Effects of nonorthogonal CO2 laser-beam delivery on the geometry of the resulting crater: a qualitative description.
New experimental data obtained using previously described methodologies relating to types, power densities, and media of CO2 lasers are presented. This report considers a nonorthogonal beam direction to the sample's surface. The CO2 laser beam does not always produce clean cuts. This is a potential danger during routine operations but might be useful in special applications in which a curved crater or cut would be preferable to a traditional rectilinear one. In-vitro investigations have shown that the angle theta between the beam direction and the sample's surface determines both the degree of curvature and its direction with respect to the surface. The phenomenon can apparently be reproduced each time the direct beam hits a reflecting surface during propagation and continues to perforate the sample afterwards at the same incoming angle: only the second segment of the crater always appears curved. The curved crater lies totally on the geometric plane that is perpendicular to the reflecting surface and contains both the point of the beam-spot position and the point of reflection. From the point of view of surgical application, the probability of occurrence of this phenomenon is high because of the frequent and dramatic tissue density variations encountered over a very short period of time. Muscles, bones, tendons, fat, blood, skin, and vapors create favorable conditions to allow partial reflections along the direction of the cut. A possible explanation for the phenomenon could lie in the energy conservation process within the crater. The modified internal symmetry of the crater is thus a consequence of the reflection process combined with the power density reduction along the "reflected" section of the crater.
Canestri
F
F
Hewlett-Packard Company-Medical Products Group Europe, Boeblingen, Germany.
D053685:Laser Therapy; D008962:Models, Theoretical; D015203:Reproducibility of Results