In microsurgical CO2-laser treatments in natural orifices of the body, like nasal, oral or laryngeal operations or similar approaches in other medical fields, the laserbeam is directed via a micromanipulator into a rigid endoscope, like a speculum or a microlaryngoscope. A small operating spot size is achieved by focusing the beam of relatively large initial diameter, the focal cone being fed into the endoscope by means of a beam deflecting mirror. Since the beam deflecting mirror may cover parts of the microscopic viewing field, in some micromanipulators it is mounted out of the optical microscope axis. The aiming of the invisible working beam is accomplished by a visible collinear aiming beam, which, however, has different geometric and optical properties. By these complex working conditions a number of beam alignment problems, which may lead to unnoticed laser bums, is encountered:
misadjustment of working and aiming beam in x- and y-coordinates (beam coincidence)
differences of focal planes due to wavelength-dependent dispersion
parts of the beam passing outside the endoscope due to paraxial mirror
reduced working field due to wide focal cones at a high focus micromanipulator
reduced depth of focus with a high focus micromanipulator
disagreement of optical axes of the operation microscope and the hand-held speculum
misinterpretation of beam position because of smaller focal cone of the aiming beam
These items and procedural ways to avoid patient’s skin bums are demonstrated.