We present a detailed investigation of the effect of lens size on the focusing performance of plasmonic lenses based on metallic nanoslit arrays with variable widths. The performance parameters considered include the focal length, depth of focus (DOF), full-width half-maximum (FWHM) and the maximum intensity of the focal point. 2D FDTD simulation was utilized. The results show that all the lens parameters are greatly affected by the lens size. A larger lens size, with a total phase difference of at least 2π, will produce a better focusing behavior and a closer agreement with the design. The Fresnel number and diffraction theory can be used to explain the effect of lens size. Suggestions are provided for realization of a practical plasmonic lens using the existing nanofabrication techniques.

The development of the CHARMM lipid force field (FF) can be traced back to the early 1990s with its current version denoted CHARMM36 (C36). The parametrization of C36 utilized high-level quantum mechanical data and free energy calculations of model compounds before parameters were manually adjusted to yield agreement with experimental properties of lipid bilayers. While such manual fine-tuning of FF parameters is based on intuition and trial-and-error, automated methods can identify beneficial modifications of the parameters via their sensitivities and thereby guide the optimization process. This paper introduces a semi-automated approach to reparametrize the CHARMM lipid FF with consistent inclusion of long-range dispersion through the LennardJones particle-mesh Ewald (LJ-PME) approach. The optimization method is based on thermodynamic reweighting with regularization with respect to the C36 set. Two independent optimizations with different topology restrictions are presented. Targets of the optimizations are primarily liquid crystalline phase properties of lipid bilayers and the compression isotherm of monolayers. Pair correlation functions between water and lipid functional groups in aqueous solution are also included to address headgroup hydration. While the physics of the reweighting strategy itself is well understood, applying it to heterogeneous, complex anisotropic systems poses additional challenges. These were overcome through careful selection of target properties and reweighting settings allowing for the successful incorporation of the explicit treatment of long-range dispersion, and we denote the newly optimized lipid force field as C36/LJ-PME. The current implementation of the optimization protocol will facilitate the future development of the CHARMM and related lipid force fields.<br>

severe environmental pollution. In com parison, the physical structural color has been widely studied owing to its distinct merits, e.g., performance durability, radia tion resistance, and being environmentally friendly. Therefore, structural color has gained a great deal of interest in recent years due to its wide range of applications, e.g., color decoration, display, imaging, sensing, printing, among many others. [1][2][3][4] For the applications of structural color, wide color gamut, large viewing angle, high resolution, good flexibility, and scal able fabrication are the major issues to be addressed. Since the discovery of the extraordinary optical transmission pheno menon, [5] many kinds of structural colors have been demonstrated with a variety of plasmonic nanostructures, such as periodic subwavelength nanoholes, [6][7][8][9][10][11][12] metallic nanodisk arrays, [13][14][15][16][17] hybrid nanohole-nanodisk structures, [18][19][20][21][22][23] metallic nanoparticles, [24][25][26] and subwave length metallic gratings. [27][28][29] In general, the structural colors achieved by the afore mentioned plasmonic nanostructures highly depend on the predefined stringent geometrical and structural parameters, the realization of which all relies on complicated multistep fabrication processes, [30] such as nano imprint lithography, electronbeam lithography, reactive ion etching, and focused ion beam milling, etc. These demanding techniques result in very high fabrication cost and thus Achieving structural colors with wide color gamut, large viewing angle, and high resolution remains practically challenging. Here, proposed is an asymmetric Fabry-Perot (F-P) lossy cavity to realize subtractive colors, simultaneously featuring wide gamut, angle insensitivity, high resolution, and good flexibility. The experimental results demonstrate that the realized structural colors are insensitive to the viewing angle up to ±60°, arising from the negligible light propagation phase shift in the ultrathin lossy cavity made of an amorphous silicon (a-Si) layer; they also exhibit a wide color gamut covering the whole cyan, magenta, and yellow (CMY) color system, simply achieved through changing the thicknesses of the top metal layer and the middle lossy a-Si layer. The ultrathin configuration enables printing such colors at a deep-subwavelength resolution, and the ease of experimental fabrication enables their implementation on soft substrates. Accordingly, a 2D sketched image is printed using this cavity at a resolution of 150 000 dots per inch (dpi) in the geometrical space, corresponding to a minimum color pixel of 160 nm, well beyond the diffraction limit; a flexible structural color membrane with wide color gamut and large viewing angle is well adhered on an airplane model with a complex surface profile. Flexible Optoelectronics

Sub-diffraction-limit optical needle can be created by a binary amplitude mask through tailoring the interference of diffraction beams. In this paper, a controllable design of super-oscillatory planar lenses to create sub-diffraction-limit optical needles with the tunable focal length and depth of focus (DOF) is presented. As a high-quality optical needle is influenced by various factors, we first propose a multi-objective and multi-constraint optimization model compromising all the main factors to achieve a needle with the prescribed characteristics. The optimizing procedure is self-designed using the Matlab programming language based on the genetic algorithm (GA) and fast Hankel transform algorithm. Numerical simulations show that the optical needles' properties can be controlled accurately. The optimized results are further validated by the theoretical calculation with the Rayleigh-Sommerfeld integral. The sub-diffraction-limit optical needles can be used in wide fields such as optical nanofabrication, super-resolution imaging, particle acceleration and high-density optical data storage.

The conventional multifocal optical elements cannot precisely control the focal number, spot size, as well as the energy distribution in between. Here, the binary amplitude-type super-oscillatory lens (SOL) is utilized, and a robust and universal optimization method based on the vectorial angular spectrum (VAS) theory and the genetic algorithm (GA) is proposed, aiming to achieve the required focusing performance with arbitrary number of foci in preset energy distribution. Several typical designs of multifocal SOLs are demonstrated. Verified by the finite-difference time-domain (FDTD) numerical simulation, the designed multifocal SOLs agree well with the specific requirements. Moreover, the full-width at half-maximum (FWHM) of the achieved focal spots is close to λ/3 for all the cases (λ being the operating wavelength), which successfully breaks the diffraction limit. In addition, the designed SOLs are partially insensitive to the incident polarization state, functioning very well for both the linear polarization and circular polarization. The optimization method presented provides a useful design strategy for realizing a multiple sub-diffraction-limit foci field of SOLs. This research can find its potentials in such fields as parallel particle trapping and high-resolution microscopy imaging.