Eager: Demonstration of Space-Time Surface Plasmon Polaritons

基于纳米技术的光学传感器一直是一个重要的技术领域，因为这些设备对周围环境的变化非常敏感。然而，该技术的有效性仅限于在非常有限的范围内感测这些干扰。PI将领导对一种新型现象的研究，这种现象可能导致显着增强的光学传感器，可以在显着延长的距离上工作。研究活动将提供一个机会，培训和指导至少一名属于实验纳米光学和相关数据分析的代表性不足的群体的研究生。此外，学生将协助以各种学术渠道的形式广泛传播所有成果，包括技术同行评审出版物，会议演示和研讨会。涉及异国情调的光束纳米光学的概念将被纳入一个新的入门，动手光学显微镜课程，目标是本科毕业生和研究生从各个工程学科。传统的表面等离子体激元（SPP），存在于金属-电介质界面，是基于由光学平面波或高斯光束激发。因此，SPP在近红外区沿着该界面沿着传播高达几百微米（可见光区的长度要短得多），并从表面消失。在这里进行的研究调查时空表面等离子激元（ST-SPPs）的存在，预计将表现出扩展的传播沿着金属-电介质界面。ST-SPP利用新开发的时空（ST）波包，已被实验证明在任何介质中沿沿着一个横向维度无衍射和无色散。ST波包是沿着（通常）两个可分离的自由度（在这种情况下是空间频率和波长）的光场“经典纠缠”的表现。虽然传统的SPP仅沿表面上的横向平面中的一个方向沿着被限制，它们沿该方向沿着传播，但预期ST-SPP被限制在两个横向维度中。因此，代替SPP经历的1-D衍射扩展，ST-SPP将保持受限并且继续沿着基本上无衍射的表面传播。在存在吸收损耗的情况下，存在预期的ST-SPP强度的降低，但是衍射对ST-SPP的影响保持不变。因此，ST-SPP可以传播仅受金属损耗限制的长距离，而SPP将受金属损耗和衍射两者限制。此外，与基于高斯的SPP波包相反，ST-SPP将不经历任何时间扩展，即，分散体此外，与Airy等离子体不同，所提出的ST-SPP以直线行进。因此，ST-SPP的特性类似于等离子体子弹。除了证实ST-SPPs的存在外，这里进行的基础研究旨在证明ST-SPPs可以在更远的距离上旅行（无损耗时约为300倍，有损耗和严格限制时可高达约1000倍），和ST的波束转向-该奖项反映了NSF的法定使命，并已被认为是值得通过使用评估支持基金会的学术价值和更广泛的影响审查标准。

Optical sensors based on nanotechnology have been an area of technological importance because of the extreme sensitivity of these devices to changes in the surrounding environment. However, the effectiveness of this technology is limited to sensing these disturbances over a very limited range. The PI will lead an investigation of a new type of phenomenon that could lead to significantly enhanced optical sensors that can work over significantly extended distances. The research activity will provide an opportunity to train and mentor at least one graduate student belonging to an underrepresented group in experimental nano-optics and associated data analysis. Moreover, the student will assist in the broad dissemination of all results in the form of various academic channels including technical peer-reviewed publications, conference presentations, and seminars. Concepts in nano-optics involving exotic optical beams will be incorporated into a new introductory, hands-on optical microscopy course that targets undergraduate seniors and graduate students from various engineering disciplines. Traditional surface plasmon polaritons (SPPs), which exist at a metal-dielectric interface, are based on excitation by either an optical plane wave or Gaussian beam. As a result, SPPs propagate along this interface up to a few hundred microns in the NIR regime (and much shorter lengths in the visible) and evanescently decay away from the surface. The research carried out here investigates the existence of space-time surface plasmon polaritons (ST-SPPs), which are expected to exhibit extended propagation along a metal-dielectric interface. ST-SPPs utilize newly developed space-time (ST) wave packets, which have been shown experimentally to travel diffraction-free and dispersion-free in any medium along one transverse dimension. ST wave packets are a manifestation of ‘classically entangling’ an optical field along (typically) two separable degrees-of-freedom, which in this case are spatial frequency and wavelength. While traditional SPPs are confined along only one direction in the transverse plane on the surface, which they propagate along, ST-SPPs are expected to be confined in two transverse dimensions. Thus, in lieu of the 1-D diffractive spreading that SPPs undergo, ST-SPPs will remain confined and continue to propagate along the surface essentially diffraction-free. In the presence of absorptive loss, there is the expected reduction in intensity of the ST-SPP, but the effect of diffraction on the ST-SPP remains unchanged. Thus, an ST-SPP could propagate long distances limited by the metal loss only as opposed to an SPP which will be limited by both metal loss and diffraction. Moreover, in contrast to a Gaussian-based SPP wave packet, a ST-SPP would not undergo any temporal spread, i.e., dispersion. In addition, unlike Airy plasmons, the proposed ST-SPPs travel in a straight line. Thus, the characteristics of ST-SPPs would be akin to a plasmonic bullet. In addition to confirming the existence of ST-SPPs, the fundamental studies carried out here aims to demonstrate that ST-SPPs can travel at much greater distances (~300x without loss, and up to ~1000x with loss and tight confinement) than SPPs, and beam steering of ST-SPPs on a surface at femtosecond time scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.