Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

In this review, we describe the recent advances in supramolecular helical assemblies formed from chiral and achiral small molecules, oligomers (foldamers), and helical and nonhelical polymers from the viewpoints of their formations with unique chiral phenomena, such as amplification of chirality during the dynamic helically assembled processes, properties, and specific functionalities, some of which have not been observed in or achieved by biological systems. In addition, a brief historical overview of the helical assemblies of small molecules and remarkable progress in the synthesis of single-stranded and multistranded helical foldamers and polymers, their properties, structures, and functions, mainly since 2009, will also be described.

Supramolecular Helical Systems: Helical Assemblies of Small Molecules, Foldamers, and Polymers with Chiral Amplification and Their Functions

Invisibility devices have captured the human imagination for many years. Recent theories have proposed schemes for cloaking devices using transformation optics and conformal mapping. Metamaterials, with spatially tailored properties, have provided the necessary medium by enabling precise control over the flow of electromagnetic waves. Using metamaterials, the first microwave cloaking has been achieved but the realization of cloaking at optical frequencies, a key step towards achieving actual invisibility, has remained elusive. Here, we report the first experimental demonstration of optical cloaking. The optical 'carpet' cloak is designed using quasi-conformal mapping to conceal an object that is placed under a curved reflecting surface by imitating the reflection of a flat surface. The cloak consists only of isotropic dielectric materials, which enables broadband and low-loss invisibility at a wavelength range of 1,400-1,800 nm.

An optical cloak made of dielectrics

New microproducts need the utilization of a diversity of materials and have complicated three-dimensional (3D) microstructures with high aspect ratios. To date, many micromanufacturing processes have been developed but specific class of such processes are applicable for fabrication of functional and true 3D microcomponents/assemblies. The aptitude to process a broad range of materials and the ability to fabricate functional and geometrically complicated 3D microstructures provides the additive manufacturing (AM) processes some profits over traditional methods, such as lithography-based or micromachining approaches investigated widely in the past. In this paper, 3D micro-AM processes have been classified into three main groups, including scalable micro-AM systems, 3D direct writing, and hybrid processes, and the key processes have been reviewed comprehensively. Principle and recent progress of each 3D micro-AM process has been described, and the advantages and disadvantages of each process have been presented.

/pdf/a-review-on-3d-micro-additive-manufacturing-technologies-1kbpeb2xb5.pdf

A review on 3D micro-additive manufacturing technologies

A review of trends and limitations in hydrogel-rapid prototyping for tissue engineering

Anisotropic plasmonic responses on oblate spheroidal shape were investigated using chemically synthesized gold nanospheres. By employing the polarized transmission spectroscopy with oblique incidence, we observe 12-nm blue shift of the plasmonic resonant wavelength for gold nanospheres. The gold nanospheres with 3-nm deformation exhibited anisotropy by adsorbing on a substrate surface, resulting in the blue shift of plasmon resonant wavelength. The good agreement in measured and simulated transmission spectra leads to a precise design of gold nanospheres for plasmonic applications.

Blue shift of plasmonic resonance induced by nanometer scale anisotropy of chemically synthesized gold nanospheres

We observed the significant improvement of the figure of merit (FOM) of the longitudinal magneto-optical Kerr effect in Au/Co/Au multilayered nano rectangular patch array, in which local-mode surface plasmons were resonantly excited by the light irradiation. To demonstrate the advantage of the plasmon excitation, we compared the FOMs in both Au/Co/Au and bare Co nanostructure. Our results clearly show that the incorporation of plasmonic Au structure to magnetic Co layer is effective not only to increase rotation angle in the longitudinal magneto-optical Kerr effect but also to improve the FOM through the highly reflectance of Au.

https://iopscience.iop.org/article/10.7567/JJAP.57.110305/pdf

Plasmon assisted improvement of figure of merit of magneto-optical Kerr effect in Au/Co/Au multilayered nanorectangular patch array

https://iopscience.iop.org/article/10.7567/JJAP.57.120311/pdf

Hydrophobic assembly of gold nanoparticles into plasmonic oligomers with Langmuir–Blodgett film

PROBLEM TO BE SOLVED: To provide a photoreduction method for metal complex ions where strict controllability is not required in the control of an exposure, further, the size of the produced metal structure can be controlled, and also, there is no anxiety of reducing the spatial resolution in the size of the produced metal structure. SOLUTION: In the photoreduction method for metal complex ions where laser light is condensed and emitted on a metal complex ion-dispersed body dispersed into a material, thus the metal complex ions are photoreduced, so as to produce a metal structure, prescribed pigment is added to the material in which the metal complex ion-dispersed body is dispersed, and the laser light is condensed and emitted on the material to which the prescribed pigment is added. COPYRIGHT: (C)2007,JPO&INPIT

Photoreduction method for metal complex ions

Size, shape, and density-controlled metal nanostructure, Au nanodot lattices fabricated by electron beam lithography, were embedded in thin organic solar cell consisting of PC71BM:PCPDTBT. The effects of their size and density on device performance were examined. Even though dipole res-onances of Au nanodots were consistent with the absorption range of the active materials, there were no improvements in device performance under any sizes and densities. In addition, under high volume density of Au nanodots to PEDOT:PSS layer, the device performance was deteriorated. These results indicated that not only size and density but also other factors which determine light scattering characteristics greatly affect the device performance of solar cells. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Au nanodot lattices with well‐controlled size and density for thin organic solar cells

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