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

Synthesis and factor affecting on the conductivity of polypyrrole: a short review

Three-dimensional photochemical microfabrication of poly(3,4-ethylene- dioxythiophene) in transparent polymer sheet

Conductive polypyrrole and acrylate nanocomposite coatings: Mechanistic study on simultaneous photopolymerization

Unlike conventional haptic devices, an encountered-type device is not held by a user all the time. Instead, the device stays at the location of a virtual object and waits for the user to encounter it. In this paper, we extend this concept to fingertip contacts and design an encountered-type haptic display for multiple fingertip contacts to simulate tasks of grasping an object with any shape and size. Before designing the device, we intensively observed human grasping behaviors. This observation was very helpful to determine the mechanism of the device. An encountered-type device for three-fingered grasping was actually prototyped based on our design.

Designing an Encountered-Type Haptic Display for Multiple Fingertip Contacts based on the Observation of Human Grasping Behavior.

An aqueous solution, acting as a photoinduced electron-transfer system, was prepared using tris(2,2′-bipyridyl)ruthenium complex, methylviologen, and pyrrole to demonstrate the multiphoton-sensitiz...

Multiphoton-sensitized Polymerization of Pyrrole

By focused illumination at the wavelength of 800 nm using a femtosecond laser, the tris(2,2′-bipyridyl)ruthenium complex displayed a two-photon excitation as observed by the quadratic dependence of the emission intensity on the incident laser power. Since the oxidation of pyrrole is induced by the oxidative quenching of the excited state, polypyrrole can be formed by a continuous illumination. The polymerization area showed a high spatial selectivity which can be scanned in the XYZ axis by a piezo device. In the present study, three-dimensional (3D) polypyrrole microstructures were formed in the transparent polymer sheet.

Three-dimensional photochemical microfabrication of conductive polymers in transparent polymer sheet

Conductive polymer three-dimensional microstructures were photofabricated utilizing the two-photon absorption of a sensitizer dye. The resulting three-dimensional structures were excised from the transparent polymer sheet using a micro-manipulator. The processing precisions for the vertical direction of the conductive polymer three-dimensional microstructure obtained in the transparent polymer sheet were evaluated in the present study. As a result, for the configurations of the obtained polypyrrole line deposition, the line height/line width ratios were around 5: 1; this ratio is higher than that of other UV resin works (h: w 2:4–3: 1) and the cross section distortion is not negligible for maintaining the higher reproducibility of the photofabrication.

Evaluations of vertical resolution of conductive polymer three-dimensional microstructures photofabricated in transparent polymer sheet

Stereolithography that uses a femtosecond laser was employed as a method for multiphoton-sensitized polymerization. We studied the stereolithography method, which produces duplicate solid shapes corresponding to the trajectory of the laser focus point and can be used to build a three-dimensional (3D) structure using a conductive polymer. To achieve this, we first considered a suitable polymerization condition for line stereolithography. However, this introduced a problem of irregular polymerization. To overcome this, we constructed a support in the polymerized part using a protein material. This method can stabilize polymerization, but it is not suited for building 3D shapes. Therefore, we considered whether heat accumulation causes the irregular polymerization; consequently, the reduction method of the repetition rate of the femtosecond laser was used to reduce the heating process. This method enabled stabilization and building of a 3D shape using photo-polymerization of a conductive polymer.

https://www.mdpi.com/2072-666X/6/1/96/pdf

Sub-Micrometer Size Structure Fabrication Using a Conductive Polymer

We present a new type of multi-finger haptic display in which finger contact locations can be changed by a simple mechanism Our mechanism independently represents the force for thumb, index and middle fingers and contact location changing mechanism We fabricated experimental units using carbon-fibre reinforced composite material This haptic display can be used with Spidar to easily expand the area of operation

Mechanical design of multi-finger haptic display allowing changes in contact location

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