Yuichi Hashishin

Microstructures of ultralow-density foam plastics obtained by altering the coagulant alcohol

The present report describes ultralow density (2–12 mg/cm3) plastic (CH2) foams whose density is close to the cutoff density of the plasma for visible and near-infrared light beams (0.55–1.3 µm). These foams are prepared from a poly(4-methyl-1-pentene) gel with hexanol derivatives by extraction using supercritical fluid CO2. Their intended use is in laser-plasma experiments and as a laser-plasma X-ray source. Their microstructure (2–10 µm) was finer than that of the previous poly(4-methyl-1-pentene) foam and could be varied using different hexanols.

Optical Beam Guides For Medical CO 2 And Excimer Lasers

The metal and polymer compound hollow tube is effective guide for cw CO2laser beam transmission. We have tride to high peak pulse CO2laser beam delivery with the hollow tube guide. Using the CO2 pulse laser have high peak (46MW max. ,short pulse width(80ns) and repeat pulses(under lOpps). In this experiments, the laser beam transmittance was obtained ca.90%/m. So the hollow tube are confirmed as useful beam guide technique for also pulse CO2 laser. We are having also investigates of UV laser beam transmission with the hollow tube as CO2 laser beam. We have used KrF excimer laser(248nm wavelength). We found that the random polarized beam transmittance was ca.26%/m, if polarized beam was ca.37%/m, delivery average power and energy were ca.1 watt(220kW peak power) and 5m.J. per pulse respectively. On the other hand, we have been developing UV optical fiber for Kr F laser, Results so far were obtained above 80%/m transmittance by OH ion added quartz glass fiber.

Observation of Dynamic Absorption Properties of Wet Gelatin around λ=6.05 µm Using a Mid-Infrared Free Electron Laser

It is essential for soft tissue cutting to precisely predict the effects of laser irradiation before treatment. The purpose of the present study was to investigate the dynamic absorption coefficients of wet gelatin around λ=6.05 µm (tuned to the OH bending and amide-I bands) during laser irradiation. Wet gelatin was irradiated by a tunable mid-infrared free electron laser within the wavelength range of 5.6–6.7 µm. The incident fluence was fixed at 3.6±0.3 J/cm2. Structural changes of the irradiated gelatin were observed with an optical microscope. At λ=6.05 µm, the wet gelatin was efficiently removed due to vaporization of water, and the absorption coefficient during irradiation increased slightly by 30–40% of magnitude from that before irradiation. Thus, we showed the possibility that 6.05-µm-light can predictably remove soft tissue without unexpected effects. A laser system with λ=6.05 µm is expected to be a novel cutaneous laser.

Real-time monitoring of the surface modification of root dentin using photoacoustic spectroscopy and photothermal radiometry

For non-invasive laser dental treatmet, a real-time and non-contact monitoring technique is needed. We have investigated the extent of the surface modification of root dentin using photoacoustic spectroscopy (PAS) and pulsed-photothermal radiometry (PPTR), and have discussed the applicability of each technology to in vivo monitoring during laser treatment. Root dentins were used as specimens. The wavelength, average power density, and exposure time used were varied within the ranges λ = 9.0-10.6 μm, Pav = 7-28 W/cm2, and τ = 0-10 s respectively. The temporal behaviors of the laser-induced acoustic waves and the temperature rise were measured with an audible microphone and a radiation thermometer, respectively. The extent of the surface modification was evaluated by using information on the ablation depth and the absorption spectrum of the irradiated dentin. The morphological and chemical changes of the irradiated dentin can be made available to assist in dentinal tubule sealing and increased acid resistance for root surface caries therapy. It was found that time-resolved measurements of the acoustic waves and the temperature are useful for a real-time understanding of the extent of the morphological and chemical changes, respectively. We have demonstrated that applicability of an in vivo monitoring technique using PAS and PPTR for root surface caries therapy.

UV-laser/biotissue interactions and delivery systems

The interactions of UV laser beams and biotissues have been studied. The cutting quality of an ArF laser was the best sharp for hard biotissues (e.g. a bone, a tooth). From the current experiments, we found that the KrF laser beam has the highest incision ability for biological lipid of excimer lasers. For example, suet was cut off sharply by the KrF laser beam. On the other hand, the ArF laser incision has no thermal damage on suet even for the high repetition rate and the high energy fluence. However the conventional optical quartz fiber can not be available for an excimer laser beam (far-UV). So we have been investigating about UV laser power beam delivery systems. In the case of the hollow light guide with the aluminum-phosphor bronze reflector, we have obtained 56 and 75%/m transmittance of the ArF and KrF laser in straight state, respectively. Its delivery energy was 45 and 110 mJ/pulse of the ArF and KrF laser, respectively. The ArF laser transmittance has been tried in various atmosphere such as air, nitrogen, oxygen and helium. Finally, the medium of the laser delivery of the hollow light guide had better use the helium gas instead of the air. And the ArF laser transmittance and delivery energy were obtained 71%/m and 50 mJ/pulse, respectively. We have also tried the quartz fiber with OH ion doped core. The effects of a lightly doped clad with B and F on the transmittance have been investigated. In the one pulse operation, the ArF laser transmittance of B and F doped clad fiber was obtained 82%/m, which was better than that of only F doped clad fiber. The hollow light guide is suitable for the delivery system of UV laser scalpels, and the UV fiber is the useful delivery system of UV laser endoscopes.

Excimer laser beam delivery systems for medical applications

We have been doing the basic experiments of UV laser beams and biotissue interaction with both KrF and XeCl lasers. However, the conventional optical fiber can not be available for power UV beams. So we have been investigating about UV power beam delivery systems. These experiments carry on with the same elements doped quartz fibers and the hollow tube. The doped elements are OH ion, chlorine and fluorine. In our latest work, we have tried ArF excimer laser and biotissue interactions, and the beam delivery experiments. From our experimental results, we found that the ArF laser beam has high incision ability for hard biotissue. For example, in the case of the cows bone incision, the incision depth by ArF laser was ca.15 times of KrF laser. Therefore, ArF laser would be expected to harden biotissue therapy as non-thermal method. However, its beam delivery is difficult to work in this time. We will develop ArF laser beam delivery systems.

Development of optical fiber for medical Er:YAG laser

The Er:YAG laser beam has stronger absorbability by water than the CO2 laser beam. Therefore, the Er:YAG laser is expected to be used as the surgical treatment beam for water- rich biotissue. And if the effective optical fiber of 3 micrometers band is developed, it is also expected for use as an endoscopic beam. So we are doing investigations of the optical fiber for Er:YAG laser. The optical fibers used are fluoride glass, chalcogenide glass fibers, and the hollow tube guide. From our experimental results, these Er:YAG laser beam delivery techniques would be expected to perform well in practical use.

Infrared delivery systems for Er:YAG laser

Er:YAG laser beams (2.94 micrometers ) have more strong absorbability by water than CO2 laser beams (10.6 micrometers ). Er:Yag lasers are expected as a treatment beam for water rich biotissue, we considered the application of Er:YAG lasers for medical use in the near future. When applying it for medical use, the delivery systems must be prepared. So we are investigating higher pulse power Er:YAG laser beam transmission with fluoride glass fibers, chalcogenide glass fibers, and hollow tube guides. From our experimental results, these beam delivery techniques are possible for Er:YAG lasers.

UV-Beam Guide For Medical Excimer Lasers

As is well known visible and near infrared beams are able to use ordinary quartz fiber. There are needed some technique about ultraviolet beams. We have been investigating about that, one of the technique is to OH on added to high purity quartz fiber. So in our laboratory, we have obtained 85%/m 248nm beam transmittance in over 200ppm 0 ion added quartz fiber at the milliwatt power regions. On the other hand, we have investigating 308nm beam delivery with the OH ion unadded high purity quartz fiber. The transmittance was over 85%/m , therefore the high purity quartz fiber is usable to XeC1 laser beam delivery systems,we have been investigating also UV-beam delivery with the metal-polymer compound he tube.

Hollow Light Guide Tube For CO2 Laser Beam

The suitable laser power light guide system is neccessary in the medical laser apparatus. In order that the function be must effective, enough flexibility and safety of power laser guide are required. We have developed a non-toxic flexible CO2 laser beam guide with metal and polymer hollow tube. The present experimental results show that the CO2 laser beam tran smission rate about 85% per meter, emitted power was obtained about 81W at 1 meter guide length and any accidents were not happen under the continuous transmission. The emitted light beam spot was focused to about 0.5mm diameter. We have obtained emission beam power density of 40kW/cm2. The amounts of this power density will be practical use for medical applications. The guide tube have flexibility,the tube is bent easily to a round shape at radius above 10cm. The twist of tube is also possible. On the other hand, in order to inprovement of flexibility, we have forward trial product of narrow tube. The hollow guide tube will anticipate development of new medical application of CO2 laser.