Bessel beams have attracted considerable interest because of their unique non-diffractive, self-healing characteristics. Different approaches have been proposed to generate Bessel beams, such as using axicons, diffractive optical elements, composite holograms, or spatial light modulators. However, these approaches have suffered from limited numerical aperture, low efficiency, polarization-dependent properties, etc. Here, by utilizing dielectric Huygens metasurfaces as ultrathin, compact platforms by integrating the functionalities of Dammann gratings and axicons, we successfully demonstrate multiple Bessel beam generation with polarization-independent property. The number of two-dimensional arrays can be controlled flexibly, which can enhance information capacity with a total efficiency that can reach 66.36%. This method can have various applications, such as parallel laser fabrication, efficient optical tweezers, and optical communication.

Since its invention, holography has been used to record and reconstruct all the information of an object. [1] With the advent of computer-generated holograms (CGHs), [2] the hologram generation can be done in an easier way through programming. Traditional techniques of realizing holography by using spatial light modulators (SLMs) and diffractive optical elements (DOEs) suffer

The fabrication of gold nanostructures on a dielectric substrate with a nanogap between the opposite tips is suitable for the excitation of hot spots. In this study, a novel and efficient one-step method is reported for fabricating a gold bowtie nanogap by using a spatially shaped femtosecond laser pulse. The size of the nanogap could be flexibly controlled by adjusting the pulse energy. The smallest nanogap produced by the proposed method measures 30 nm (≈1/26 of the laser wavelength). The formation mechanism of the different morphologies is investigated. Combined with a phase- and amplitude-based beam-shaping technique, the bridge could be manipulated. Both experimental surface-enhanced Raman scattering spectra and simulated finite-difference time-domain results are used to characterize the plasmonic properties of the fabricated bowtie nanogap. The manufacturing scalability of the proposed method is demonstrated through the fabrication of a matrix of nanostructure, which exhibits great uniformity, achieving a density of 2.13 × 106 devices cm–2. Large-area microgaps can be patterned on a terahertz metasurface through the proposed method. The proposed technique provides a simple, flexible, and efficient alternative method for nanogap fabrication. The method can be extensively implemented in biosensing, photovoltaics, and nanophotonics.

Designing reconfigurable metasurfaces that can dynamically control scattered electromagnetic waves and work in the near-infrared (NIR) and optical regimes remains a challenging task, which is hindered by the static material property and fixed structures. Phase change materials (PCMs) can provide high contrast optical refractive indexes at high frequencies between amorphous and crystal states, therefore are promising as feasible materials for reconfigurable metasurfaces. Here, we propose a hybrid metasurface that can arbitrarily modulate the complex amplitude of incident light with uniform amplitude and full 2π phase coverage by utilizing composite concentric rings (CCRs) with different ratios of gold and PCMs. Our designed metasurface possesses a bi-functionality that is capable of splitting beams or generating vortex beams by thermal switching between metal and semiconductor states of vanadium oxide (VO2), respectively. It can be easily integrated into low loss photonic circuits with an ultra-small footprint. Our metadevice serves as a novel paradigm for active control of beams, which may open new opportunities for signal processing, memory storage, holography, and anti-counterfeiting. IntroductionMetasurfaces have emerged as promising candidates for transforming the interactions between electromagnetic waves and matter [1][2][3][4]. By utilizing the arbitrary design freedom of metasurfaces to tailor the amplitude, phase, and polarization response, it might be possible to provide a flexible and compact platform to realize all types of functional devices, such as beam deflector, polarization converter, phase modulator, image processor and so forth [5][6][7][8][9][10][11][12]. Reconfigurability of metasurfaces typically utilize the materials whose optical properties can be modified. By integrating with functional materials such as liquid crystals, graphene (or other 2D materials) and phase change materials (PCMs), metasurfaces can obtain extra freedom of modulating the optical responses. Various reconfigurable mechanisms have been proposed, including mechanical deformation, charge carrier injection, light pumping, thermal modulation, ultra-fast nonlinear all-optical switching, etc. [13-26]. The proposed future applications in their work may bennefit the development of integrated nano-devices and multi-functional metasurfaces. Among those methods, the specific design requirements including working bandwidth, modulation depth,transition condition under external modulations should be carefully taken into account. The free carrier injection, for example, is hard to work in the optical regime for high applied voltages and low modulation depth [27][28][29][30][31][32]. While other methods may suffer from relatively huge loss and may not be very feasible for the integration of metadevices. Using the PCMs can achieve dynamic functionalities with high efficiency, feasibility, and larger working bandwidth, which makes PCMs a promising choice for reconfigurable metasurfaces.PCMs, such as germanium antimony telluride (GST), i...

The function of a laser‐shaped material depends on the geometrical morphology of its laser‐induced surface structures, which is mainly determined by the spatial intensity distribution of the laser. However, conventional patterning methods based on laser shaping techniques have shortcomings in efficiency or flexibility. A novel patterning method is developed in the present study for mask‐free and flexible fabrication of surface structures through a time‐saving spatiotemporal‐interference‐based femtosecond laser shaping technique that is based on a Michelson interferometer. The phase‐difference distribution is controlled by a spatial light modulator so that the interference intensity distribution can be modulated to user‐designed shapes. The congruence between the interference intensity distribution and the geometries on phase holograms enables the generation of phase holograms without complicated algorithms and time‐consuming calculations. This uniquely simple technique realizes flexible gray‐scale patterning on bulk material surfaces with a single femtosecond laser pulse. Thus, by using the on‐the‐fly technique, fabrication of large‐area surface structures is realized. Moreover, this technique is applied to fabricate complex structures through splicing. As an application example, three types of terahertz filters, including band‐stop and band‐pass filters, are fabricated successfully; their transmittance is in good agreement with the finite‐difference time‐domain simulation results.