表面等离激元基础

1、The Foundation Of SPPs,Contents,Part 2 The dispersion relation of SPPs,Part 3 The excitation of SPPs,Part 1 The basic concept Of SPPs,Part 1 The basic concept Of SPPs,Plasma oscillation,表面等离子体,近似认为离子不动，电子相对于离子做往回运动 等离子体内电子的集体振荡 振荡频率：,上式中，n是电子浓度，m是电子质量,Surface plasma oscillations,SPPs,表面等离子体,Surface

2、plasmon polaritons are electromagnetic excitations propagating at the interface between a dielectric and a conductor, evanescently confined in the perpendicular direction. These electromagnetic surface waves arise via the coupling of the electromagnetic fields to oscillations of the conductors elect

3、ron plasma.,The classification of SPPs,表面等离子体,1.局域的表面等离激元(Localized Surface Plasmon, LSP) 对于金属纳米颗粒,等离子振动的位置固定,其中的等离子共振模式被称作局域 化表面等离子共振。这种模式由纳米颗粒中的吸收光激发,吸收带被称作 Plasmon bands。 2.传导的表面等离激元，又称表面等离极化激元(Surface Plasmon Polariton, SPP) 在金属纳米薄膜与介质的界面上激发的表面等离激元，可以沿着薄膜远程传播。,LSP,表面等离子体,图a 在共振状态下半径为10nm的金属纳米颗粒表

4、面的光场分布情况,LSP,表面等离子体,图b 共振状态下半径为10nm的理想金属纳米颗粒的表面电场分布图,共振波长在555nm左右,The difference between LSP and SPP,表面等离子体,1.两者的色散关系不同，SPP是一种表面的传播场，而LSP是依托于某种表面结构 的局域电磁场振荡，具有一系列分立的、复数的频率，是由产生LSP的表面微结 构的尺度形状决定 2. LSP振荡可以由合适的频率和偏振的光来激发，与激励光的波矢无关，而SPP的 激发则要求激励光的频率和波矢都要和SPP匹配,LSP and SPP can be transformed into each o

5、ther,在粗糙的表面，LSP和SPP的频率接近LSP振荡可以激励SPP，SPP也可以激发LSP,LSP,SPP,能量转换,LSP和SPP之间能量的转换，对于SPP的激励起着重要作用。因为LSP不要求波矢匹配，通过LSP来激发SPP效率更高，提高了表面结构对于SPP的散射作用,Two distinctively characteristics of SPPs,表面等离子体,(c)金属/电介质界面的SPPs的示意图,(d)电磁场强度随着离界面距离增加而衰减,Part 2 The dispersion relation of SPPs,表面等离子体,如图a所示，金属和介质的分界面在z=0处，d是介

6、质的介电常数， m是金属的介电常数。SPPs沿X方向传播，考虑它分别以TE波和横磁波TM两种不同的偏振模式在界面上传播。电场垂直于图中的XOZ平面是TE波，磁场垂直于图a中的XOZ平面是TM波。,图e 金属和介质的分界面,The dispersion relation of SPPs,表面等离子体,Let us first look at TE solutions. For z0：,For Z0：,根据界面处切向电场分量和磁场分量相等的边界条件，得到：,The dispersion relation of SPPs,表面等离子体,Then we look at TM solutions. Fo

7、r z0：,For z0：,The requirement of continuity of H and E leads to：,Then we get the dispersion relation of SPPs of Metallic surface：,The dispersion relation of SPPs,The expression shows that SPPs is the surface electromagnetic wave in TM solutions. The change of dielectric constant d frequency is not b

8、ig, so that some special phenomenon associating with SPPs comes mainly from the metal.,The dispersion relation of SPPs,表面等离子体,图f SPPs色散关系,The dispersion relation of SPPs,Surface Plasma,Surface Plasma Polariton,Light Line,表面等离子体,Part 1,1. SPPs的穿透深度,The characteristic length of SPPs,（1）金属衰减深度m 根据金属趋肤深

9、度的表述，定义金属衰减深度m表示SPPs场强衰减为1/e时 的深度。,（2）介质衰减深度d 同样，定义介质衰减深度d表示SPPs场强衰减为1/e时的深度。,表面等离子体,Part 1,The characteristic length of SPPs,表面等离子体,Part 1,The characteristic length of SPPs,图g 归一化波长,表面等离子体,Part 1,The characteristic length of SPPs,表面等离子体,Part 1,The characteristic length of SPPs,图h SPPs的传播长度,表面等离子体,P

10、art 1,The characteristic length of SPPs,Part 3 The excitation Of SPPs,表面等离子体,The excitation of SPPs,Figure i. Prism coupling to SPPs using attenuated total internal reflection in the Kretschmann (left) and Otto (right) configuration. Also drawn are possible lightpaths for excitation.,1. Prism Coupling,表面等离子体,The excitation of SPPs,1. Prism Coupling,满足这一条件时，可以观察到在金属和棱镜的界面的反射率有一个极小值，这时光场和SPPs之间的耦合效率可接近100%。由于SPPs的能量集中在表面，比起入射