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The coagulative effect of the conventional CO2 surgical laser at 10.6 micrometers is usually sufficient for homeostasis during surgery, but at laser wavelengths approaching 3 micrometers , the absorption depth is very shallow, and all the laser/tissue interaction is very close to the surface. Where ablation of surface tissues must be combined with a more penetrating laser action for coagulation or tissue bonding, auxiliary wavelengths are required. Significant penetration into the remaining unablated tissue is needed for coagulation of large blood vessels, as well as for generalized control of bleeding or seeping, or for more gentle, but even, heating of the cut surfaces of blood vessels, nerves, and other tissues as part of tissue anastomosis or bonding procedures. Also, large volumes of tissue are often removed as rapidly as possible; this needs deep penetration of the energy over a wide area. All of these effects call for wavelengths well away from the water absorption peak near 3 micrometers . Both ZrF4 and sapphire optical fibers are sufficiently transparent in the visible and IR regions of the spectrum to pass an ablative wavelength near 3 micrometers , coagulative and tissue bonding wavelengths in the shorter IR, and another auxiliary beam in the visible to serve as a marker which will remain in precise optical alignment with the active and invisible IR beams. The control of the relative proportions of the various active wavelengths will allow selection of the precise surgical effect to be obtained, ranging from pure ablation to coagulation only or tissue bonding alone with all combinations in between. The concept of the multiwavelength laser delivery system will certainly be popular in the future whenever such instrumentation becomes sufficiently available for its utility to be widely recognized.
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