Minoru Obara

Temperature measurement for energy-efficient ablation by thermal radiation with a microsecond time constant from the corneal surface during ArF excimer laser ablation.

Measurement of the temperature of the corneal surface during photorefractive keratectomy (PRK) is thought to be useful for monitoring the corneal ablation process, since the photothermal process has been proposed as the major mechanism of ArF excimer laser ablation. For temperature measurement, we measured thermal radiation from the corneal surface during ArF excimer laser ablation using a mercury-cadmium-telluride detector with a 1-micros time constant. To investigate the effects of temperature on ablation depth, the ablation depth of the cornea was measured by microscopy. When corneal ablation was initiated at the fluence of 65 mJ/cm2, the corneal surface temperature rose to 60-70 degrees C. The energy required for a unit-depth ablation (degrees C/microm) was lowest at 120 micro C. Monitoring of transient temperature during PRK provides important information on energy-efficient ablation, which may enable rapid and safe corneal incisions.

Gain and discharge characteristics of electron‐beam switched KrF lasers

Although small-signal gain measurements of rare-gas halide lasers were recently carried out only for direct electron-beam-pumped and self-sustained-discharge pumped lasers, there is no report on the gain measurement of the electron-beam-switched-discharge KrF laser. Electron-beam switched discharge pumped KrF lasers were studied to obtain detailed experimental data on the relationship between the discharge stability and the small-signal gain coefficient g/sub o/. As a result, a high gain coefficient g/sub o/ in excess of 11%/cm was obtained and the relationship between the discharge stability and the small-signal gain coefficient was clarified. The electron-beam-switched-discharge pumping which needs no gap switches in the discharge circuit is especially suitable for high-rep.-rated rare-gas halide lasers.

Gene delivery to skin with laser-induced stress wave

We investigated gene delivery by laser-induced stress waves (LISWs) generated by irradiating a solid target with nanosecond laser pulses. Highly efficient and site-specific gene transfer has been achieved by applying a few pulses of LISWs.

Development of a stable, high-repetition rate, 1W femtosecond regenerative amplifier system for biomedical applications

We have developed a high-repetition, 1-W, and 70 fs regenerative amplifier system. The stable operation was obtained due to a seeding fiber laser, a compact folded cavity, and a green pump source built by ourselves.

Transdermal delivery of photosensitizer by laser-induced stress wave

The skin permeability of most of drugs is low, because the stratum corneum works as a solid barrier. It is required, therefore, to enhance the skin permeability for transdermal delivery of drug. To investigate the effects of heating skin and exposing skin to a laser-induced stress wave (LISW) on the drug permeability, we tried to deliver porfimer sodium into rat’s skin. The experiment was performed under the four different skin conditions; exposing to a LISW (case 1); heating (case 2); exposing to a LISW and heating (case 3); control (case 4). It was observed in all cases except the case 4 (control), the drug permeated into the dermis through the epidermis. The deepest penetration was obtained in the case 3 (a LISW plus heating). It was suggested that heating increased the fluidity of the lipid bilayers in the stratum corneum, and therefore the drug permeability might be enhanced.

The novel variable function laser surgical system using mid-IR cascade oscillation fiber laser with Ho/sup 3+/ ion: tissue interaction and system construction

Summary form only given, as follows. We demonstrated function variability to living soft tissue of the mid-IR cascade oscillation Ho/sup 3+/ fiber laser at 3 μm and 2 μm operation of continuous wave radiation for surgical applications. Our study was both experimental and theoretical.

Fiber-optic viscoelasticity measurement system for embryo: gelatin model experiment

We studied a fiber-optic dynamic viscoelasticity measurement system to develop a noninvasive measurement for human embryo viability. We obtained the dynamic viscoelasticity of a gelatin gel model (1/spl times/1/spl times/1 cm) by optical displacement monitoring, stress and phase difference monitoring. In our preliminary system, we employed the combination of noninvasive optical displacement measurement and contact vibrational addition to the sample. Fiber-optic reflectometry of a He-Ne laser through a thin fiber was used. We obtained the linear relation between the estimated dynamic viscoelasticity and gelatin concentration to be from 3.75 to 7.5%. Moreover, this estimated dynamic viscoelasticity coincided with the reported value. These results indicated the possibility of noncontact and noninvasive effective evaluation for embryo viability.

Temperature measurements by thermal radiation during ArF excimer laser ablation with gelatin gel

We measured temperature elevation during photorefractive keratectomy (PRK) by thermal radiation. The thermal radiation from ablating surface of gelatin gel (15%wt) by ArF excimer laser was detected by a MCT detector with 1 /spl mu/s rise time. The measured signal increased sharply just after the laser pulse and decreased quasi-exponentially. We calculated the temperature elevation using Stefan-Boltzmann radiation law. The maximum temperature elevation was 97/spl deg/C at 208 mJ/cm/sup 2/ in laser fluence. The temperature elevation over 60/spl deg/C was kept for 85 /spl mu/s. These temperature elevation might induce possible heat damage on ablated surface. Our high temporal resolution temperature monitoring may be available to achieve safety and precise PRK.

Signal analysis of fiber optic probe method from Ho:YAG laser ablation bubble

We experimentally and theoretically studied interpretation of the waveform signal which was obtained by the fiber-optic probe method during Ho:YAG laser ablation. We monitored behavior of the ablation bubble which occurs at the fiber tip during the ablation by means of developed fiber-optic probe method as well as time-resolved photography to investigate the information which involves the waveform signal. We used water and agar as model materials for different purposes. We determined that the waveform signal from the fiber-optic probe method is mainly attributed to the reflection of the boundary between the water-vapor bubble and surrounding material/tissue. We also found that the intensive shockwave which is induced may be monitored by our method.