Masafumi Miwa

Femtosecond laser-assisted three-dimensional microfabrication in silica

We demonstrate direct three-dimensional (3-D) microfabrication inside a volume of silica glass. The whole fabrication process was carried out in two steps:(i) writing of the preprogrammed 3-D pattern inside silica glass by focused femtosecond (fs) laser pulses and (ii) etching of the written structure in a 5% aqueous solution of HF acid. This technique allows fabrication of 3-D channels as small as 10mum in diameter inside the volume with any angle of interconnection and a high aspect ratio (10mum -diameter channels in a 100mum -thick silica slab).

Two-photon lithography of nanorods in SU-8 photoresist

Studies on two-photon lithography in negative SU-8 photoresist demonstrate the possibility of obtaining mechanically stable, stress-free, extended nanorods having lateral sizes of about 30 nm (corresponding to λ/25 resolution). The high resolution achievable with the given combination of materials and fabrication techniques demonstrates its potential for the fabrication of large-scale nanostructures, such as photonic crystals with photonic stop gaps at visible wavelengths.

Real three-dimensional microstructures fabricated by photopolymerization of resins through two-photon absorption

Effective energy windows for two-photon absorption (TPA) photopolymerization of resins were investigated and, with a properly selected laser pulse energy, exquisite three-dimensional (3D) microstructures with submicrometer spatial resolution were achieved. The results show the inherent utility of TPA in the fabrication of real 3D patterns. In particular, we propose and utilize a resin pre-exposure technique by which freely movable components affixed to an axle are built, demonstrating a new application of TPA in laser microfabrication.

TRANSMISSION AND PHOTOLUMINESCENCE IMAGES OF THREE-DIMENSIONAL MEMORY IN VITREOUS SILICA

We demonstrate separate readouts of three-dimensional memory by (i) transmission imaging using a conventional optical microscope and (ii) photoluminescence (PL) of the bits created by inducing optical damage within the vitreous silica. Recording was done by tightly focused (objective ×100, numerical aperture 1.3) single shot irradiation of 120 fs duration pulses at a 400 nm wavelength. For the readout, a broadband of PL at 470–600 nm was excited by 400 nm, 120 fs irradiation with pulse energy smaller by a factor of 106 compared with that for the recording. We found an erasing of the PL after 400 °C annealing, while the readability of the bits by the transmission was sustained. This shows the potential for two-bit information recording per single bit by means of separate readout procedures.

Drag of a Laser Trapped Fine Particle in a Microregion

To observe hydrodynamics in microregions, we applied laser scanning manipulation to measure the drag acting on a fine glass bead moving in mineral oil sandwiched between two glass plates (the thickness of the oil layer was a 33 and 64 µm). We measured the maximum velocity, VM, of a laser trapped bead at which the bead was released. This allowed us to quantitatively determine the drag, the drag coefficient, CD, and the Reynolds number, R, of the particle in the microregion of a viscous fluid. As a result, the minimum CDR was obtained midway between the two glass plates, and the CDR increased closer to the walls. Also, the distribution of CDR was in good agreement with the values calculated using the equation for wall effect in macroregions (over 0.1 mm).

Photonic crystal structures with submicrometer spatial resolution achieved by high-power femtosecond laser-induced photopolymerization

We demonstrate in this paper a fabrication of three- dimensional microstructures using photopolymerization of resin by two-photon absorption. When a tightly focused laser beam was scanned in a light-curling liquid, solidified rods were formed following the trace of the scanning. If the solidification was arranged to occur along the frame of a microstructure, a designed spatial pattern would be transformed into material object. Due to a quadratic dependence of photopolymerization rate on the laser pulse energy, the size of solidified voxels was controlled down to submicrometer order. Infrared transmission measurement exhibited pronounced band gap effects from thus-fabricated photonic crystal structures.

Visual communication using LED panel and video camera for mobile object

This study proposes an information transmission device constructed by a LED panel and a video camera. The LED panel displays various patterns of AR markers and micro QR codes. Then, from images taken by the video camera, some information and 3D position and pose of the camera from the LED panel are extracted. We are planning to apply this system for a communication between a radio-controlled helicopter and a base station. In this paper, we propose a method to distinguish AR markers and micro QR codes automatically, and show results of discriminated rates in the experiment.

Evaluation of fluid dynamic bearing spindle by vibration base

At present, ball bearings (BBs) are generally used in spindles of hard disk drives, but it has been known that BBs generate high-frequency vibration and acoustic noise. Hence, other types of spindles using fluid dynamic bearings (FDBs) that have high rotational accuracy and less vibration characteristics have been developed and put into practical use. FDB spindles have become common in use; nevertheless, a conventional characteristics evaluation method based on rotational accuracy, such as repeatable runout and nonrepeatable runout, is still used for FDB spindles. Since the FDB mechanism is different from BBs, we think that not only rotational accuracy, but also the shaft stiffness and the damping effect of spindle, are important in evaluating the spindle. In this study, we propose a new evaluation method for damping characteristics and frequency characteristics of FDB bearing spindles using a high-frequency vibration base. The presented method in this study is not a precious evaluation of bearing characteristics, but an evaluation method for basic mechanical comprehensive design considering tracking servo and the vibration of the disk and base in use for hard disk drives.

Three-Dimensional Microstructures Created by Laser Microfabrication Technology

Three-dimensional microstructures with aspect ratios larger than 20 and a solidified wall with a thickness down to 2.0 µm have been fabricated by the one-photon absorption photopolymerization technique. Lateral and longitudinal spatial resolutions in a single-line scanning process of as high as 1.0 µm and 0.3 µm, respectively, are reproducible. An experimental system consisting of a common picosecond pulsed laser and an optical microscope makes laser microfabrication easy to realize, implying a broad application potential.

Evaluation of quad ducted‐fan helicopter

Purpose – With the purpose of clearing up the risk to rotor blades, this paper develops a quad ducted‐fan helicopter using four ducted‐fans instead of four rotor blades in a quad rotor helicopter.Design/methodology/approach – Auto hovering test, auto cruise test, and altitude control simulations were conducted to estimate the flight performance of the quad ducted‐fan helicopter.Findings – Flight performance of the test quad ducted‐fan helicopter is almost same as a commercial quad rotor helicopter, and it succeeds to decrease the risk to the rotor blade. However, endurance is shorter than that of the quad rotor helicopter, because of the ducted‐fan characteristics.Research limitations/implications – The test quad ducted‐fan helicopter can fly for about four minutes with two packs of fourcell (16.8 V)‐2200 mAh Lipo batteries, and it needs about 3.3 times as much energy as quad rotor helicopter. The authors will improve the performance of quad ducted‐fan helicopter by aerodynamics analysis and design of duc...