Essentials for predictable CO2 laser micro-beam tissue interactions

Abstract

Many laser surgery practitioners administer therapeutic laser treatment by relying on a sensory mechanism known as “Tactile Feedback”. This sensory interface with the laser’s delivery devices provides a sensory “perception” that can accurately predict the therapeutic outcome. The effectiveness of this acute sensory mechanism must assume a stable TEM00 beam distribution. Only then can “predictable therapeutic results” be perceived and achieved.The lowest order TEM00 mode with the nearly Gaussian intensity distribution has the lowest laser cavity losses1 and hence will remain fairly intact even while sustaining losses through the delivery system. Other energy losses due to optical diffraction limits and atmospheric absorption (i.e. smoke and assist gases) can be overcome by the proper beam profile mode optimization. In order to produce an interaction that limits the thermal damage to tissues adjacent to the target site, frequent visualization of the beam distribution is essential. This not only assures aesthetically appeasing results, but also provides a desirably small spot size and thus a longer incision depth.All CO2 surgical laser resonators sustain losses from thermal gradients that can cause departures from the Gaussian beam distribution. Infrared imaging devices such as commercially available phosphor plates, provide an excellent means of displaying invisible IR laser radiation in real-time. The trained laser operator can then perform the necessary adjustments for beam profile optimization prior to laser utilization. Unfortunately, many surgical CO2 laser systems have either impractical or no means of providing user access to the output coupler where this mode adjustment is performed. Such access to the output coupler may not be possible in a condition of normal operation. However, at least by analyzing the mode profile externally, can a determination be reached as to whether or not to proceed with tissue irradiation.Many laser surgery practitioners administer therapeutic laser treatment by relying on a sensory mechanism known as “Tactile Feedback”. This sensory interface with the laser’s delivery devices provides a sensory “perception” that can accurately predict the therapeutic outcome. The effectiveness of this acute sensory mechanism must assume a stable TEM00 beam distribution. Only then can “predictable therapeutic results” be perceived and achieved.The lowest order TEM00 mode with the nearly Gaussian intensity distribution has the lowest laser cavity losses1 and hence will remain fairly intact even while sustaining losses through the delivery system. Other energy losses due to optical diffraction limits and atmospheric absorption (i.e. smoke and assist gases) can be overcome by the proper beam profile mode optimization. In order to produce an interaction that limits the thermal damage to tissues adjacent to the target site, frequent visualization of the beam distribution is essential. This not only assures aest...