The principle on which this type of technology is based requires the use of nonablative wavelengths of light to selectively coagulate tissue in the epidermis and dermis. The light is focused by sending it through micro-lens arrays to create multiple beams of light or by focusing one beam and using a scanner to create hundreds of coagulation columns ranging from 300 pm deep to 1.4 mm in depth, depending on the energy per microbeam. This reaction spurs the body’s natural healing response to remove and replace the coagulated tissue, stimulating fibroblast collagen production, and subsequently resurfacing the tissue (Fig. 4.12). This is different than in the past when ablative erbium:YAG and CO2 lasers were used to totally remove the top layer of the epidermis and a portion of the dermis, often called full – surface ablation as opposed to fractional ablation discussed later. Although the results were, and still are very good, this type of skin ablation creates a large amount of down time, and an increased risk of complications. These include but are not limited to, infection, hypertrophic, and atrophic scarring, and permanent hypopigmentation.
By using different lasing materials and “doping methods”, fundamental wavelengths can be shifted for different uses. In the case of nonablative skin resurfacing, the goal of researchers was to have the ability to create the same type of healing effect as seen in earlier ablative treatments, but without the significant downtime or increased risk of complications. Wavelengths in the 1,320-1,580 nm have been tried at this point, with varying success. The key in this case is to have a wavelength that has a good penetration into the skin for depth, and has a low collagen denaturation threshold (level of thermal damage at which the tissue will coagulate). This combination can be found in the 1,530-1,590 nm range, which is where most of the more successful systems in the market have set their beam wavelengths.