A measurement system for ultrafast time-resolved fluorescence spectroscopy was constructed based on electronic Kerr effect. Suitable Kerr medium was searched among glasses and isotropic single crystals by using the Z-scan method that can evaluate two-photon absorption coefficient and photo-induced refractive index change. With optimization of design of the optical system, we achieved the time resolution of 180 femto-second, 5 % gating transmittance and the one-order-faster data acquisition than conventional method. Time-resolved spectra were measured for photoactive yellow protein (PYP). The Kerr-gating system enabled for the first time to obtain the 2-dimensional, time-wavelength mapping of time-resolved fluorescence spectra in the femto-pico-second time region. Vibrating behavior of fluorescence intensity peak was clearly recognized, which is curious and has never seen in dye solution systems at room temperature. It suggests that, in PYP, chromophore is energetically isolated from the main structure of amino-acid chain and that photo-excited energy is dissipates through specific channels.

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We investigated an effect of short pulse laser irradiation on protein crystallization in supersaturated solution. Effective crystallization of a protein molecule was confirmed by applying a femtosecond laser. We call this process laser irradiated growth technique (LIGHT). Protein crystals were obtained by LIGHT from normally uncrystallized conditions. Experimental results indicate that protein nucleation depends on the laser-irradiated conditions, and thus we must optimize the laser condition to obtain high-quality protein crystals. The crystallization will be promoted by nonlinear phenomena of the femtosecond laser. However, the mechanism is not clear. The challenge is to investigate what really happened.

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Cypoviruses are insect viruses that produce a form of progeny in which virions are embedded within a crystalline particle called the polyhedron. In this study, we demonstrated that the N-terminus, but not the C-terminus of the virion structural protein, VP3, functions as an "occlusion signal", which can direct the stable incorporation of foreign proteins into polyhedra. A VP3-EGFP fusion protein was shown to be uniformly occluded within the polyhedra, to be detectable at the surface of these particles. A broader survey revealed that the VP3 occlusion signal could direct the incorporation of foreign proteins into polyhedra. Immune reactivity were detected on the surface of polyhedra containing occluded foreign proteins, when these particles were arrayed on a glass slide by laser fabrication.

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A shockwave induced by focusing an intense femtosecond laser on a culture medium under a microscope was applied to manipulate single bio-cell. Propagation dynamics of the shockwave was investigated by observing the motions of polymer microspheres floating in the culture medium and the force exerted to microspheres by the shockwave was estimated to be in the order of nN. This is over 1000 times larger than that of photon force due to conventional laser trapping and strong enough to manipulate μm-sized biological cells. As a representative application of the method, it was demonstrated that a single animal cell cultured on a plastic substrate was separated individually from the substrate by the shockwave. On the basis of these results, we discuss here a possibility of individual manipulation of adhesive cells.

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In addition to infectious diseases, life-style related diseases become a more common reason for medication of elderly people than ever. Dysfunction of organs is an underlying cause of these diseases. Progressive aging of society urges us to find cures for this type of diseases. Taking advantage of versatile differentiation potentials in stem cells, researchers are attempting a functional restoration of damaged tissues and/or organs. Laser technology has provided such a powerful tool for the study of hematopoietic stem cells at a single-cell level as fluorescence activated cell sorter (FACS). However, many unanswered questions remain for understanding how growth and differentiation of stem cells are regulated and can be manipulated. Taking cartilage formation and repair by mesenchymal stem cells as a model, we explore possible applications of laser technology for the study of tissue stem cells at a single-cell level.

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We report fabrication of three-dimensional (3-D) microchannels inside transparent materials. The 3-D microfabrication was achieved by two steps. First, femtosecond pulses were focussed into the transparent materials, and continuous spots of 3-D micro modification were made. The modified spots were made along with a programmed pattern by scanning the sample. Next, the materials were immersed in aqueous solution of HF-based etchant. The difference in etching rate between raw- and modified-regions results in the 3-D microchannel. By this method, 3-D microchannels were fabricated in the materials without special photo-sensitivity such as silica glass and sapphire. In addition, one-step fabrication (without etching) was achieved in a polymer material of PMMA.

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Using the ArF excimer laser to alter corneal tissue is now applicable to the field of ophthalmology. For the treatment of corneal scarring or corneal dystrophy, phototherapeutic keratectomy (PTK) may be performed, and photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) is useful to treat refractive errors such as myopia, hyperopia, or astigmatism. A videokeratoscope and wavefront sensor are useful for the evaluation of corneal topography and the quality of vision following refractive surgery.

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Low frequency vibrations of the native PYP and related systems in solution have been investigated in "time" (fs fluorescence up-conversion) and "frequency" (resonance Raman) domains to elucidate their role in ultrafast photoisomerization reaction dynamics of PYP. Tentative assignments of the oscillatory components to particular vibrations are proposed supported by normal mode calculations based on DFT and ab initio MO methods. It is concluded that the out-of-plane skeleton bending mode of the chromophore, γ₁₆, is responsible for the observed oscillations in native and all mutant PYPs (f₁ ∼ 135 cm^-1), while in-plane ν'₄₂ and ν'₄₃ modes are probably responsible for oscillations observed in the PYP analogue with locked chromophore. A dynamic model called "trigger mode mediated guidance" has been proposed to explain in simple terms the ultrafast primary process initiating PYP's photocycle. Furthermore, first successful fluorescence dynamics experiments on PYP single crystals with femtosecond time resolution are presented and discussed.

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The micromachining of hydroxyapatite (HAp) and collagen is highly required for orthopedics and dentistry, because human bone and tooth consist mainly of HAp oriented along the collagen. We have evaluated ultrashort Ti:sapphire laser ablation of HAp and collagen with pulsewidth of 50 fs - 2 ps at 820 nm and 1 kpps. The crucial medical issue is to preserve the chemical property of the ablated surface. If chemical properties of HAp and collagen change once, the human bone or tooth cannot re-grow after laser processing. Using x-ray photoelectron spectroscopy we have observed chemical properties of the HAp ablated in air. As a result it is found that the ablated surface is unchanged after laser ablation over the pulsewidth range used in this experiment. Human tooth enamel is precisely ablated with 60 fs and 2 ps laser pulses. Collagen is also found to preserve the initial infrared properties during 160 fs laser ablation.

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The bonding between a metal surface of a human joint prosthesis and a bone is not perfect. It makes the loosening of a metal component from a bone. Porous coating method is widely used to have a rough metal surface, but it cannot regulate the shape of a metal surface. It cannot make enough bonding. Our method is a new metal processing method using a laser scanning for a joint prosthesis, which was developed in Osaka Univ. Graduate School. The metal surface with a microscopic canal structure, which was processed by a new method, has a few times bonding strength compared to a porous coated surface. A new bone invasion was observed in all cavities of the canals. The results encourage the development of a new joint prosthesis which has no loosening from a bone.

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The Bessel beam (J₀ beam) has potential for use in laser micro fabrication. We analyzed numerically the characteristics of a J₀ beam at different distances between the optical axes of the Axicon and the source beam. When both optical axes are parallel, the generated J₀ beam propagates along the optical axis of the Axicon. In the case of a top-hat source beam, both maximum intensity on the propagation axis and its propagation distance decrease with increasing distance between the optical axes. In the case of a Gaussian source beam, however, the ideal J₀ beam characteristic is maintained almost completely, provided the distance between the optical axes is short.

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