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.

Optimal design for hollow fiber inner-coated by dielectric layers with surface roughness.

We report the optimal design for hollow fiber inner-coated with metallic and multidielectric layers by using ray-optics theory. Transmission characteristics of the multilayer hollow fiber are more dependent on the film surface roughness in the IR region. Comparisons of fibers with smooth and rough films are made and discussed in detail. The optimal design for film thickness, inner radius, and the number of layers and refractive indices is presented. The calculation results are important for structure design, material selection, and fabrication when considering imperfections in film-coating techniques. Multilayer fibers are fabricated based on the calculation and experimental results agree with the theoretical ones.

Ceramic bracket debonding by Tm:YAP laser irradiation.

OBJECTIVE: The aim of this study was to prepare a simple and reliable method for ceramic bracket debonding, ensuring minimal changes in the enamel structure and an acceptable temperature rise in the pulp. BACKGROUND DATA: Ceramic bracket debonding is based on the principle of degrading the strength of adhesive resin between the tooth and ceramic bracket. The search for a safe and efficient method of adhesive resin removal following debonding has resulted in the introduction of a wide range of instruments and procedures, among which proper use of laser irradiation can be promising. METHODS: The debonding of two types of ceramic brackets utilized a diode-pumped Thulium:Ytterbium-Aluminium-Perovskite (Tm:YAP) microchip laser generating irradiation at a wavelength of 1998 nm (spot size 3 mm; focused by lens), with two power settings (1-2 W). Loss of enamel and residual resin on teeth, as well as rise in temperature inside the tooth were subsequently investigated in detail. RESULTS: A 1W power of irradiation during a 60-sec period resulted in a temperature rise from 3 to 4°C in the approximate root location. This power is also suitable for debracketing from the point of view of damage to enamel lying below the bracket. Only a slight damage to the enamel was registered by SEM compared to conventional bracket removal. CONCLUSIONS: Use of a Tm:YAP laser (wavelength 1998 nm, power 1 W, irradiance 14 W/cm(2), interacting time 60 sec) which is at the same time compact and small enough to be used in the dental practice, together with moderate cooling, could be an efficient tool for debracketing.

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.

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.

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.

Method for evaluating material dispersion of dielectric film in the hollow fiber.

A method is proposed to evaluate the material dispersion of dielectric film in dielectric-coated silver hollow fiber. Cauchy's formulas that characterize the dispersion property were obtained for several commonly used dielectric materials by using the measured data of loss spectra of the hollow fibers. The wavelengths of the loss peaks and valleys in the loss spectra can be predicted more accurately when taking into consideration of the material dispersion. The derived Cauchy's formulas play an important role in the design of infrared hollow fiber for multiwavelength delivery.

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.

Tapered hollow waveguide for focusing infrared laser beams.

A tapered hollow waveguide that can focus a laser beam into a small beam spot is proposed for medical and dental applications. We fabricated hollow tapered optics by using a traveling torch, and the shape was formed as a precise linear taper. For a hollow taper tip with input and output diameters of 700 and 200 microm, respectively, the insertion loss is as small as 0.7 dB in a 10 mm long taper. The hollow taper optic producing a 200 microm spot withstands input energy of 100 mJ. Because a focusing lens is unnecessary at the output end, the laser beam can be introduced into a deep and narrow spot with these tapered optics.

Hollow fiber optics with improved durability for high-peak-power pulses of Q-switched Nd:YAG lasers.

To improve the damage threshold of hollow optical waveguides for transmitting Q-switched Nd:YAG laser pulses, we optimize the metallization processes for the inner coating of fibers. For silver-coated hollow fiber as the base, second, and third Nd:YAG lasers, drying silver films at a moderate temperature and with inert gas flow is found to be effective. By using this drying process, the resistance to high-peak-power optical pulse radiation is drastically improved for fibers fabricated with and without the sensitizing process. The maximum peak power transmitted in the fiber is greater than 20 MW. To improve the energy threshold of aluminum-coated hollow fibers for the fourth and fifth harmonics of Nd:YAG lasers, a thin silver film is added between the aluminum film and the glass substrate to increase adhesion of the aluminum coating. By using this primer layer, the power threshold improves to 3 MW for the fourth harmonics of a Q-switched Nd:YAG laser light.

Bundled hollow optical fibers for transmission of high-peak-power Q-switched Nd:YAG laser pulses.

A hollow-fiber bundle was designed and used to deliver high-peak-power pulses from a Q-switched Nd:YAG laser. An 80 cm long bundle with a total diameter of 5.5 mm was composed of 37 glass capillaries with bore diameters of 0.7 mm. Beam-resizing optics with two lenses were used to couple the laser beam into the bundle. The measured coupling loss due to the limited aperture ratio of the bundle was 2.3 dB, and the transmission loss at wavelengths of 1064 and 532 nm was 0.3 dB. When an inert gas flowed through the bores of the capillaries, the maximum output pulse energy was 200 mJ, which was the limit of the laser used in the experiment. Hollow-fiber bundles withstand irradiation better than single hollow fibers and silica-glass optical fibers do. They are suitable for many dermatological applications because they can be used to irradiate a large area.

Fabrication of a polymer-coated silver hollow optical fiber with high performance.

The techniques for fabricating a hollow optical fiber with an inner silver layer and a cyclic olefin polymer (COP) layer have been improved to reduce the surface roughness of these two layers. The loss spectrum was thereby drastically reduced over a wide wavelength range, from visible to near infrared. Optimization of the COP layer thickness resulted in low loss simultaneously at several key laser wavelengths. Infrared hollow fiber with low loss was developed for Er:YAG and Nd:YAG lasers. It can also deliver green and red pilot beams with low loss. Use of this fiber in therapeutic and pilot lasers should prove useful for research and development in laser medicine.

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.

Multiwavelength laser light transmission of hollow optical fiber from the visible to the mid-infrared.

We report on low-loss multiwavelength laser delivery of hollow optical fiber in a wide wavelength region, from the visible to the infrared. Improved methods of liquid-phase coating were used to fabricate the hollow fiber with inner films of a silver and a cyclic olefin polymer (COP) layer. The surface roughness of the silver layer was reduced dramatically by pretreatment on the inner glass surface with an SnCl2 solution. The COP layer roughness was also decreased by using an ambient atmosphere of tetrahydrofuran (THF) solvent during the COP layer formation. Owing to the smooth surfaces, hollow fiber with optimum COP film thickness for CO2 laser light simultaneously yields low losses for a Er:YAG laser and a red pilot beam. The power durability of CO2 and Er:YAG lasers, as well as the loss properties for the pilot beam, is demonstrated.

Soft-x-ray hollow fiber optics with inner metal coating.

A glass capillary with an inner metal coating is proposed to be used as soft-x-ray fiber optics in medical applications. Based on the results of theoretical calculations, nickel was chosen as the coating material for x rays radiated from a conventional x-ray tube. A nickel-coated capillary was fabricated by electroless deposition, and focusing and collimating effects were observed from measurements of the transmission efficiency of soft x rays. The transmission of a nickel-coated capillary with an inner diameter of 0.53 mm and a length of 300 mm was 10%, which is approximately double that of an uncoated glass capillary.

Hollow-waveguide-based nanosecond, near-infrared pulsed laser ablation of tissue.

BACKGROUND AND OBJECTIVE: Short-pulse solid-state lasers have recently received much attention as new coherent light sources for medical applications, but steady transmission of their high-energy output pulses through a solid quartz fiber is difficult because of the onset of laser-induced breakdown. We previously demonstrated that hollow waveguides could be used to deliver nanosecond laser pulses for tissue ablation. The aim of this study was to determine the optimum laser pulse energy and range of defocused distance for obtaining a deep and sharp ablation channel in myocardial tissue with laser pulses transmitted through a hollow waveguide. STUDY DESIGN/MATERIALS AND METHODS: Cyclic-olefin-polymer-coated silver hollow waveguides of 1 mm in inner diameter and 1 m in length were used. A vacuum-cored scheme was applied to the waveguides to suppress laser-induced air breakdown. Porcine myocardial tissue was irradiated with 300 laser pulses that were delivered through the waveguide in vitro at various laser energy levels and defocused distances, and depths and diameters of channels were measured. Histological analysis of the ablated tissues was also performed. RESULTS: At an ablation energy of approximately 60 mJ/pulse, deep (>4.5 mm) and sharp (depth-to-diameter ratio of > 6) channels were created in tissue in the range of defocused distances of -4 approximately + 0.5 mm. Under these conditions, waveguide bending did not cause a remarkable change in ablation characteristics. Histological analysis of ablated tissue showed limited thermal damage but suggested a certain extent of mechanical effects in the tissue. CONCLUSION: With near-infrared, nanosecond laser pulses delivered through a cyclic-olefin-polymer-coated silver hollow waveguide, efficient and sharp ablation of myocardial tissue can be achieved, suggesting the usefulness of the hollow waveguide as a new flexible delivery system for high-intensity laser pulses.

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.

X-ray opaque waveguide for dentistry.

OBJECTIVE: The aim of this study is the design, realization, and examination of a new x-ray contrast hollow waveguide which will be suitable for x-ray diagnostics or treatment required in medicine, as dentistry, maxiollofacial surgery or oncology. BACKGROUND DATA: With the growing usefulness of laser radiation therapeutic interventions, a strong demand for radiation delivery from the laser source to the interaction place has appeared. For more complicated surgery, especially for internal intervention, an x-ray is necessary. In such cases, as a minimum, the end of the delivery system must be x-ray contrasted to distinguish where the interaction of radiation with tissue would take place. Up to now, neither fiber, hollow waveguide, nor other delivery system have been x-ray opaque. MATERIALS AND METHODS: A new type of hollow glass waveguide was designed, fabricated, and examined as a delivery system for an endodontic treatment. The system is composed from the cyclic olefin polymer coated silver hollow glass waveguide with special covering for x-ray visibility. The inner diameter of the waveguide was 320 microm, the outer diameter was 630 microm, and its length was 100 mm. After the delivery system was created, the hollow waveguide was checked under an x-ray machine and its opacity was measured. For actual treatment, an Er:YAG laser system generating a mid-infrared radiation was used. The root canals of 10 molars were treated endodontically, and the result of that treatment was compared with the common cleaning methods. During treatment, digital x-ray images were taken with conventional files, using this new designed hollow waveguide. RESULTS: The position of a metal instrument demonstrates the quality of opacity after conventional step-back technique. The hollow waveguide is visible in the left tooth canal. A bone density analysis shows no differences between a left (waveguide) and right (tooth) canal. CONCLUSION: It was demonstrated that no differences exist between x-ray opacity of the metal instrument used for endodontic treatment and a special hollow waveguide. The digitalized, three-dimensional image helps to detect a precise position of customary instrument or waveguide in root canal.

Penetration of high-intensity Er:YAG laser light emitted by IR hollow optical fibers with sealing caps in water.

The penetration depth in water was measured for Er:YAG laser light in a high density relevant to clinical applications. Various types of focusing elements were used to guide the light efficiently. We found that the transmission distance depended strongly on the beam shape in the water. When we used a plano-convex type of focusing cap, the penetration depth was larger than that when a dome- or ball-type cap were used.