tJ脉冲能量）在近场显微得到的PZT陶瓷的表面图像的二次谐波。陶瓷的多晶结构表现出这些图像。不同的微晶和微晶界表现出SH发射的不同的明暗，而这又与抛光中的变化相符合。“热点”的submicromeer尺度表现出来扩展SHG已经被检测到。这些“热点”的线性近场图像展现出在这些区域的基波的局域的空腔共振。REFERENCES参考：1 D.W. Pohi and D. Cour