Koji Sugioka

Investigation of photoreaction mechanism of photosensitive glass by femtosecond laser

A high-intensity femtosecond (fs) laser can fabricate complicated three-dimensional microstructures inside photosensitive glass with high spatial resolution. In this work, the mechanism of the photoreaction of the photosensitive glass to the infrared fs laser is investigated. We examine the photoinduced electron excitation process on the basis of the determination of the critical dose and a change of the optical-absorption spectrum after the fs laser irradiation. The photoreaction mechanism is discussed in comparison with the case of an ultraviolet nanosecond laser irradiation. Finally, the successive interband electron excitation through defect levels by multiphoton absorption is proposed.

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.

Laser-induced-plasma-assisted ablation for glass microfabrication

Glass is a hard transparent material with many applications in Photonics and advanced display industries. It is a high challenge to achieve crack-free glass microfabrication due to its special material characteristics. Laser-induced-plasma- assisted ablation is applied in this study to get the high quality glass microfabrication. In this processing, the laser beam goes through the glass substrate first and then irradiates on a solid target behind. For laser fluence above ablation threshold for the target, the generated plasma flies forward at a high speed. At a small target-to-substrate distance, there are strong interactions among laser light, target plasma and glass materials at the rear side of the substrate. Light absorption characteristic at the glass substrate is modified since the plasma may soften and dope into the glass in the interaction area. To have a better understanding of this processing, signal diagnostics are carried out to study the dynamic interaction. It is found that glass microfabrication is closely related to laser fluence, target-to-substrate distance, laser spot size and laser beam scanning speed. With proper control of the processing parameters, glass surface marking patterning and cutting can be achieved. With different materials as the targets, color marking of glass substrate can be obtained.

Novel technology for laser precision microfabrication of hard materials

Hybrid laser processing for precision microfabrication of hard materials, in which interaction of a conventional pulsed laser beam and another medium on the material surface leads to effective ablation, is reviewed. The main role of the medium is to produce strong absorption of the ns-laser beam tot the materials. Simultaneous irradiation of the UV laser beam with the VUV laser beam possessing extremely small laser fluence performs accurate ablation of the hard materials such as fused silica, crystal quartz, sapphire, GaN, SiC, etc. (VUV-UV multiwavelength excitation process). Metal plasma generated by the laser beam effectively assists high-quality ablation of transparent materials, leading to submicron grating fabrication and high-speed hole drilling of glass materials (laser-induced plasma-assisted ablation (LIPAA)). The detailed discussion includes ablation mechanism of hybrid laser processing and comparison of advantages and disadvantages with F2 laser ablation.

3D integration of microoptics and microfluidics in glass using femtosecond laser direct writing

We describe the fabrication of 3D microoptics and microfluidics embedded in glass using femtosecond laser direct writing. By integrating the microoptics and the microfluidics, microfluidic dye lasers three-dimensionally embedded in glass have been fabricated for the first time. By pumping the microfluidic laser, in which the microfluidic chamber was filled with laser dye rhodamine 6G dissolved in ethanol, by a frequency-doubled Nd:yttrium aluminum garnet laser, lasing action was confirmed by analyzing the emission spectra at different pumping powers. In addition, by arranging two microfluidic chambers serially in the glass, we built a microfluidic twin-laser which produces an array of two simultaneous laser emissions with one pumping laser. The integration of microoptics and microfluidic in a single glass chip paves the way toward the automatic fabrication of biophotonic chips.

THREE-DIMENSIONAL MICRO AND NANOCHIPS FABRICATED BY FEMTOSEDOND LASER FOR BIOMEDICAL APPLICATIONS

. Abstract. Three-dimensional (3D) micromachining of photosensitive glass is demonstrated by a photochemical reaction using femtosecond (fs) laser for lab-on-a-chip application. True 3D hollow microstructures embedded in the glass are fabricated by fs laser direct writing followed by heat treatment and successive wet etching. The modification mechanism of the photosensitive glass by the fs laser and advantage of this process are discussed. Various microcomponents for the lab-on-a-chip devices such as microfluidics, microvalves, microoptics, microlasers, etc. are fabricated by using this technique and their performance is examined.

Femtosecond laser microfabrication of 3D structures in Foturan glass

Currently, high throughput manufacture of Lab-on-a-chip devices integrated with both microoptics and microfluidics faces serious challenges, including assembly and packaging. Because of their different physical properties and functions, the optical and the fluidic elements are often first separately fabricated on different substrates, and then assembled into a single Lab-on-a-chip device. The alignment between the microoptical and microfluidic components requires micron-scale precision. To overcome this difficulty, we recently developed a novel laser microfabrication technique to form 3D hollow structures buried in a photosensitive glass - Foturan. The formation of both the optical and the fluidic structures were completed in a unified fabrication process. The technique is based on femtosecond laser direct writing followed by post-baking and successive chemical etching, completely eliminating the assembling procedures such as alignment, fixation, stacking, and bonding that are inherent in traditional 3D microprocessing techniques. In this paper, we describe the fabrication of a broad variety of hollow structures in Foturan glass, and the integration of these structures to build functional micro-devices. Furthermore, we will discuss how to control the fabrication resolution in three dimensions by developing novel beam focusing schemes to generate isotropic focal spot shapes inside the transparent materials.

TiN growth by hybrid radical beam-PLD for Si barrier metal

Combination of PLD and nitrogen radical beam has grown high quality TiN films on Si substrate without silicidation at the interface between TiN thin film and Si substrate even at growth temperature more than 700 degrees C. Additionally, X- ray photoelectron spectroscopy revealed that this method achieved synthesis of almost stoichiometric TiN films. Diffusion barrier characteristics of the grown film were examined by deposition of Al thin films of about 400 nm thick on the TiN grown films, followed by post-thermal treatment at 500 degrees C for 30 minutes. Scanning electron microscopy (SEM) observation and Rutherford backscattering spectroscopy analysis revealed that sharp interfaces between Al and TiN were maintained after the thermal treatment, indicating excellent property of the TiN films as Si barrier metal.

Micromachining of glass materials by laser-induced plasma-assisted ablation (LIPAA) using a conventional nanosecond laser

We report precision micromachining of fused quartz and Pyrex glass by laser-induced plasma-assisted ablation (LIPAA) using a conventional nanosecond UV or visible laser. High- quality micrograting structures with periods of 1.06 and 20 micrometers using a phase mask and a mask projection technique, respectively were fabricated by LIPAA. The Fresnel zone pattern was also produced in fused quartz. The hole with the size of 700 micrometers in diameter was fast drilled in fused quartz and Pyrex glass. A possible ablation mechanism was discussed based on the dependence of ablation metal target and glass substrate.

3D microstructuring of glass by femtosecond laser direct-writing for micro-TAS application

Three-dimensional (3-D) microstructuring of photosensitive 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 photosensitive 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. In the meanwhile, this technique is applied for integrating microoptics like micromirror and micro beam splitter in the glass chip for optical analysis of reactants produced in the microfluidics. This paper also discusses the mechanism of fs laser and photosensitive glass interaction.