Many kinds of lasers in the ultraviolet to the mid-infrared range have already become widespread treatment devices in medical fi elds. A variety of laser-tissue interactions are produced when laser beams are applied to biomolecules and biological tissues. Laser-tissue interactions strongly depend on optical properties. Realizing safe and effective laser treatments requires comprehensive knowledge of lasertissue interactions. This paper reviews the absorption properties of biomolecules, biological tissues, and laser-tissue interactions and introduces the domestic trends of lasers in surgery and medicine with approved devices.

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Photodynamic therapy (PDT) using 664-nm laser diode and talaporfi n sodium has been developed in Japan as promising therapeutic technology. It has deeper light penetration and lower photosensitivity risk than conventional PDT. In this article, we reviewed the development history of PDT in clinical practice and irradiation technology, and summarized the latest development of talaporfi n sodium mediated PDT for malignant brain tumor and local failure esophageal cancer after chemoradiotherapy or radiotherapy.

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Endovenous laser ablation (EVLA) is now being accepted as one of the most effi cacious treatment of varicose vein. As diode laser device for varicose vein treatment, we have today on the medical device market, ELVeS laser and ELVeS laser 1470 both handled by Integral Corporation with manufacturing and marketing approval following Japanese pharmaceutical regulations. These two devices are widely used in Japanese medical clinic and hospitals. Main difference between these two devices are derived from wave length of laser and fi ber.

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We have been developing high-power electrical supply units for high-power gas and solid lasers for many years. Recently, we have also been developing a high performance power supply unit for semiconductor lasers. We have also developed a medical therapy device for pain relaxation and commercialized it using such experienced technologies of semiconductor laser power supply. We describe the development and approval processes of the medical therapy device and disclose the effect of a semiconductor laser device on pain relaxation.

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The author will summarize the development of pulsed laser-induced liquid jet surgery system, which facilitates to achieve both maximal resection of the lesion and maximal preservation of the function after the surgery. This technology discriminates from other in terms of no heat damage, tissue selectivity, and high affi nity to be incorporated into minimally invasive medical device, such as catheter and endoscopy. The device is now in the phase of clinical study for microsurgery, but had three major barriers during this translational research process. The fi rst barrier being technological issue （how to generate high speed small pulsed water jet）, the second being regulatory and IP issues, and the third being business issues（ how to increase the market size to facilitate working with the industries for commercialization of the device）. We would like to emphasize the importance of restructuring the team in terms of exit strategy once feasibility have been proved.

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The authors have developed new non-thermal catheter ablation for a tachyarrhythmia treatment using an extracellular photosensitization reaction. The currently-used catheter ablation treatments have severe complications caused mainly by heat. The authors proposed the use of photosensitization reaction with excitation laser irradiation shortly after a photosensitizer injection; PD Ablation®. The PD Ablation® archives immediate electrical conduction block that is needed in tachyarrhythmia by membrane damage from the outside the cell. The authors have investigated the fundamental mechanism and demonstrated the electrical conduction blockade performance using animal models. The authors have also developed a laser catheter containing a diffuse plastic optical fi ber. The PD Ablation would be evaluated to have plural great merits over the world’s new devices for tachyarrhythmia ablation. The authors forward the research and development in cooperation with medical department and several enterprises with a university venture as a principal.

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We report the current status of the less-invasive laser treatment of atherosclerosis with a 5.75-μm Wavelength. This selective treatment exploits characteristic absorption by biomolecules in the midinfrared range. With pulsed lasers, we achieved the selective removal of atherosclerotic plaque at 5.75 μm, which is the absorption peak of cholesteryl esters in atherosclerotic plaque. The absorption is derived from the C = O stretching vibration mode. This result demonstrated the effectiveness of the midinfrared region for advanced less-invasive treatments. However, for clinical applications, problems remain, such as the equipment size, ablation efficiency, and the thermal effect. Therefore, further progress of mid-infrared light sources is required.

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Pharmaceuticals and Medical Devices Agency (PMDA), which reviews high-risk medical devices, summarizes new guidelines about medical lasers through discussions with academia and industry. The guidelines offer basic concepts about the evaluations of medical lasers that are not limited to laser scalpels. PMDA believes that this activity promotes novel medical laser development. This article introduces the contents of recent PMDA activity and new basic thoughts about medical lasers.

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Less-invasive methods are required for caries treatment. Our previous study achieved the selective removal of demineralized dentin by the irradiation of a nanosecond-pulsed laser at wavelengths of around 6 μm, which are the absorption wavelengths of organic materials, without water spray. Absorption bands also originated from the organic materials at around 3 μm. This study investigated the ablation property by a nanosecond-pulsed laser at a wavelength of 2.94 μm without water spray. We also compared our new laser method with a conventional Er:YAG laser. As a result, the selective removal of demineralized dentin was observed by both lasers, and the thermal effect by nanosecond-pulsed-laser irradiation was less than that of the Er:YAG laser. We believe that a nanosecond-pulsed laser at a wavelength of 2.94 μm is effective for the selective removal of carious dentin.

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We compared the effi cacies of photodynamic therapy (PDT) with a light-emitting diode (LED) at the green or red wavelength region using a computational simulation model with the Monte Carlo method and a theoretical estimation based on quantum chemistry. The amount of singlet oxygen produced by a green or red LED was comparable with that produced by a green or red laser, respectively, and that produced by the green LED with a peak emission wavelength of 515 nm exceeded that produced by the red LED with a peak emission wavelength of 629 nm within a depth of about 2 mm. We infer that PDT with a green LED is effective for cancers localized around such tissue surfaces as the intraepithelial carcinoma of the bladder.

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We have been developing a new laser annealing technology with a micro lens array (MLA). In this technology, an Nd: YAG laser is irradiated onto a specifi c local area using MLA that only targets the channel area of the thin-fi lm transistor (TFT) inside sub pixels on a TFT backplane substrate for fl at panel displays. However, due to the high coherency of Nd: YAG lasers, illuminating MLA at good uniformity is diffi cult by standard illumination optics. Therefore, we developed a new laser scramble unit that spatially shifts the laser beam at high speeds to reduce the illumination MURA caused by interference fringes. Using this laser scramble unit, we illuminated MLA and only annealed a-Si fi lm on the channel region of the simple TFT structure at good uniformity. We also confi rmed improvement in the electron mobility of the TFT annealed by this laser irradiation system.

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Silica toroid microcavities is an ideal platform if we want to obtain high sensitivity and small device size simultaneously. However, it requires precise alignment of a tapered optical fi ber in order to couple light into the microcavity. In this study we report on the packaging of a silica toroidal microcavity with an input-output tapered optical fi ber, which enable us to make this device portable and use for practical applications. The obtained Q of the packaged device is 1.7×106, and we performed thermal sensing by using this device.

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In high-resolution molecular spectroscopy, precise measurements of the optical frequency are crucial to evaluate minute shifts and splittings of the energy levels. In this study, we developed a frequency measurement system of cw lasers scanning the wide range employing an optical frequency comb. We demonstrated the frequency measurement of a scanning dye laser, and analyzed the spectral characteristics during the laser scan. The developed system was applied to Doppler-free two-photon absorption spectroscopy of S1 1B1u(v4 = 1)←S0 1Ag(v = 0) transition of naphthalene. We obtained wellresolved rovibronic spectra with the linewidth of 2.48 MHz, and determined absolute frequencies with the uncertainty of several tens of kHz. For the Q(K)Q(J) transitions, the rotational lines were assigned, and molecular constants in the excited state were determined.

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