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Optical fibers with enhanced performance for excimer laser power transmission at 308 nm

Power transmission of xenon chloride excimer lasers through optical fibers is necessary for medical applications where tissue removal is performed within the human body. The most important application at present is excimer laser coronary angioplasty. Typical levels of energy densities applied by optical fibers for this application cause color center generation in fused silica leading to transmission decrease called photodegradation. This effect depends essentially on the grade of the fused silica. Important parameters are fiber length, pulse duration, energy density, and the irradiated cross sectional area of the optical fiber endface. For a new grade of core material the influence of these parameters on the transmission performance is described. The obtained material improvement leads to a significant reduction of the observable transmission decrease as a function of the number of laser pulses applied. Thus continuous operation of the laser in the region of the typical transmission plateaus at considerably higher and constant energy levels at the distal fiber end becomes feasible. This offers a new option for more reliable dosimetry in medical applications.