Therapeutic applications of lasers have been mainly concentrated to destruct biological tissues by high laser energy. However, recently biostimulations by use of low laser energy become one of the recent topics in laser medicine. Furthermore, new lasers of diode, excimer, etc. are applying into medical fields and the special laser hospital was constructed and opened in Japan.

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The laser light is characterized by its monochromaticity, high spatial coherence and high energy. Basic techniques of using laser light and their applications in medical field are reviewed.

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For five years, we have been using soft laser irradiation to treat pain. Recently, we have found that lowenergy laser is effective for keloids, vitiligo, nevus spilus and skin shrinkage as well. Laser irradiation seems to normalize the metabolism (hyper, for keloids and nevus spilus; hypo, for vitiligo and shrinkage). Dr. Inada suggested that the above form of therapy was “zero entropic.” We would appreciate a longer explanation at some later date. This diode laser is extremely small, and in the future we expect even a small model, perhaps even a “powder laser” that can be injected into the bloodstream. This may cause a revolution in medicine.

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The following is an appraisal of the current application of laser technology in our special field from the standpoint of the gastrointestinal surgeon, with a presentation of the associated problem areas. In the field of oncology, in particular, it is our dream to achieve nonoperative therapy through the use of laser beams in cases that have traditionally required laparotomy. At present, nonoperative treatment has also become possible for some cases of early cancer. In concrete terms, however, there is the question of to the problems resulting from the currently applied methods of laser therapy.
The basic question is whether these problems have already brought laser treatment to its limits. What are the possibilities technology will offer in the future to resolve these problems? We hope that the presentation of these problems from the viewpoint of the clinician will provide a concrete clue to the development laser medicine.

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Laser technology in clinical medicine, such as surgery, diagnostic procedure and laboratory examination, is advancing at a rapid rate during the past decade.
With increasing knowledge and development of device, it can be reasonably expected that the multidisciplinary and multispeciality application of various kinds of laser will much increase in the future. With the growing respects of interfacing lasers with computers, the new advanced laser system will be developed in automated and selfcontrolled surgery, including local hyperthermia and endoscopy works.
Additionally, the delivery systems of getting the laser with a low power energy to the subjects will be improved successfully in psychosomatic medicine, rehabilitation and health medicine in Otolaryngological field.

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It has been said that singlet oxygen (¹O₂) has an important role on killing tumor cells in the photodynamic therapy using laser and hematoporyphyrin (Hp) or hematoporphyrin derivative (HpD). To evaluate the effect of the rate equation of ¹O₂ during the photodynamic reaction, the lifetime of excited triplet state of Hp was determined using CCl₄, C₂ H₅OH and water as the solvent. The rate equation of ¹O₂ was very low due to the short lifetime of excited triplet state of Hp. Those was 480ns in CCl₄, 280ns in C₂H₅OH and unmeasurable in water. It was suggested that the lifetime of excited triplet state of Hp was based on dye triplet-triplet absorption induced by Nd-YAG or N₂ dye laser, and the difference in the lifetime was due to the radiationless energy transfer rate of the solvent by molecular vibration.
Additionally, the optical density of Hp was determined in various concentration under O₂ bubbling using the solvents described above. The increased absorption was found at 502nm under O₂ bubbling, and the increased optical density was correlated with the O₂ and Hp concentrations. The energy level in wave length of 502nm was thought to be the sum of the energy levels of O₂ and of excited triplet state of Hp. These results suggest that the increased absorption was produced by “cooperative absorption” of Hp-O₂ complex.
Thus the elevation of the rate equation of ¹O₂ by the irradiation of a specific wave length of laser under high concentration of O₂ circumstance will improve the efficiency of the photodynamic therapy on cancer.

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