Near-field imaging of femtosecond propagating surface plasmon and regulation of excitation efficiency

Zhao Xiang-Yu; Qin Yu-Lu; Ji Bo-Yu; Lang Peng; Song Xiao-Wei; Lin Jing-Quan

doi:10.7498/aps.70.20201827

Abstract

Near-field imaging and active control of excitation efficiency of femtosecond propagating surface plasmon (fs-PSP) are the prerequisites for its application. Here, we perform near-field imaging of fs-PSP excited at the trench etched on silver nano-film by using photoemission electron microscopy (PEEM). As an excellent near-field microscopy technique of in situ imaging with a high spatial resolution (< 20 nm), it needs neither molecular reporters nor scanning probes as required in nonlinear fluorescence microscopy in nonlinear fluorescence microscopy or scanning near-field optical microscopy, both of which may potentially bias PSP derived from such measurements. The period of the interference patterns induced by the incident femtosecond laser and the laser-induced fs-PSP and the wavelength of fs-PSP in a range of 720–900 nm of the incident laser wavelength are systematically measured. The fringe period of the interference pattern between fs-PSP and the incident laser is a range of 5.9–7.7 µm, and the wavelength of fs-PSP is in a range of 700–879 nm. The experimental results are consistent with the theoretical simulation results. Furthermore, we demonstrate that the excitation efficiency of fs-PSP can be actively controlled by adjusting the polarization direction of the incident laser in the femtosecond pump-probe experiments. Specifically, it is found that when the incident laser is polarized to 0° (p-polarization light), the excitation efficiency of PSP reaches a maximum value, and when the incident light is polarized to 90° (s-polarization light), the excitation efficiency of fs-PSP is the lowest. Unlike the simulation result by the finite difference time domain (FDTD) method, a plateau area of the intensity of the photoemission signal with the polarization direction of the incident laser appears in the femtosecond pump-probe experiment. This phenomenon is attributed to the background noise of the detection laser that masks the change of the fs-PSP excitation efficiency. In a word, this research realizes the experimental measurement of the basic parameters of fs-PSP and the manipulation of fs-PSP excitation efficiency by adjusting the polarization angle of the incident laser. This research lays a foundation for realizing the engineering manipulation of fs-PSP excitation efficiency and optimizing the performance of plasmonic devices.

Keywords:

PACS:

71.45.Gm	(Exchange, correlation, dielectric and magnetic response functions, plasmons)
73.20.Mf	(Collective excitations (including excitons, polarons, plasmons and other charge-density excitations))

Authors and contacts

School of Science, Changchun University of Science and Technology, Changchun 130022, China

Corresponding author: Qin Yu-Lu, 2296161375@qq.com ; Song Xiao-Wei, songxiaowei@cust.edu.cn ;

Funds: Project supported by the National Natural Science Foundation of China (Grant Nos. 61775021, 91850109, 11474040, 62005022, 12004052), the Education Department of Jilin Province Foundation (Grant No. JJKH20190555KJ), the Department of science and technology of Jilin Province Foundation (Grant Nos. 20200201268JC, 20200401052GX), and the China Postdoctoral Science Foundation (Grant No. 2019M661183)

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1. 引　言

飞秒传输表面等离激元(femtosecond propagating surface plasmon, fs-PSP)是传播在金属-电介质/真空界面的电磁模式. fs-PSP最显著的特性是将能量约束在亚波长尺度, 传播速度接近光速, 并且具有空前的太赫兹带宽. 这些特性使其可以作为小型化光电子器件^[1-4]中带宽信息传输的载体. 近年来等离激元器件的多种功能性已经被理论和实验证实^[1,2], 例如波导^[3-5]、多通复用^[6,7]、分束^[8,9]和聚焦^[10,11]等. 在这些方面, 深入理解fs-PSP近场特性并实现对其激发效率的调控是工程性操控和优化上述器件性能的前提条件. 由于fs-PSP的电场在垂直于样品表面方向上呈指数衰减, 且被局域在亚波长尺度, 对其进行详细的表征需要纳米空间分辨的显微技术. 在这方面, 已经开发了几种适用于探测表面等离激元时空特性的显微技术, 包括扫描阴极荧光显微镜^[12-15]、电子能量损失能谱法^[16]、荧光显微镜^[17]、相干反斯托克斯拉曼散射显微镜^[18,19], 扫描近场光学显微镜^[20,21]和光发射电子显微镜(photoemission electron microscopy, PEEM)^[22-24]. 这其中, 利用荧光显微镜或扫描近场显微镜进行近场表征时, 由于荧光分子和探针会影响样品近场分布, 进而对实验的结果产生干扰. 相比而言, PEEM可以进行实时原位成像, 具有高的空间分辨率(< 20 nm), 因此, PEEM已经被广泛应用于fs-PSP的时空成像研究^[22-24].

另一方面, 几种调控PSP激发效率的方案已经被提出. 如利用少量脊结构的相互作用, 当达到三个脊时激发效率最高^[25]. 通过金膜上的周期脊线结构阵列, 利用11个脊线阵列结构(长50 nm宽为280 nm), 沿表面周期放置, 最大可以达到20%的激发效率^[26]. 通过将光束聚焦到单个孔中的方式实现激发, 当孔尺寸大约为200 nm时激发效率最大为28%^[27]. 利用含有14个凹槽的周期光栅, 改变凹槽宽度可以实现50%的最大激发效率 ^[28]. 改变台阶高度与入射激光波长的比值^[29]或改变单个凹槽尺寸^[30]可实现对PSP激发效率的调控. 上述方案中对激发效率的调控主要依赖于样品几何结构的改变, 如阵列周期、台阶高度和凹槽宽度等. 因此, 在样品微纳结构参数固定的情况下, 难以实现对PSP激发效率的主动控制. 然而为了工程性操控等离激元器件的性能, 急切需要主动调控器件的激发效率.

本文利用飞秒TR-PEEM(time-resolved photoemission electron microscopy)实现了对fs-PSP的近场成像和fs-PSP激发效率的调控. 从PEEM图像中获取了激发光波长有720—900 nm范围内fs-PSP近电场与激发光场干涉信号的周期和fs-PSP的波长. 进一步, 通过调节入射激光的偏振方向, 实现了对fs-PSP激发效率的调控. 为了排除入射光的干扰, 采取飞秒双光束方案开展了飞秒泵浦-探测实验系统探究了入射光偏振对fs-PSP激发效率的影响, 结果表明, 通过调节入射光偏振方向可以实现对fs-PSP激发效率的主动控制, 且在激发光为P偏振时, fs-PSP的激发效率最高, 激发光为S偏振时, fs-PSP的激发效率最低. 上述实验结果都与FDTD的模拟结果一致.

2. 实验和模拟参数设置

实验　实验样品为银薄膜上刻蚀的凹槽结构. 简要的制备过程如下: 首先在洁净的硅基底上蒸镀约100 nm厚的银薄膜. 进一步利用聚焦离子束(focused ion beam, FIB)在银薄膜上刻蚀出一个1 μm × 10 μm的凹槽耦合结构. 使用钛蓝宝石飞秒激光器(Coherent, Mira900)在76 MHz重复频率下提供脉宽约130 fs的激光脉冲, 输出波长调节范围为700—900 nm, 入射光波长带宽约12 nm. 实验中使用的入射激光功率为50—80 mW. 使用焦距为20 cm的离轴抛物面镜, 相对于表面法线以65°的入射角将入射激光聚焦到样品表面, 聚焦光斑长/短轴约为60/40 µm. 入射激光的偏振角度的变化通过旋转宽带半波片来实现. 飞秒双光束泵浦-探测方案主要是在光路中引入马赫-曾德尔干涉仪将单束光脉冲分成两束相对延时可调节的光脉冲来实现. 在双光束实验时, 泵浦光和探测光的波长同为750 nm, 探测光为P偏振光. 保持探测光参数不变, 只改变泵浦光的偏振方向, 利用PEEM在探测光区域采集入射光与fs-PSP的近场干涉图像. 在本实验条件下, PSP场的趋肤深度远小于100 nm, 足以使得Ag/真空界面上的PSP与Ag/硅界面处的PSP解耦^[30]. 所以硅/Ag界面处产生的PSP并不会对Ag/真空界面上的PSP造成影响.

FDTD模拟　FDTD软件模拟过程中, 首先需要选择合适的边界条件. 周围介质为真空, 折射率为1, FDTD中边界条件为完美匹配层(PML). 光源设置为全场散射场光源. 入射激光参数(入射角、波长、偏振方向)设置与实验条件一致.

3. 结果与讨论

图1(a)所示为激发fs-PSP的实验示意图, 激光入射角度为α = 65°, 入射激光在样品表面的投影 ${{k}}_{\rm{L}}$ 垂直于凹槽长轴, 并激发fs-PSP. 激发产生的fs-PSP沿着X方向在Ag薄膜的表面传播. 图1(a)中 ${{k}}_{\rm{S}}$ 表示fs-PSP的波矢量, ${{k}}_{\rm{L}}$ 表示入射激光在样品表面投影的波矢量, ${{k}}_{\rm{B}}$ 表示干涉图案的波矢量. 入射激光为0°偏振(P偏振)光. 入射激光与其激发的fs-PSP在图1(a)所示的黑色虚线圈的位置发生近场干涉, 并形成干涉条纹图案. 我们在此区域获取fs-PSP的PEEM近场干涉图像.

$图 1 (a)激发fs-PSP的实验示意图; (b)−(e)分别表示入射激光波长为720, 760, 860 和900 nm时的PEEM图像\r\nFig. 1. (a) Schematic diagram of the experiment of exciting fs-PSP; (b)−(e) the PEEM images when the incident laser wavelength is 720 nm, 760 nm, 860 nm and 900 nm, respectively.$

图 1 (a)激发fs-PSP的实验示意图; (b)−(e)分别表示入射激光波长为720, 760, 860 和900 nm时的PEEM图像

Fig. 1. (a) Schematic diagram of the experiment of exciting fs-PSP; (b)−(e) the PEEM images when the incident laser wavelength is 720 nm, 760 nm, 860 nm and 900 nm, respectively.

下载: 全尺寸图片幻灯片

图1(b)—图1(e)给出激发光为P偏振时不同波长条件下, 捕获的PEEM图像. 激发光在样品表面的投影垂直于凹槽长轴入射, 在凹槽边缘处激发fs-PSP. fs-PSP与激发光发生近场干涉, 利用PEEM对干涉区域的近场进行成像. 入射激光波长调节范围选取为720—900 nm. 波长调节的步长为20 nm. 在图1中只选取四幅fs-PSP近场的干涉条纹图像作为演示. 由于凹槽边缘存在局域热点, 为防止PEEM探测器CCD饱和, 实验过程中将凹槽移出视野. 图1(b)中用黑色虚线框标出了凹槽所在位置. 在所有PEEM图像中都能观察到清楚的干涉图案. 这一现象源自于入射激光与其激发的fs-PSP电场的干涉. 这一结果说明了银薄膜上刻蚀的凹槽结构可以作为等离激元宽频耦合器件(720—900 nm都可激发fs-PSP). 此外根据fs-PSP的PEEM近场干涉图像, 可以获取拍頻周期大小, 并通过公式^[31]

${\lambda }_{\rm{B}}=\frac{{\lambda }_{\rm{L}}{\lambda }_{{\rm{P}}{\rm{S}}{\rm{P}}}}{\sqrt{{\lambda }_{\rm{L}}^{2}+{\lambda }_{{\rm{P}}{\rm{S}}{\rm{P}}}^{2}-2{\lambda }_{\rm{L}}{\lambda }_{{\rm{P}}{\rm{S}}{\rm{P}}}}}$

(1)

计算出fs-PSP的波长. (1)式中的 ${\lambda }_{{\rm{B}}}$ 表示fs-PSP的拍频率周期, ${\lambda }_{\rm{L}}$ 表示入射光的波长, ${\lambda }_{{\rm{P}}{\rm{S}}{\rm{P}}}$ 表示fs-PSP的波长, 具体数值如表1所列.

表 1 fs-PSP的波长及干涉条纹周期随入射激光波长改变的数值

Table 1. The value of fs-PSP's wavelength and interference fringe period changing with the incident laser wavelength.

入射光波长 ${\lambda }_{\rm{L}}/$ nm	720	740	760	780	800	820	840	860	880	900
fs-PSP拍频周期 ${\lambda }_{\rm{B}}/$ µm	5.9	6.1	6.6	6.7	7.0	7.1	7.2	7.3	7.5	7.7
fs-PSP波长的理论值 ${\lambda }_{{\rm{s}}{\rm{s}}}/$ nm	706	726	746	766	785	805	824	844	864	883
fs-PSP波长实验测得值 ${\lambda }_{{\rm{s}}{\rm{m}}}/$ nm	700	720	744	765	784	803	821	840	859	879

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| 显示表格

表1中的 ${\lambda }_{{\rm{S}}{\rm{S}}}$ 表示fs-PSP被激发的理论波长值, ${\lambda }_{{\rm{s}}{\rm{m}}}$ 表示fs-PSP被激发的实验测得值. 实验结果表明: fs-PSP的条纹间距以及fs-PSP波长变化情况一致, 均随着入射光波长的增大而增大. 并且理论结果与我们所得到的实验结果符合.

众所周知, PEEM基于光电效应对样品表面激发的光电子进行近场成像. 且

$Y\propto {E}^{2n},$

(2)

式中Y表示fs-PSP的电子产额, E为fs-PSP的近电场强度, n为光电子出射的非线性阶次. 根据(2)式可以得知, 如果获取fs-PSP的电子产额的变化趋势, 就可以得知fs-PSP近电场强度趋势, 从而可以得到fs-PSP激发效率的变化趋势. 以往研究表明, P和S偏振在相同结构中激发的fs-PSP强度有显著的差异^[32,33], 这意味着调节激光偏振方向有可能是主动调控fs-PSP激发效率的有效参数. 所以在fs-PSP近场成像的基础上, 可以通过改变不同激发光偏振方向, 获取不同激发光偏振方向下的fs-PSP近场干涉图像, 并从fs-PSP近场干涉图像中提取fs-PSP的电子产额随入射光偏振角度变化的趋势, 从而得到fs-PSP的激发效率随入射光偏振角度变化的趋势.

首先用单束激光进行实验, 即只用激发光激发fs-PSP. 实验示意图与图1(a)一致. 使得fs-PSP与激发光发生干涉, 并在干涉区域取得PEEM图像. 改变线激发光的偏振角度, 得到不同激发光偏振角度下的fs-PSP的PEEM图像, 并在图像中获取同一位置干涉条纹的fs-PSP的电子产额, 并给出fs-PSP的电子产额随入射光偏振角度变化的实验测量曲线. 接下来为了对实验结果进行验证, 利用了FDTD模拟的手段来进一步对实验结果进行模拟. 改变FDTD模拟的入射光偏振角度, 对fs-PSP的近电场强度进行模拟, 将结果与实验做对比, 并给出fs-PSP的电子产额随入射光偏振角度变化的FDTD模拟曲线, 如图2所示.

$图 2 (a)−(d) 750 nm入射激光, 随偏振角度变化的PEEM图像; (e) fs-PSP归一化的光发射电子产额随入射激光偏振角度变化的模拟和实验曲线\r\nFig. 2. (a)−(d) The PEEM images of the incident laser at 750 nm, changing with the polarization angle; (e) simulation and experimental curves of fs-PSP normalized light emission electron yield with incident laser polarization angle.$

图 2 (a)−(d) 750 nm入射激光, 随偏振角度变化的PEEM图像; (e) fs-PSP归一化的光发射电子产额随入射激光偏振角度变化的模拟和实验曲线

Fig. 2. (a)−(d) The PEEM images of the incident laser at 750 nm, changing with the polarization angle; (e) simulation and experimental curves of fs-PSP normalized light emission electron yield with incident laser polarization angle.

下载: 全尺寸图片幻灯片

图2(a)—图2(d)所示为激发光波长为750 nm, 不同偏振角度下, 捕获的PEEM图像. 偏振选取角度为0°—180°. 我们只选取其中四幅干涉条纹图案作为演示. 在捕获的PEEM图像中我们发现fs-PSP的干涉图案发生了显著的强度变化. 图2(c)中入射激光偏振角度为90°时, 干涉信号最弱激发效率最低. 图2(a)中入射激光偏振角度为0°时, 干涉信号最强激发效率最高. 这一现象源自于改变了入射激光的偏振角度, 使得fs-PSP的激发效率改变了. 这一结果表明了银薄膜上刻蚀的凹槽结构可以通过调节入射激光偏振角度来实现对fs-PSP激发效率的调控. 曲线表明fs-PSP的激发效率随入射光偏振角度的变化发生振荡变化. 发现入射光接近P偏振时激发效率最高, 接近S偏振时激发效率最低. 这说明了fs-PSP的激发效率与入射激光的偏振角度有关.

图2(e)中红色曲线为实验中实际测得的归一化fs-PSP光发射电子产额随入射光偏振角度变化的曲线. 蓝色曲线为FDTD模拟中获取的归一化fs-PSP光发射电子产额随入射光偏振角度变化的曲线. 在获取了FDTD模拟的fs-PSP近电场强度之后, 进行分析处理, 做出fs-PSP电场强度六次方 ${E}_{Z}^{6}$ 随入射光偏振变化的模拟曲线, 并与之前我们进行的实验进行分析对比. 银的功函数约为4.26 eV, 取决于样品的晶格取向和纳米结构的形貌. 因此, 在750 nm入射激光波长下, 一个光子的能量约为1.65 eV, 相应地需要吸收三个光子的能量才能实现光电子出射. 因此FDTD模拟中取 ${E}_{Z}^{6}$ 作为光发射电子产额. 图2(e)表明, 模拟曲线和实验曲线基本一致. 我们用模拟的方式重现了实验.

图2给出的实验结果显示fs-PSP的光电子产额随入射激光偏振角度变化. 但是, 目前无法直接证明fs-PSP的激发效率也如此变化. 因为有入射激光的干扰, 在单光情况下测得的光电子产额是入射光与fs-PSP共同提供的. 光与fs-PSP形成的干涉信号, 由于入射光本身激发的光电子产额同样具有偏振依赖性. 所以为了规避掉激发光对实验结果产生的影响, 又利用双光束开展了飞秒双光束泵浦-探测实验来排除入射光对实验测量fs-PSP激发效率的干扰. 探测光依然放在fs-PSP传播路径的后方(图3(a)中黑色虚线圈出的位置), 并与fs-PSP进行干涉, 并在干涉区域取得PEEM图像. 改变激发光的偏振角度, 探测光保持不变, 得到不同激发光偏振角度下的fs-PSP的PEEM图像, 并在图像中获取同一位置干涉条纹处的fs-PSP的电子产额, 并给出fs-PSP的电子产额随入射光偏振角度变化的实验测量曲线. 在模拟方面, 其他参数保持不变, 在FDTD模拟的光源外加入了点监视器, 来测量在入射光激发下纯fs-PSP的近电场强度, 与飞秒泵浦-探测实验做对比. 并给出fs-PSP的电子产额随入射光偏振角度变化的FDTD模拟曲线. 因为在实验和模拟中都排除了入射激光对实验结果的干扰, 利用飞秒泵浦-探测得到的实验结果和排除入射激光光场干扰的FDTD模拟结果会更精确, 如图3所示.

$图 3 (a)飞秒双光束泵浦-探测实验示意图; (b)−(e) 750 nm入射激光, 在探测光辐照区域, 随偏振角度变化的PEEM图像; (f) fs-PSP归一化的光发射电子产额随入射激光偏振角度变化的模拟和实验曲线\r\nFig. 3. (a) Schematic diagram of femtosecond dual-beam pumping-detection experiment; (b)−(e) the PEEM images of the incident laser at 750 nm in the area irradiated by the probe light with the polarization angle; (f) the simulation and experimental curves of fs-PSP normalized light emission electron yield with the incident laser polarization angle.$

图 3 (a)飞秒双光束泵浦-探测实验示意图; (b)−(e) 750 nm入射激光, 在探测光辐照区域, 随偏振角度变化的PEEM图像; (f) fs-PSP归一化的光发射电子产额随入射激光偏振角度变化的模拟和实验曲线

Fig. 3. (a) Schematic diagram of femtosecond dual-beam pumping-detection experiment; (b)−(e) the PEEM images of the incident laser at 750 nm in the area irradiated by the probe light with the polarization angle; (f) the simulation and experimental curves of fs-PSP normalized light emission electron yield with the incident laser polarization angle.

下载: 全尺寸图片幻灯片

图3(a)除加入探测光以及新增干涉区域为图3(a)中黑色虚线圈出的位置以外, 其余条件与图1(a)中条件一致. 在探测区域(图3(a)中黑色虚线圈出的位置)获取fs-PSP的PEEM近场干涉图像.

图3(b)—图3(e)所示为入射激光为750 nm, 不同偏振角度下捕获的探测区域的PEEM近场干涉图案. 偏振选取角度为0°—180°, 只选取其中四幅干涉条纹图案作为演示. 在探测区域可以观察到干涉图案的明暗变化, 这一现象源自于入射光的偏振角度变化. 图3(f)中红色曲线为实验中实际测得的归一化fs-PSP电子产额随入射光偏振变化的曲线. 蓝色曲线为FDTD模拟中获取的归一化fs-PSP电子产额随入射光偏振变化的曲线. 图3(f)中实验和模拟曲线的趋势与图2(e)中曲线趋势一致. 实验结果表明, 当激发光为P偏振时, fs-PSP的电子产额最高, 激发光为S偏振时, fs-PSP的电子产额最低. 因此我们推断fs-PSP的激发效率由激发光的垂直分量主导.

我们发现实验测得的曲线图底部相较于单光束激发实验测得的曲线(图2(e))出现平台区, 如图3(f)黑色椭圆形虚线位置所示. 我们获取单一探测光辐照银薄膜表面时的平均电子产额为947, 当双光束, 激发光为S偏振激发PSP时, 探测光区域的平均电子产额为992. 两者电子产额基本一致. 在入射激光偏振角度接近90°(S偏振)时, fs-PSP的激发效率低, 使得干涉区域内光电子发射强度由探测光主导, 所以曲线底部呈现随偏振角度改变极小的现象. 且归一化的光发射电子产额不接近0的原因是探测光本身提供的光发射电子产额产生的背景. 所以在曲线中并不能很好地展现出激发光接近S偏振下的fs-PSP激发效率的变化, 但总体趋势是激发光接近P偏振时fs-PSP的激发效率最高, 激发光偏振接近S偏振时fs-PSP的激发效率最低.

图3(f)中FDTD模拟获得的曲线与所做的飞秒双光束泵浦-探测实验测得的曲线趋势基本一致. 这说明改变入射光的偏振角度可以调控fs-PSP激发效率, 并且当激发光偏振接近P偏振时, fs-PSP的激发效率最高, 当激发光偏振接近S偏振时, fs-PSP的激发效率最低. 因此我们的实验结果表明, 通过调节激发光的偏振角度实现了对fs-PSP激发效率的调控.

4. 结　论

利用PEEM研究了fs-PSP的近场成像及入射激光偏振角度对fs-PSP激发效率的调控. 借助于fs-PSP近场成像实验, 得到了入射激光波长为720—900 nm时, fs-PSP与入射激光干涉图案的条纹周期为5.9—7.7 µm, fs-PSP的波长为700—879 nm. 实验测得的结果与理论模拟的结果一致. 此外, 利用飞秒双光束泵浦-探测实验, 在排除入射激光干扰的情况下, 发现当入射激光偏振角度接近0°(P偏振)时, fs-PSP的激发效率最高, 当入射激光偏振角度接近90°(S偏振)时, fs-PSP的激发效率最低. 相较于FDTD模拟结果, 飞秒双光束泵浦-探测实验测得的fs-PSP的归一化光发射电子产额随入射激光偏振角度变化的曲线在S偏振光激发附近出现平台区. 其产生的原因是探测光的背景噪声淹没了fs-PSP激发效率的变化. 总之, 该研究实现了对fs-PSP基本参数的实验测量, 并且通过调节入射激光的偏振角度, 实现了对fs-PSP激发效率的调控. 这两方面为以后等离激元器件的研发提供了一定的帮助.

感谢长春理工大学跨尺度微纳米制造教育部重点实验室在样品加工时给予的帮助.

References

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图 1 (a)激发fs-PSP的实验示意图; (b)−(e)分别表示入射激光波长为720, 760, 860 和900 nm时的PEEM图像

Figure 1. (a) Schematic diagram of the experiment of exciting fs-PSP; (b)−(e) the PEEM images when the incident laser wavelength is 720 nm, 760 nm, 860 nm and 900 nm, respectively.

DownLoad: Full-Size Img PowerPoint

图 2 (a)−(d) 750 nm入射激光, 随偏振角度变化的PEEM图像; (e) fs-PSP归一化的光发射电子产额随入射激光偏振角度变化的模拟和实验曲线

Figure 2. (a)−(d) The PEEM images of the incident laser at 750 nm, changing with the polarization angle; (e) simulation and experimental curves of fs-PSP normalized light emission electron yield with incident laser polarization angle.

DownLoad: Full-Size Img PowerPoint

Figure 3. (a) Schematic diagram of femtosecond dual-beam pumping-detection experiment; (b)−(e) the PEEM images of the incident laser at 750 nm in the area irradiated by the probe light with the polarization angle; (f) the simulation and experimental curves of fs-PSP normalized light emission electron yield with the incident laser polarization angle.

DownLoad: Full-Size Img PowerPoint

表 1 fs-PSP的波长及干涉条纹周期随入射激光波长改变的数值

Table 1. The value of fs-PSP's wavelength and interference fringe period changing with the incident laser wavelength.

入射光波长 ${\lambda }_{\rm{L}}/$ nm	720	740	760	780	800	820	840	860	880	900
fs-PSP拍频周期 ${\lambda }_{\rm{B}}/$ µm	5.9	6.1	6.6	6.7	7.0	7.1	7.2	7.3	7.5	7.7
fs-PSP波长的理论值 ${\lambda }_{{\rm{s}}{\rm{s}}}/$ nm	706	726	746	766	785	805	824	844	864	883
fs-PSP波长实验测得值 ${\lambda }_{{\rm{s}}{\rm{m}}}/$ nm	700	720	744	765	784	803	821	840	859	879

DownLoad: CSV

[1]	Gramotnev D K, Bozhevolnyi S I 2010 Nat. Photonics 4 83 Google Scholar
[2]	Ozbay E 2006 Science 311 189 Google Scholar
[3]	Wei H, Pan D, Zhang S P, Li Z P, Li Q, Liu N, Xu H X, Wang W H 2018 Chem. Rev. 118 2882 Google Scholar
[4]	Gong Y, Joly A G, Hu D, El-Khoury P Z, Hess W P 2015 Nano Lett. 15 3472 Google Scholar
[5]	Pyayt A L, Wiley B, Xia Y, Chen A, Dalton L 2008 Nat. Nanotechnol. 3 660 Google Scholar
[6]	Li X, Huang L, Tan Q, Bai B, Jin G 2011 Opt. Express 19 6541 Google Scholar
[7]	Sumimura A, Ota M, Nakayama K, Ito M, Ishii Y, Fukuda M 2016 IEEE Photonics Technol. Lett. 28 2419 Google Scholar
[8]	Chang K W, Huang C C 2016 Sci. Rep. 6 19609 Google Scholar
[9]	Hu T, Qiu H, Zhang Z, Guo X, Liu C, Rouifed M S, Littlejohns C G, Reed G T, Wang H 2016 IEEE Photonics J. 8 4802209 Google Scholar
[10]	Lemke C, Schneider C, Leißner T, Bayer D, Radke J W, Fischer A, Melchior P, Evlyukhin A B, Chichkov B N, Reinhardt C, Bauer M, Aeschlimann M 2013 Nano Lett. 13 1053 Google Scholar
[11]	Bettina F, Philip K, Daniel P, Grisha S, Meir O, Fu L W, Thomas W, Michael H H, Timothy J D, Frank-J M Z H, Harald G 2017 Sci. Adv. 3 e1700721 Google Scholar
[12]	Zu S, Han T Y, Jiang M L, Liu Z X, Jiang Q, Lin F, Zhu X, Fang Z Y 2019 Nano Lett. 19 775 Google Scholar
[13]	Zu S, Han T Y, Jiang M L, Lin F, Zhu X, Fang Z Y 2018 ACS Nano 12 3908 Google Scholar
[14]	Han T Y, Zu S, Li Z W, Jiang M L, Zhu X, Fang Z Y 2018 Nano Lett. 18 567 Google Scholar
[15]	Liu Z X, Jiang M L, Hu Y L, Lin F, Shen B, Zhu X, Fang Z Y 2018 Opto-Electron. 1 180007 Google Scholar
[16]	EL-Khoury P Z, Abellan P, Gong Y, Hage F S, Cottom J, Joly A G, Brydson R, Ramasse Q M, Hess W P 2016 The Anakyst 141 3562 Google Scholar
[17]	Wild B, Cao L, Sun Y, Khanal B P, Zubarev E R, Gray S K, Pelton M, Scherer N F 2012 ACS Nano 6 472 Google Scholar
[18]	Liu X J, Wang Y, Potma E O 2012 Appl. Phys. Lett. 101 081116 Google Scholar
[19]	Zhang W H, Fang Z Y, Zhu X 2017 Chem. Rev. 117 5095 Google Scholar
[20]	Yin L L, Vlasko-Vlasov V K, Pearson J, Hiller J M, Hua J, Welp U, Brown D E, Kimball C W 2005 Nano Lett. 5 1399 Google Scholar
[21]	Fang Z Y, Zhu X 2013 Adv. Mater. 25 3840 Google Scholar
[22]	Kubo A, Pontius N, Petek H 2007 Nano Lett. 7 470 Google Scholar
[23]	Sun Q, Zu S, Misawa H 2020 J. Chem. Phys. 153 120902 Google Scholar
[24]	Dąbrowski M, Dai Y N, Petek H 2017 J. Phys. Chem. Lett. 8 4446 Google Scholar
[25]	Ditlbacher H, Krenn J R, Hohenau A, Leitner A, Aussenegg F R 2003 Appl. Phys. Lett. 83 3665 Google Scholar
[26]	Radko I P, Bozhevolnyi S I, Brucoli G, Martı′n-Moreno L, Garcıá-Vidal F G, Boltaseva A 2008 Phys. Rev. B 78 115115 Google Scholar
[27]	Baudrion A L, León-Pérez F, Mahboub O, Hohenau A, Ditlbacher H, Garcıá-Vidal F J, Dintinger J, Ebbesen T W, Martı′n-Moreno L, R.Krenn J 2008 Opt. Express 16 3420 Google Scholar
[28]	Lu J, Petre C, Yablonovitch E, Conway J 2007 J. Opt. Soc. Am. B 24 2268 Google Scholar
[29]	Klick A, Cruz S L, Lemke C, Großmann M, Beyer H, Fiutowski J, Rubahn H G, Mendez E R, Bauer M 2016 Appl. Phys. B 122 79 Google Scholar
[30]	Zhang L X, Kubo A, Wang L, Petek H, Seideman T 2011 Phys. Rev. B 84 245442 Google Scholar
[31]	Buckanie N M, Kirschbaum P, Sindermann S, Meyer zu J, Heringdorf F 2013 Ultramicroscopy 130 49 Google Scholar
[32]	Gong Y, Joly A G, EI-Khoury P Z, Hess W P 2017 J. Phys. Chem. Lett. 8 49 Google Scholar
[33]	Qin Y L, Song X W, Ji B Y, Xu Y, Lin J Q 2019 Opt. Lett. 44 2935 Google Scholar

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Vol. 70, Issue 10 - 2021-05-20

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