Browsing by Subject "Medical Lasers"

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    Hollow core photonic bandgap fibers for medical applications
    (2009) Vural, Mert
    The design, fabrication and characterization of photonic band gap (PBG) based optical polymer fibers is discussed. Unlike conventional total internal reflection (TIR) fibers, used primarily in telecommunications, PBG fibers can be made hollow core and can be used to guide infrared radiation of any wavelength, a property known as wavelength scalability. Since the electromagnetic radiation is transmitted in the hollow core of the fiber, the intrinsic absorption of the fiber core as well as the insertion Fresnel losses at front and end faces are avoided, giving rise to extraordinarily high power densities to be delivered. The fiber production line includes material characterization, and the design of nanoscale quarter wavestacks using common thermoplastic polymers (poly ether sulphone and poly ether imide) and chalcogenide glasses (As2S3, As2Se3, Ge15As25Se15Te45). The fiber preform is fabricated using rolling mechanism of thermally evaporated chalcogenide glasses on large area polymers. Subsequently, the fiber preforms are thermally drawn to obtain nano-structured PBG fibers.Two different fibers are designed and produced, signifying wavelength scalability of the overall process, for the widely used holmium (Ho:YAG) and carbon dioxide (CO2) medical lasers. The transmission characteristics of the fibers proved that they can be used to safely deliver 15Wlaser power, along a 3 meter fiber with external diameter of 1.5 mm and hollow core diameter of 0.5 mm, corresponding to a laser power density of 1kW/cm2 with a loss of -10dB/m. The PBG fibers are expected to be widely used in high precision surgical laser for incision, photoablation and coagulation where infrared radiation is the radiation of choice for its superior laser-tissue interaction properties.
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    ItemOpen Access
    Polymer / glass hollow-core photonic band gap fibers for infrared laser beam delivery
    (2011) Köylü, Özlem
    Photonic band gap fibers are proposed for the medical applications of laser light transmission into body. Conventional optical fibers guide light via total internal reflection. Due to light guiding mechanisms and materials they have limited frequency range, fiber flexibility and laser power. On the other hand, it is possible to scale operating wavelengths of PBG fibers just by changing a few parameters during fabrication process. Besides, hollow core of PBG fibers eliminates material absorptions and non-linearities during light guiding. PBG fiber production starts from material characterization; and selection; and continues with fiber design, thin film coating, preform preparation and fiber drawing. Studies on theoretical calculations and material properties have shown that best candidate materials for CO2 laser delivery are As2Se3 and poly-ethersulfone (PES). For this purpose, As2Se3 coated PES films are rolled to form a preform and consolidated before thermal drawing. Characterization of drawn fibers indicated that CO2 laser can be transmitted with loss levels of > 1 dB/m and 32 W output power is observed from a 1.2 m long fiber. After fabrication and characterization of PBG fibers, a prototype infrared laser system is built and tested on various applications. In our group laser tissue interactions are examined to see effectiveness of CO2 laser on tumor tissue. Experiments showed that tumor tissue is affected in a very distinctive way compared to healthy tissue. Absorption of cancerous lung tissue at CO2 laser wavelength (10.6 µm) is higher than absorption of healthy tissue at the same wavelength. This study proposes a wide use of PBG fiber for not just CO2 lasers, but also other laser systems used in different medical operations, such as Ho:YAG lasers. PBG fibers for high power laser delivery are novel structures for fast, painless and bloodless surgeries.