Kazuhiko Shihoyama

Control of the cross-sectional shape of a hollow microchannel embedded in photostructurable glass by use of a femtosecond laser

Theoretical and experimental investigations have been made of the three-dimensional microchannel fabrication of photostructurable glass by use of a femtosecond (fs) laser. Generally, a microchannel fabricated inside glass by the scanning focal spot of a fs laser perpendicular to the direction of laser propagation assumes an elliptical shape with a cross section of large aspect ratio. We demonstrate that one can greatly reduce the aspect ratio merely by inserting a slit, which is oriented parallel to the lasers scanning direction, before the focusing lens. Computer simulations show that a more symmetrical pattern is obtained in the vicinity of the focal point with the help of such a slit, owing essentially to a diffraction effect.

Three-dimensional micro-optical components embedded in photosensitive glass by a femtosecond laser

We show that three-dimensional micro-optical components can be embedded in a photosensitive glass by a femtosecond (fs) laser. After exposure to the tightly focused fs laser beam, latent images are written inside the sample. Modified regions are developed by a postbaking process and then preferentially etched away in a 10%-dilute solution of hydrofluoric acid. After this process, hollow internal structures are formed that act as a mirror and a beam splitter. Furthermore, we find that postannealing smoothes the surfaces of the fabricated hollow structures, resulting in great improvement of their optical properties.

Optical gratings embedded in photosensitive glass by photochemical reaction using a femtosecond laser

We describe a new approach to the internal refractive index modification of glass by a femtosecond (fs) laser. The glass we used is a photosensitive glass Foturan which contains trace amounts of silver. Silver nanoparticles, which is responsible for the refractive index change, can be formed in the glass after exposed to the fs laser and then postbaked at an appropriate temperature between 500 degrees C and 550 degrees C. In this work, latent images of grating structures are first inscribed into the photosensitive glass by photochemical reaction of a tightly focused fs laser beam with an intensity much lower than the threshold of optical breakdown. After this step, no measurable diffraction can be observed by irradiating the gratings with a He-Ne laser beam. The samples are then baked at 520 degrees C for various durations from 3h to 18h. Diffraction of the optical grating embedded in the glass can now be observed, and the diffraction efficiency increases with postbaking duration, indicating that a refractive index change occurs in the modified regions. The relationship between the refractive index change and the postbaking duration is systematically investigated.

Temperature dependence of maskless ion beam assisted etching of InP and Si using focused ion beam

Temperature dependence of maskless ion beam assisted etching for InP and Si has been investigated. Thirty‐five keV Ga+ focused ion beam was irradiated on a sample surface in a chlorine gas atmosphere at various temperatures up to 200 °C. The etched surface of InP was analyzed by Auger electron spectroscopy (AES). It was observed that the etching rate for InP increased with increasing temperature and it was 20–30 times larger than that of the physical sputter etching at a temperature of 140 °C. Chlorine was detected on the InP surface etched at temperatures lower than 100 °C, but no chlorine was detected above 140 °C. For Si, 20 times enhanced etching over physical sputter etching was observed near room temperature, but the etching rate decreased with increasing sample temperature.

Laser Excitation Effects on Laser Ablated Particles in Fabrication of High Tc Superconducting Thin Films

Improvement in the characteristics of YBa2Cu3Oy superconducting thin films was performed by a second laser irradiation method. Particles in the laser ablated plume were decomposed and/or excited by the second laser irradiation. By controlling a time delay of the second laser from the ablation laser, ablated particles with average velocities of 1×106 cm/s and 2×105 cm/s were irradiated with the second laser. Notable improvement was observed when the slower ablated particles were irradiated with the second laser.

3D microfabrication in photosensitive glass by femtosecond laser

We describe a true three dimensional (3D) microfabrication of photosensitive glass by applying a femtosecond (fs) laser which works at fundamental wavelength. First, designed microstructure was written into the glass sample by a tightly focused fs laser beam (wavelength 775nm, pulse width 145±5fs, repetition rate 1kHz); next, this sample underwent a programmed heat treatment; finally it was immersed into 10% hydrofluoric (HF) acid to take an ultrasonic bath. By this approach, true 3D microstructures with embedded microchannels and microcells are directly formed inside the glass matrix, without extra bonding or adhering procedures in those planar fabrication techniques. Such an approach combines the advantages of high precision in laser microfabrication and cost-effectiveness in chemical processing, therefore, could be a promising tool in futuristic manufacture of micro total analysis systems (μ-TAS) and micro fluidic devices.

Three-dimensional micro-optical components embedded in Foturan glass by a femtosecond laser

Three-dimensional (3D) microoptical components are embedded in a photosensitive glass Foturan by a femtosecond (fs) laser. This process includes mainly three steps: (1) direct writing of latent images in the sample by the tightly focused fs laser beam; (2) baking of the sample in a programmable furnace for the formation of modified regions; and (3) etching of the sample in a 10% diluted solution of hydrofluoric acid for the selective removal of the modified regions. After this process, hollow internal structures are formed, which act as a mirror and a beam splitter. Furthermore, we find that postannealing smoothes the surfaces of the fabricated hollow structures, resulting in the great improvement of the optical properties. We examine the optical properties of the structured components using a He-Ne laser beam, and measure the optical losses at 1.55 μm wavelength.

Strong wavelength dependence of laser ablation fragments of superconductor YBa2Cu3Oy

In addition to the two groups of radiative fragments which have previously been described, two groups of nonradiative fragments are first observed in laser-ablated fragments of YBa2Cu3Oy, using a space/time-resolved optical transmittance measurement. The average velocities of the nonradiative fragments (2×105 cm/s and 2×104 cm/s) are much lower than those of the radiative fragments (5×106 cm/s and 1×106 cm/s). The yield of the nonradiative fragments increases with increasing laser wavelength, while that of the radiative fragments is nearly wavelength independent.

Fabrication of microreactors in photostructurable glass by 3D femtosecond laser direct write

Three-dimensional (3-D) microstructuring of photostructurable glass is demonstrated by using femtosecond (fs) laser for Lab.-on-chip, in other words, micro total analysis system (μ-TAS), application. The fs laser direct-write process followed by a thermal treatment and chemical etching in a HF aqueous solution produces true 3-D hollow microstructures embedded in the photostructurable glass. This technique is applied for manufacturing a microfluidic structure inside the glass. Mixing of two kinds of aqueous solutions is demonstrated in the fabricated structure. A freely movable microplate is also fabricated inside glass to control a stream of reagents in the microfluidics. To give additional functions to the fabricated microfluidics, selective metal plating of the glass i s performed by the fs laser irradiation in an electroless plating solution. This paper also discusses the mechanism of photostructurable glass modification by the fs laser.

3D microstructuring inside photosensitive glass by use of a femtosecond laser for lab-on-chip applications

In this paper we show that a femtosecond laser enables us to form true three-dimensional microstructures embedded in a photosensitive glass Foturan for lab.-on-chip applications. The Foturan glass has superior properties on transparency, hardness, chemical and thermal resistances, and biological compatibility. After exposure to the tightly focused laser beam, latent images are written inside the glass. Modified regions are developed by a post baking process and then preferentially etched away in an ultrasonic solution of 10% hydrofluoric acid in water. By use of this technique, we fabricated various true 3D microstructures including microfluidic components and micro-optics inside the Foturan glass. However, the microchannel fabricated inside glass by scanning focal spot of a femtosecond laser perpendicularly to the direction of laser propagation gets an elliptical shape with a cross section of large aspect ratio, owing essentially to a longitudinal distribution of the focal spot produced by an objective lens with numerical aperture of 0.46. We demonstrate that the aspect ratio can be effectively improved by use of a slit-assisted irradiation method. Lastly, we show that 3D micro-optics are fabricated inside the Foturan glass, which enhances the function of lab.-on-chip.