Specially shaped Bessel-like self-accelerating beams along predesigned trajectories

Synthesis and Characterization of MOF-Derived Structures: Recent Advances and Future Perspectives

Due to their facile tunability, metal-organic frameworks (MOFs) are employed as precursors and templates to construct advanced functional materials with unique and desired chemical, physical, mechanical, and morphological properties. By tuning MOF precursor composition and manipulating conversion processes, various MOF-derived materials commonly known as MOF derivatives can be constructed. The possibility of controlled and predictable properties makes MOF derivatives a preferred choice for numerous advanced technological applications. The innovative synthetic designs besides the plethora of interdisciplinary characterization approaches applicable to MOF derivatives provide the opportunity to perform a myriad of experiments to explore the performance and offer key insight to develop the next generation of advanced materials. Though there are many published works of literature describing various synthesis and characterization techniques of MOF derivatives, it is still not clear how the synthesis mechanism works and what are the best techniques to characterize these materials to probe their properties accurately. In this review, the recent development in synthesis techniques and mechanisms for a variety of MOF derivates such as MOF-derived metal oxides, porous carbon, composites/hybrids, and sulfides is summarized. Furthermore, the details of characterization techniques and fundamental working principles are summarized to probe the structural, mechanical, physiochemical, electrochemical, and electronic properties of MOF and MOF derivatives. The future trends and some remaining challenges in the synthesis and characterization of MOF derivatives are also discussed.

Generation of the stable propagation Bessel beam and the axial multifoci beam with pure phase elements

A recently proposed method is upgraded to convert two amplitude phase modulation systems (APMSs) to pure phase elements (PPEs), for generating the stable propagation Bessel beam and the axial multifoci beam, respectively. Phase functions of the PPEs are presented analytically. Numerical simulations by the complete Rayleigh-Sommerfeld method demonstrate that the converted PPE has implemented the same optical functionalities as the corresponding APMS, in either the longitudinal or the transverse direction. Compared with the traditional APMS, the converted PPE possesses many advantages such as fabrication process simplification, system complexity reduction, production cost conservation, alignment error avoidance, and experimental precision enhancement. These inherent advantages position the PPE as an ideal choice and driving force behind further advancements in optical system technology.

Spatial Bessel-like beams along arbitrary convex trajectories based on a 3D-printed metasurface

A 3D-printed all-dielectric metasurface is presented in this Letter which can generate an accelerating beam with a circularly symmetric non-spreading transverse profile that can propagate along arbitrary convex trajectories. The curved trajectory is mapped to the corresponding direct-space spatial phases by the basic cube units with different geometrical heights. The required phase distribution is derived in detail based on the enveloping theory of differential geometry and the Bessel beam generation method. A metasurface with a preset trajectory is simulated and measured to demonstrate the validity of the phase distribution calculated by the proposed theory. The full-wave simulation and measurement results verify that the Bessel-like beam whose intensity follows a curved (off-axis) trajectory can be produced by the proposed metasurface. The generated hybrid beam merges the advantages of non-accelerating and accelerating diffractive-free beams. Therefore, the proposed metasurface has great potential in ultrahigh-speed communication, secure communication, near-field imaging, wireless energy transmission applications, and so on. The all-dielectric characteristic provides the proposed metasurface with the competitive advantages of low cost and easy large-scale processing.

Flexible trajectory control of Bessel beams with pure phase modulation

Spatial phase modulation has become an important method for the design of new self-accelerating light beams. Based on the transverse-longitudinal mapping of Bessel beam, we propose a method of pure phase modulation to directly convert a zero-order Bessel beam into a self-accelerating beam, of which the propagation trajectories can be flexibly predesigned. We experimentally demonstrate three typical types of curves that the modulated Bessel beam propagates along, and the parabolic, spiral, and teleporting self-accelarating beams are realized. The experimental results match the expected trajectory well. This method is simple to operate, and imposes fewer restrictions on the beam trajectory.

Accelerating polygon beam with peculiar features

We report on a novel kind of accelerating beams that follow parabolic paths in free space. In fact, this accelerating peculiar polygon beam (APPB) is induced by the spectral phase symmetrization of the regular polygon beam (RPB) with five intensity peaks, and it preserves a peculiar symmetric structure during propagation. Specially, such beam not only exhibits autofocusing property, but also possesses two types of accelerating intensity maxima, i.e., the cusp and spot-like structure, which does not exist in the previously reported accelerating beams with a single kind of lobes. We also provide a detailed insight into the theoretical origin and characteristics of this spatially accelerating beam through catastrophe theory. Moreover, an experimental scheme based on a digital micromirror device (DMD) with the binary spectral hologram is proposed to generate the target beam by precise modulation, and a longitudinal needle-like focus is observed around the focal region. The experimental results confirm the peculiar features presented in the theoretical findings. Further, the APPB is verified to exhibit self-healing property during propagation with either obstructed cusp or spot reconstructing after a certain distance. Hence, we believe that the APPB will facilitate the applications in the areas of particle manipulation, material processing and optofludics.