In soft-tissue laser surgery, a highly focused laser beam vaporizes soft tissue with a high water content. The laser makes small incisions when the beam is focused on tissue; the focal spot size can be as small as 100 µm, but the most widely used in practice is 400 µm (0.4 mm). When the beam is defocused, the intensity of the laser light diminishes, and it can be used for cauterization of small blood vessels and lymphatics, therefore decreasing post-operative swelling.
Soft-tissue laser surgery is used in a variety of applications in human (general surgery, neurosurgery, ENT, dentistry, orthodontics, and oral and maxillofacial surgery) as well as veterinary surgical fields. A laser beam has a natural sterilization effect: it evaporates bacteria, viruses and fungi, which leads to a decrease in local infections. Probably most important, the laser decreases post-operative pain by sealing nerve endings. Soft-tissue laser surgery is differentiated from hard-tissue laser surgery (bones and teeth in dentistry) and laser eye surgery (eyesight corrective surgeries) by the type of lasers used in a particular type of laser surgery.
Hard tissue surgical lasers are dominated by Er:YAG lasers operating at the wavelengths of 2.94 µm. Laser eye surgery utilizes excimer lasers in the UV range of wavelengths. Unlike many solid-state and diode lasers in the visible and near infrared wavelength range (600-2,000 nm), the carbon dioxide laser wavelength (10.6 µm) is highly absorbed by in-vivo soft tissues containing water. Furthermore, modern CO2 laser technology makes these lasers far more affordable than solid-state Er:YAG lasers, which also feature a wavelength that is highly absorbed by water. Because of their wavelength and precision, CO2 lasers remain the dominant soft-tissue surgical lasers. The CO2 laser remains the best surgical laser for the soft tissue where both cutting and hemostasis is achieved photo-thermally (radiantly). Surgical laser systems are differentiated not only by the wavelength, but also by the light delivery system: flexible fiber or articulated arm, as well as by other factors. Minimally invasive interaction of ultrashort pulse lasers with biological tissues has been investigated to understand their characteristics and mechanism and how they can be utilized to advance surgical applications of lasers.
The key to the success of soft tissue lasers is their ability to cut and coagulate the soft tissue at the same time. Laser light’s wavelength determines how it is absorbed by objects. Lasers of different wavelengths produce different effects on tissue. For practical surgical lasers on the market today (diode, erbium and CO2 lasers), the laser light energy is transformed, through absorption, into the heat inside the tissue leading to elevated tissue temperatures that, in turn, can result in tissue ablation and coagulation. Such laser-tissue interaction is referred to as photo-thermal.
A CO2 laser consists of the following interacting elements: an active medium confined between two mirrors: a total reflector and a partial reflector. The main difference between laser light and ordinary light, such as that produced by a light bulb, is directionality, i.e. it is highly collimated. Such collimated, monochromatic and coherent beam of light is focusable to a very small focal spot that can be used for tissue incision, excision and ablation of soft biological tissue.