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A simple color separation technique for solar tissue photocoagulation

Aiming at studying solar photocoagulation in biological tissue with both low energy and high energy portions of solar spectrum, a simple color separation technique is proposed. The chromatic aberration characteristic of Fresnel lens is exploited to achieve color separation by a plane mirror with a large central elliptical hole, reflecting the solar radiation above 600nm to one fused silica light guide, while allowing the passage of the remaining radiation to another guide. ZEMAX™ ray-tracing code is used to optimize the performance of each optical component. To attain a stable solar coagulation, the prototype is tested on a two-axis solar tracker. The ex vivo measurement is performed on chicken breasts at the solar power level of 30W and the exposure time of 60 seconds, attaining a uniform coagulation over a large area of 15mm x 15mm. A strong dependence of the penetration depth on wavelength is observed. Our cost effective solar photocoagulation prototype produces the same type and extent of tissue coagulation ordinarily achieved with surgical laser equipment.