Ultrashort pulse laser has been applied to material processing which enable us to process materials with nanometer resolution and without thermal detriment. The number of papers related to this method is increasing year by year. In this paper, recent applications such as multi- photon processing, liquid immersion processing, near-field processing, self-organization process, parallel processing by SLM (spatial light modulator), non-thermal processing applied to bio materials will be introduced.

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Recently two-photon microfabrication techniques have attracted much attention due to their ability to produce complex three-dimensional micro/nanostructures and a wide variety of materials. In this paper, we briefly review the recent progress of two-photon microfabrication and introduced nanofabrication techniques using both femtosecond and deactivation laser beams. Such post processes as electroless plating and thermal treatment are also demonstrated to produce functional micro/nano devices. Finally promising applications including photonics, lab-on-a-chip, and MEMS are introduced.

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Novel laser processing methodology has been developed toward a breakthrough in the diffraction limit. It is triggered by plasmonic resonant excitation of metallic nanoparticles. The methodology falls into two categories. One is based on the enhancement effect of electromagnetic fields of incident light by localized surface plasmon. The effect can induce laser processing with a great efficiency and even 2-photon absorption. Spatial resolution less than 10 nm was demonstrated by Ueno and Misawa using a “gap-mode plasmon” in a gold nano-dimer. Obara’s group also showed a method of efficient Si processing using an isolated gold nanoparticle. The other method is based on photothermal temperature elevation of a metallic nanoparticle following electron-lattice relaxation in the metal. The fundamental mechanism of the processing is superheating of Au nanoparticles by resonant excitation, with subsequent explosive vaporization to leave nanoholes of a target polymer film. Characteristics and mechanisms of these methods are reviewed.

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On solid material under irradiation of linear polarized femtosecond laser pulses, the periodic surface structures are self-organized and oriented perpendicular or parallel to the laser polarization direction. For laser fluence levels near the ablation threshold, periodic structures have an interspace of ～0.1 λ L‒～ λ L , which is shorter than the laser wavelength λ L. The interspaces of the periodic structures depend on laser fluence and laser wavelength, and these phenomena have been explained by such models as the parametric decay model, the bidirecrtional surface plasma wave model, the plasmon polariton excitation model, and the second harmonic generation model. However, since the mechanism of the periodic structures remains unclear, further investigation is required. In this paper, we summarize the current study of the periodic surface structure induced by femtosecond laser pulses and review the several models proposed for the formation mechanism.

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We review the latest progress in the development of far-field nanostructuring technologies based on femtosecond laser direct writing. The principles for breaking through the diffraction limit in the interaction of a focused ultrafast laser beam with dielectric materials are presented, and applications of the femtosecond laser nanostructuring are discussed.

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The promising technique of laser ablation in liquid (LAL) is attracting much attention to produce nanoparticles of various materials using a simple experimental procedure. Because of the differences in the formation process of nanoparticles in LAL from those in laser ablation in gas, the important factors, which influence the formation efficiency of nanoparticles, are different between LAL and LAG. In this review, we introduce factors and methods to improve formation efficiency. The stability of colloidal nanoparticles is also an important aspect of LAL as a colloid synthesis technique. Although one of the most remarkable features of LAL is that pure colloids are obtained, the stability and the usability of colloids are greatly improved by stabilizing reagents.

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One-dimensional (1D) semiconductor crystal growth has attracted much attention for future nanoscale electronic and optoelectronic devices because of their properties which are difficult to realize using bulk materials. A review on current progress in laser-assisted bottom-up growth of many kinds of 1D semiconductor nanocrystals and its principle growth mechanism has been described. Among many semiconductor materials, zinc oxide (ZnO) is one of the most promising candidates for optical and photonic devices due to excellent luminescence properties. In this article, a novel growth method of ZnO nanocrystals, known as nanoparticle-assisted pulsed laser deposition (NAPLD) has been reviewed. Further, a novel approach of position-controlled growth of ZnO nanocrystals by non-contact laser irradiation without a catalyst has been discussed.

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In this paper, control of interference pattern of four, six beams or eight beams at two wavelengths is shown. The patterns can be controlled by phase and amplitude variation between beams. In addition, a variety of 2D- and 3D- nanostructure in matrix, such as nanobump, nanodrop, nanowhisker, MHA (Metallic Hole Array), designed pattern, bimetallic-nanobelt, duplicated periodic structure of interference pattern and LIPSS (Laser-induced periodic structure) are shown.

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Periodic nanostructures were created on a polyethylene terephthalate (PET) film surface with a femtosecond laser to control cell spreading. Controlling cell spreading on PET surface would contribute to the creation of advanced biomaterials. The PET film was bonded with the Si wafer, as a pre-treatment. A silicon wafer was irradiated with the femtosecond laser through the PET film. After the irradiation, periodic nanostructures were produced on the PET film surface. The period and groove depth of the periodic nanostructure on the PET were about 600 nm and 100 nm, respectively. In a cell test on the PET film, cell spreading was observed with a fluorescence microscope. 71% of cells were spread along the grooves on the PET.

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Laser-induced dot transfer (LIDT) provides a method for arranging a nano- or microdot at a given position on substrates under room-temperature atmospheric conditions. Based on this method, we have developed site- and size-controlled micropatterning of functional dots. The downsizing of dots can be realized by decreasing source film thickness and/or laser spot size, resulting in FeSi2 nanodot array with a dot diameter of about 500 nm. In this work, the adhesion of dots to a silica glass substrate surface was also examined by the immersion of a FeSi2 microdot array into 5% HF solution followed by washing in ultrapure water. As a result, there was no drastic change in dot filling rate for the array immersed for 2 min, suggesting that the dots were not simply placed on the substrate without being fixed. They might be attached to the substrate surface through a binding force induced via LIDT process.

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