As the combination of surface plasmon polariton and femtosecond laser pulse, femtosecond surface plasmon polariton has both nanoscale spatial resolution and femtosecond temporal resolution, and thus provides promising methods for light field manipulation and light–matter interaction in extreme small spatiotemporal scales. Nowadays, the research on femtosecond surface plasmon polariton is mainly concentrated on two aspects: one is investigation and characterization of excitation, propagation, and dispersion properties of femtosecond surface plasmon polariton in different structures or materials; the other one is developing new applications based on its unique properties in the fields of nonlinear enhancement, pulse shaping, spatiotemporal super-resolved imaging, and others. Here, we introduce the research progress of properties and applications of femtosecond surface plasmon polariton, and prospect its future research trends. With the further development of femtosecond surface plasmon polariton research, it will have a profound impact on nano-optoelectronics, molecular dynamics, biomedicine and other fields.

Surface plasmon polariton (SPP) provides an important platform for the design of various nanophotonic devices. However, it is still a big challenge to achieve spatiotemporal manipulation of SPP under both spatially nanoscale and temporally ultrafast conditions. Here, we propose a method of spatiotemporal manipulation of SPP pulse in a plasmonic focusing structure illuminated by a dispersed femtosecond light. Based on dispersion effect of SPP pulse, we achieve the functions of dynamically controlled wavefront rotation in SPP focusing and redirection in SPP propagation within femtosecond range. The influences of structural parameters on the spatiotemporal properties of SPP pulse are numerically studied, and an analytical model is built to explain the results. The spatiotemporal coupling of modulated SPP pulses to dielectric waveguides is also investigated, demonstrating an ultrafast turning of propagation direction. This work has great potential in applications such as on-chip ultrafast photonic information processing, ultrafast beam shaping and attosecond pulse generation.

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Surface plasmon optical tweezers based on micro- and nano-structures are capable of capturing particles in a very small spatial scale and have been widely used in many front research fields. In general, distribution of optical forces and potential wells exerted on the particles can be modulated by controlling the geometric parameters of the structures. However, these fabricated structures are irreversible once processed, which greatly limits its application in dynamic manipulation. The plasmonic field in these structures can be enhanced with orders of magnitude compared to the excitation light, offering a possibility to stimulate nonlinear responses as a new degree of freedom for dynamic modulation. Here, we theoretically demonstrate that the optical force and potential well can be modulated on account of the nonlinear Kerr effect of a gold bowtie structure under a pulsed laser with high peak power. The results verify that the trapping states, including the position, width, and depth of the potential well, can be dynamically modulated by changing intensity of the incident laser. It provides an effective approach for stable trapping and dynamic controlling of particles on nanostructure-based plasmonic trapping platforms and thus has great application potential in many fields, such as enhanced Raman detection, super-resolution imaging, and optical sensing.

The ability to draw a structured surface plasmon polariton (SPP) field is an important step toward many new opportunities for a broad range of nanophotonic applications. Previous methods usually require complex experimental systems or holographic optimization algorithms that limit their practical applications. Here, we propose a simple method for flexible generation of structured SPP field with on-chip plasmonic metalenses. The metalens is composed of multiple plasmonic focusing nanostructures whose focal shape and position can be independently manipulated, and through their superposition, SPP fields with specially designed patterns are obtained. Based on this method, we demonstrate several structured SPP fields including S- and W-shaped SPP focal fields and tunable SPP bottle beams. This work could provide new ideas for on-chip manipulation of optical surface waves, and contribute to applications such as on-chip photonic information processing and integrated photonic circuits.

On-chip manipulation of the spatiotemporal characteristics of optical signals is important in the transmission and processing of information. However, the simultaneous modulation of on-chip optical pulses, both spatially at the nano-scale and temporally over ultra-fast intervals, is challenging. Here, we propose a spatiotemporal Fourier transform method for on-chip control of the propagation of femtosecond optical pulses and verify this method employing surface plasmon polariton (SPP) pulses on metal surface. An analytical model is built for the method and proved by numerical simulations. By varying space-and frequency-dependent parameters, we demonstrate that the traditional SPP focal spot may be bent into a ring shape, and that the direction of propagation of a curved SPP-Airy beam may be reversed at certain moments to create an S-shaped path. Compared with conventional spatial modulation of SPPs, this method offers potentially a variety of extraordinary effects in SPP modulation especially associated with the temporal domain, thereby providing a new platform for on-chip spatiotemporal manipulation of optical pulses with applications including ultrafast on-chip photonic information processing, ultrafast pulse/beam shaping, and optical computing.

In recent years, singular optical beams, including optical vortex (OV) beams with phase singularities and cylindrical vector beams (CVBs) with polarization singularities, have brought new degrees of freedom for many applications. Although there have been various microscale devices for OV detection, the detection of CVBs with a microscale device is still a challenge. Here, we propose a new method for detection of CVBs with a designed on-chip plasmonic spin-Hall metalens structure. The focal position of the metalens and the splitting effect of at focus are studied in both an analytical model and numerical simulation. The results demonstrate that the metalens can not only detect different polarization orders of incident CVBs but also have an ability to distinguish radial, azimuthal and other vectorial polarization states under the same order of CVBs. This method has potential applications in compact integrated optical communication and processing systems.

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