Delivery of therapeutic laser light using a singlemode silica fiber for a scanning fiber endoscope system

The feasibility of integrating laser-based therapy using a singlemode fiberoptic delivery system in an endoscopic procedure has been investigated. The maximum transmissible optical power in a high-resolution scanning fiber endoscope system is limited by the requirement for small-core singlemode light propagation, thus impeding the capacity for optical therapies. Since the scanning fiber endoscope can be fabricated from low-cost components, the maximum power capacity of the singlemode optical fiber can be approached in the single use of the medical device. In preparation for future tissue studies, 29.4 micron nominally thick samples of Low Density Poly-Ethylene (LDPE) were used as standardized targets. To model the transient pulse-sample interaction of a scanning fiber endoscope, a pulsed, 50mW, 404nm Coherent CubTM laser system was used to replicate the conditions present in a scanning fiber endoscope that images by measuring the backscatter of combined red, green, and blue laser illumination. Preliminary tests indicate that thermal damage thresholds in LDPE are 120kW/cm2. Dwell time and repetition characteristics were investigated and thermal damage thresholds for full-power single pulses was approximately 1ms, using 0.125 NA lens to the LDPE film. The higher-power 405 nm laser diodes are able to be directly modulated so that small regions of interest within the scanned sample can be irradiated for diagnosis (autofluorescence) and therapy (cutting and necrosis). Future studies will integrate the violet laser light with red, green, and blue light for frame-sequential imaging, diagnosis, and therapy.

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