Laser setting parameters
There are five core parameters that a practitioner should consider when operating a laser or light device.
The first is: wavelength.
The practitioner chooses the wavelength to utilize based on the target or chromophore they are treating. With laser or light devices, there are three different exogenous targets that a practitioner can treat: melanin, blood or water. Melanin is defined as: a dark brown pigment that is found in human skin, hair and iris of the eye. Blood consists of Hemoglobin, which is defined as: a red protein found in blood vessels. The water chromophore refers to the water located in human tissue.
Not all wavelengths are safe for all skin types. Generally the shorter the wavelength, the more the wavelength is absorbed by melanin and blood. Thus, a 755nm wavelength is not as safe for darker skin types as a 1064 nm wavelength, due to its absorption by melanin (the brown pigment in skin). The longer the wavelength, the more absorbed it is by water and less so by melanin, which is why a 1064 nm wavelength is safer for darker skin types. An example of a wavelength absorbed by water is the 1550 nm wavelength, which Candela offers on the Frax 1550 applicator.
The second parameter a practitioner should consider when operating a laser or light device is spot size. Depending on the target (water, blood or melanin) and its depth in the skin, it is important to remember that the larger the spot size, the deeper the depth of penetration. With a large spot size, there is less scatter of the laser light within the tissue (Farkas MD, Hoopman MD, Kenkel MD. “Five Parameters You Must Understand to Master Control of Your Laser/Light Based Devices.” The American Society for Aesthetic Plastic Surgery, Inc. 33, 7, 1059-1064). Therefore, if the practitioner is attempting to target a chromophore that lays deep within the skin surface, they may want to consider using the largest spot size that will give an appropriate clinical endpoint.
The third parameter a practitioner should consider when operating a laser or light device is the fluence to use. Fluence is defined as the laser pulse energy per spot size used. When considering what fluence to use, this will determine how much energy is being used to destroy the target (blood, water or melanin).
The fourth parameter to consider is pulse width, also known as pulse duration. The pulse width refers to the amount of time the target is exposed to the laser or light energy. Depending on the size and volume of the target, the pulse duration will be adjusted. With larger, denser or thicker targets the practitioner may want to consider to lengthen the pulse width, with smaller, finer targets the practitioner may want to shorten the pulse duration. A larger, denser target needs more exposure time to laser or light energy to be successfully destroyed verses a smaller, finer target. On the GentleMax Pro® device, the pulse duration is measured in milliseconds and can be adjusted. On the PicoWay® device, the pulse duration is measured in picoseconds and is automatically set.
The fifth and final parameter to consider when selecting laser or light device settings is cooling. Cooling on energy based devices allows for a practitioner to protect the epidermis. The practitioner is encouraged to identify the chromophore and its depth within the skin, the patients skin type and nature of the chromophore they are looking to treat. With higher fluences or darker skin types, the practitioner may want to use high cooling settings. If the practitioner is looking to target epidermal melanin in a lighter skin type, they may want to use little to no cooling.
Farkas MD, Hoopman MD, Kenkel MD. “Five Parameters You Must Understand to Master Control of Your Laser/Light Based Devices.” The American Society for Aesthetic Plastic Surgery, Inc. 33, 7, 1059-1064.