Brett A. Hooper, George C. LaVerde, and Daniel Chang
Center for Emerging Cardiovascular Technologies, Department of Biomedical Engineering, Duke University
Precise laser surgery is possible using laser pulses at wavelengths that are strongly absorbed at the surface of tissue. However, pulses at these wavelengths (far UV, far IR) are not compatible with fiber optic transmission, making endoscopic surgical procedures inside the body difficult. New fibers (hollow waveguides and chalcogenide glass) are showing promise for efficient transport of infrared wavelengths, where there are substantial differences in the absorption spectra of lipid-rich and water-rich tissues. We measure the interaction of light with tissue at the interface between transparent, high-refractive-index optical materials (prisms and fibers) and tissue. For high-light levels, such as laser light, precise superficial tissue ablation is achieved with evanescent waves generated at a sapphire-tissue interface by a free-electron laser (FEL). For low-light levels, we have developed a novel approach using a modified spectrophotometer to determine the optical properties of tissue in vivo. In particular, the refractive index and extinction coefficient can be obtained for wavelengths from 2 to 10 
m. A new class of precise, controlled laser surgical tools may be achieved in this novel approach for use in endoscopic procedures, where the goal is to couple the diagnostic and therapeutic uses into one catheter.