Silicon (Si) photonics technology, which has a DNA of Si electronics technology, would provide a promising photonics-electronics integration platform with superior mass-productivity and cost performance. Using this technology, various photonic devices, such as fi lters, modulators and detectors, have been developed and are now monolithically integrated on a Si chip. Moreover, photonicselectronics convergence is now being developed intensively. Ultra-compact photonics-electronics module based on this technology would signifi cantly contribute to the construction of energy-effi cient, cost-effective information trading systems. Considering material characteristics of Si and present fabrication technology, however, these advantages show trade-off relation to device performances. In this paper, at fi rst, we review the present status of Si photonics technology, and reveal its pros and cons. Then, we discuss about technological obstacles to the practical applications of Si photonics as a multipurpose photonic integration platform.

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Due to their extremely high peak intensity, ultrashort laser pulses can readily initiate the multi-photon process at the focal point inside transparent materials and directly and precisely join them via localized melting without any intermediate layer under a room-temperature environment. These features are well fi tted for the hermetic sealing of such photonics devices as solar cells, LCDs, and MEMS. We review the recent advances of the welding or joining of glass substrates with an ultrashort laser micro (ULM) joining technique. After briefl y discussing its principles, we address such critical issues of it as the pulse repetition rate, the use of the fi lamentary propagation of pulses, residual stress, glass-metal joining, the joined glass-metal interface, and the temperature dynamics. Finally, we introduce trial applications to industrial solar cell panels and the glass-Si wafer joining.

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In this paper we review recent progress in ultrafast laser processing with applications in electronics industry. Ultrafast laser ablation mechanisms are reviewed first, with comparison to long pulse ablation characteristics. Next, some specific examples of applications in electronics and microelectronics industries are presented to emphasize the unique advantages of ultrafast lasers. Finally, the status of ultrafast laser sources as enabling tools is summarized.

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The development of ultrafast laser technologies within the last years created new perspectives, leading to the realization of new technologies and applications. In the automotive and mechanical industry the need for precision and high efficiency in a variety of applications make the ultrafast laser pulses an invaluable tool. Each of the studies presented in this review demonstrates the benefits of ultrafast laser pulses in industrial applications such as micro drilling of injection nozzles, lubrication reservoirs in laser honing and roll texturing.

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Ultra-short pulse laser light sources have been used for scientifi c research for more than two decade. In spite of this fact, these light sources are not utilized for industrial application. This is because an old type of ones has instability, large foot print and higher price. Recently, various lasing medium, the type of lasing medium, stable oscillator and the way of mode locking enable to make not only ultra-short pulses stable, but a size of light sources compact and a price reasonable. In this paper, current status of industrial ultra-short pulse laser light source is introduced.

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Laser direct machining has much attractive potential beyond traditional mechanical machining. We have been developing a micro-pattern fabrication system using an ultra-short pulse laser and are adapting this it to a large area with our high precision mechanical system. Our system is composed of a 1-axis highly accurate laser scan unit, a high precision positioning XY table, and a laser-machine synchronized controller. We realized a scanning system in a 120-mm scanning line, where the laser-focused points line up within error of 2-μm. In our spherical, 50-μm diameter, 25-μm deep sample, we realized formerror under ± 2-μm. With a high-speed scanning system, about 240-ms is required to make one shape. This means it takes a month to process a A4 size mold. Therefore, our next development target is a process that is five times faster.

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3D optical storage technology to record digital data with a femtosecond laser and read with a microscope inside fused silica. The recorded sample has a high thermostability (> 1000 ℃) and indicates semipermanent preservation of valuable information such as a cultural heritage. Unexpected periodic nanostructures beyond the diffraction limit of light are also observed in recorded sample. Such selfassembled nanostructures produced by femtosecond laser direct-writing in fused silica and nonreciprocal modifi cation originated from the anisotropic thermalization by the pulse-front-tilt are also reported.

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An interference pattern of ultra-short pulse laser can be transcribed to material surface, and great number of unit structures in matrix can be generated. In this paper, a variety of unit patterns are summarized in the case of four and six beam correlation. The patterns can be controlled by phase and amplitude variation between beams, and with ratio between processing fl uence and ablation threshold. In addition, interference patterns with concurrent irradiation of fundamental and second-harmonic generation (SHG), named “mode-locked interference” are shown. “Au nanowhisker”, which is a 3D nanostructure fabricated by SLS (Solid-Liquid-Solid) process induced by interfering femtosecond laser processing, was observed by TEM (transmission electron microscope).

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Using a pump-probe technique, we measured the refl ectivity of crystalline silicon to understand dynamic processes responsible for the periodic surface nanostructure formation with superimposed multiple shots of low-fl uence femtosecond (fs) laser pulses. The free-electron density and the lattice temperature on the surface were derived from the observed time-dependent refl ectivity change. The results have shown that the multiple low-fl uence fs laser pulses are crucial for the nanostructure formation through nonthermal interaction processes.

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Line-shaped femtosecond pulse is well suitable for large-area machining that requires a high-speed fabrication, for example, laser cutting, peeling and grooving. In this study, we demonstrate a shingleshot fabrication of three-dimensional line structure inside a glass, a laser peeling of indium tin oxide fi lm and a laser grooving of stainless with the line-shaped pulses by a diffractive cylindrical lens on a spatial light modulator.

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The irradiation of a focused femtosecond (fs) laser pulse modifi es silica glass to a chemically susceptible state in the vicinity of the focus. Using fs laser modification along a line and successive chemical etching, a microchannel can be fabricated. The present study investigated the dependence of the etching rate on the etching temperature for both modifi ed and un-modifi ed regions. The etching rates in both regions increased with increasing temperature, and the same activation energy of approximately 0.85 eV was determined in both regions. This result implies that high-speed etching can be achieved without loss of selectivity by increasing the etching temperature. Possible advantages and disadvantages of hightemperature etching are discussed.

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We investigated the ultraviolet laser-induced degradation of a nonlinear optical crystal CsLiB6O10 (CLBO). High-repetition-rate 266 nm pulses induced degradation of CLBO at a lower peak power density than the bulk laser-induced damage threshold. This research reveals that the degradation is caused by light-induced refractive index change observed as light-induced lensing effect in LiNbO3. We experimentally estimated the threshold intensity of this degradation. Al-doped CLBO samples have about two times higher threshold (40-50 MW/cm2) than conventional undoped samples (20-30 MW/cm2). We have established growth conditions to obtain high-quality CLBO crystals with lower light scattering. This high-quality crystal can effectively slow down the degradation.

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A high performance Cavity Ring-Down Spectroscopy (CRDS) system has been developed for measurements of atmospheric NO2 and H2CO. Combination of a frequency doubled tunable dye laser pumped by a high sampling rate A/D system enabled accumulation of 10000 shots of ring-down signal every 4 seconds. The A/D system sampling rate is 100 MS/s and the vertical resolution is 16 bit. The instrument was successfully applied to measure ambient NO2 in sub-urban Tokyo. Comparison with a commercial NOx box demonstrates the capability of this instrument.

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We propose a new wavefront control technique using a spatial light modulator (SLM) and a beam homogenizer. In a conventional tandem-type homogenizer, the first compensation plate converts a Gaussian beam to a flattop beam, and the second compensation plate corrects the distorted wavefront to a planar wavefront. In contrast, our method uses only the first plate and utilizes the wavefront generated by the first plate as a phase pattern for correction of a specific amount of spherical aberration (SA). Then, flexible SA correction becomes possible by placing an SLM at the position of the second plate. We applied this technique to internal laser processing of sapphire crystals. In the experiments, SA was generated due to the refractive index mismatch, deteriorating the laser processing performance. We confirmed that the beams had top-hat shapes and that the SA was well corrected with the proposed method.

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Precision machining industry requires practical technology for non-thermal processing. Using green ps laser pulses, we examined periodical micro-fabrication on the Cu plate surface. The diameter of the formed dimple was about 35 μm and around 10 μm depth. We observed no remarkable heat damage, such as discoloration, melting, or re-solidifi cation. The dispersion of the processing size was reduced by avoiding thermal damage. We achieved a processing amount of about 300 dimple/s.

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Various types of lasers have come into wide use in the industry, educational organizations and even citizens. The safe use of lasers is quite important for the persons relating with lasers. The rules and regulations for the safe use of lasers are shortly introduced. Several examples of ideas and devices to bring safety are also introduced.

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