Katsumasa Iwai

Transmission characteristics of terahertz hollow fiber with an absorptive dielectric inner-coating film

We report calculation results for the transmission characteristics of terahertz hollow fibers with inner coatings of absorptive dielectric and metal layers. The absorption property of the dielectric film has an obvious influence on the transmission property of terahertz hollow fiber, because the optimum thickness of the dielectric layer is several tens of micrometers. Calculations were conducted on the loss properties of the hollow fiber with and without the absorptive dielectric layer. Important results were obtained, such as the optimum refractive index for the absorptive dielectric layer and the absorption tolerances for hollow fibers with various inner diameters.

Erbium:YAG laser lithotripsy by use of a flexible hollow waveguide with an end-scaling cap.

An Er:YAG laser light delivery system composed of a polymer-coated silver hollow waveguide and a quartz sealing cap has been developed for calculus fragmentation. Sealing caps with various distal-end geometries were fabricated, and the focusing effects of these caps for Er:YAG laser light were measured both in air and in water. Owing to the high power capability of the quartz a beam of sealing caps, Er:YAG laser light with an output energy of 200 mJ and a repetition rate of 10 Hz was successfully transmitted in saline solution by use of the system. Calculus fragmentation experiments conducted in vitro showed that the delivery system is suitable for medical applications in lithotripsy. We also found that the cap with a focusing effect is more effective in cutting calculi. The deterioration of the sealing caps after calculus fragmentation is also discussed.

Optical properties of AgI/Ag infrared hollow fiber in the visible wavelength region

We report on AgI/Ag infrared hollow fiber with low-loss in visible region. Improved methods of silver plating and iodination were proposed to fabricate the hollow fiber. The surface roughness of the silver layer and the silver iodide layer was reduced by the pretreatment with an SnCl2 solution and low iodination temperature. Losses for the Er:YAG and green laser light were 0.4 and 7dB/m. The loss property of green laser beam was low to deliver a pilot beam for the invisible infrared laser light. Owing to the smooth and uniform AgI film, the loss spectrum of the hollow fiber showed clear interference peaks in the visible region. An empirical formula for AgI material dispersion was derived, which is of special importance for the design of high-performance AgI/Ag hollow fiber.

Infrared hollow fiber with a vitreous film as the dielectric inner coating layer

A vitreous material with an optimum reflective index of 1.41 for dielectric metallic hollow fiber is used for what is believed to be the first time. A smooth vitreous film is formed by the treatment of a hardener at room temperature by using the liquid-phase coating technique. Low-loss properties were obtained in both the infrared and visible wavelength regions, and the fibers are of high durability when sterilized. This hollow fiber is promising for use in medical applications or other harsh environments.

Characteristics of calculus fragmentation with Er:YAG laser light emitted by an infrared hollow optical fiber with various sealing caps

We have experimentally quantified calculus fragmentation by Er:YAG laser light. Er:YAG laser light was delivered to an underwater target through a sealed hollow optical fiber. Fragmentation efficiency was obtained for an alumina ball used as a calculus model when sealing caps with various focusing effects were used. Three types of human calculus were analyzed, and their absorption properties at the wavelength of Er:YAG laser light were obtained. The relationships among the absorption properties, calculus constituents, and fragmentation efficiency are discussed.

Fabrication and transmission characteristics of infrared hollow fiber based on silver-clad stainless steel pipes

Silver-clad stainless steel pipe is used as the supporting tube for the fabrication of infrared hollow fiber. The hollow fiber has high mechanical strength and is highly durable for use in the medical sterilization process. Film of a cyclic olefin polymer layer or silver iodide (AgI) was coated internally to reduce the transmission loss. A liquid-filling method is proposed for coating the AgI layer. Multiple coating processes proved to be effective to increase the AgI film thickness. A treatment of sodium thiosulfate water solution is also proposed to reduce the film thickness. The film thickness can be accurately controlled by combining the coating and decoating techniques. A loss of less than 0.2 dB was obtained for CO2 laser light for a hollow pipe with a length of 280 mm and an inside diameter of 0.75 mm.

Hollow polycarbonate fiber for Er:YAG laser light delivery.

We developed hollow fibers with polycarbonate (PC) capillaries for use as a supporting tube. The PC capillaries were prepared by using a glass-drawing technique. Hollow PC fibers are safer and more flexible than hollow glass fibers because no fragments are released when the fibers are broken in various applications. Inner coating layers of silver and cyclic olefin polymer (COP) enhanced the reflection rate at the Er:YAG laser light wavelength. Using these fibers, we attained low loss for Er:YAG laser light transmission. By adjusting the drawing temperature in the fabrication of the PC capillaries, we created a smooth inner surface and uniform PC capillaries. We also demonstrated low-loss properties for visible pilot beams.

Fabrication and characterization of infrared hollow fiber with multi- SiO(2) and AgI inner-coating layers.

We report the transmission characteristics of infrared hollow fiber with multi- AgI and SiO(2) inner-coating layers in the mid-infrared region. A three-dielectric-layer hollow glass fiber with a SiO(2)-AgI-SiO(2)-Ag structure was fabricated and low-loss property was obtained in the mid-infrared region. The SiO(2) films were coated by use of the liquid-phase coating method and a semi-inorganic polymer was used as the coating material. For deposition of the AgI film between the two SiO(2) films, a silver film was first plated by use of the silver mirror reaction method. Then the iodination process was conducted to turn the silver layer into silver iodide. A calculation method was also developed to estimate the film thickness of dielectric layers in each fabrication step according to the position of loss peaks in the measured loss spectra. Good agreement between calculated and measured loss spectra was demonstrated by taking into consideration material dispersion and surface roughness of inner-coating films.

Synchronous radiation with Er:YAG and Ho:YAG lasers for efficient ablation of hard tissues

Er:YAG and Ho:YAG laser beams were combined to irradiate hard tissues to achieve highly efficient ablation with low laser power. The delay time between pulses of the two lasers was controlled to irradiate alumina ceramic balls used as hard tissue models. With optimized delay time, the combined laser beam perforated the sample 40% deeper than independent radiation by either an Er:YAG or Ho:YAG laser. An ultra-high-speed camera and an infrared thermography camera were used to observe and investigate the ablation mechanisms.

AgI-coated silver-clad stainless steel hollow waveguides for infrared lightwave transmission and their applications

We fabricated silver iodide (AgI)-coated silver hollow waveguides to transmit a wide range of infrared (IR) light. Silver-clad stainless steel pipes were used as a supporting pipe. Since this type of metallic hollow waveguide has high mechanical strength and heat resistance, it is suitable as a rigid lightwave probe for various applications such as dental or medical laser treatment, IR spectroscopy, thermal radiometry, and laser processing. Considering these applications, we estimated the hollow waveguides with different thicknesses of the AgI layer. By optimizing the AgI layer thickness according to the wavelength of propagating light, we succeeded in efficiently transmitting Er-YAG and CO(2) laser light. We also studied the optical characteristics of a wide range of incoherent light for IR spectroscopy and radiometry applications using these metallic hollow waveguides as lightwave probes.