We examined the physical chemistry underlying a wet chemical etching-assisted femtosecond laser microfabrication technique. Close scrutiny of etching reagents and the etching process has led to further refinement of the method for practical use such as microchips for chemical total analysis systems (μ-TAS). Microchannels as long as a centimeter scale with less than 60 μm diameter (aspect ratio of ∼200) were fabricated inside vitreous silica substrates. In this regard, we demonstrated that a concentrated aqueous solution of KOH is advantageous over commonly used aqueous HF because of least saturation behavior in elongating channel structures. Resultant nearly twice as large the etching selectivity of KOH as that of HF allowed substantial penetration depths within the laser-modified volume while leaving the unmodified regions practically intact. Furthermore, the mechanism of laser-modification that permits highly selective wet etching was investigated by photoluminescence and confocal Raman spectral measurements of the irradiated microvolumes. Based on the experimental results, we propose that the formation of a Si-rich structure is responsible for the remarkably enhanced etching rate of aqueous KOH, in addition to the densificaton of the silica structure previously advocated for the mechanism of waveguide formation.

We observed the formation of subwavelength periodic strained layers associated with nanovoids in the cross section of femtosecond laser-irradiated lines written inside 4H-SiC single crystals. Both conventional and high-voltage transmission electron microscopies were carried out for microstructural analyses. The cross section of the irradiated lines consists of four to six groups of fine periodic structures. Each group is composed of strained layers with a typical spacing of 150 or 300 nm. The layers extend along the irradiated lines, aligned parallel to the electric field of the laser light. Tiny voids approximately 20 nm in diameter are found in the layers.

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We have fabricated optical rotators inside a silica substrate and rotated them by a laser trapping technique. The fabrication method used was femtosecond laser-assisted etching, i.e., modification of the host material by irradiation with femtosecond laser pulses along a predesigned pattern, followed by selective chemical etching. The rotators, which consist of the same material as the substrate, can move inside the microcavity but cannot get out. The rotation speed was proportional to the trapping laser power, and the maximum achieved was about 100 rpm. Such rotators will be applicable to micro-total-analysis systems and microfluidics.

An overview of the vast array of the laser material processing techniques is presented as they apply to fabricating structures in the micro and nanometer scale length domains. The overview covers developments from the past 20 years, and encompasses demonstrated processes where the use of the inherent properties of lasers has led to increased fidelity in the processing of materials. These demonstrated processes often use inventive approaches that rely on derivative aspects of established primary principals that govern laser/material interaction phenomena. By using these nuances in concert with the unique properties of lasers, a high level of finesse has been demonstrated in materials processing. The overview highlights by the use of selective examples those processes or techniques that appear to show scalability to the industrial environment.Keywords: laser processing, overview, micro/nanofabrication, IntroductionLasers have been used in materials processing for over 50 years, though in the early days, work was more focused on mitigating laser damage in materials as opposed to the processing of materials. However, the application of lasers to controllably alter materials was recognized early and as an industry, laser processing applications now lead world wide laser sales. The calendar 2005 totals for laser process tooling is near $6.0B USD 1 . Consequently, laser materials processing can no longer be considered a niche industry as there appears to be an increasing demand to apply laser processing solutions to manufacturing for specific value added segments. Commensurate with these industry trends is the fact that the number of conferences devoted to laser material processing continues to grow. This is a normative signal that industry is currently more amenable to applying laser based solutions into the manufacturing process. There are many factors that have contributed to this change in view over the course of the past 2 decades, the primary one being the advance of laser technology with a commensurate increase in system reliability. Figure 1 shows a graph that depicts the number of world wide publications per year that mention laser material processing in the title or the abstract. The data spans nearly 40 years. The results represent a lower value to the total number of publications because there could be publications that discuss laser material processing research or development but fail to mention it in the title or abstract. The data is from an assembled series of databases that includes not only journal articles but also government sponsored research articles from the USA, Japan (e.g. MITI), Germany (e.g. BMFT), France (e.g. CNRS), Canada (e.g. NRC), UK (e.g. Department of Industry) and others. This data supports the conclusion that laser material processing is an established field that could support nearly 400 publications per year.In this paper we explore a small segment of the overall laser material processing industry, namely the use and application of lasers in micro and nanofabrication. By their ver...