Ablative An ablative device (such as the CO2 laser) melts or erodes the outer skin much like heat does the surface of a spacecraft during reentry. It's deep and aggressive and usually involves prolonged pain and downtime. Newer non-ablative alternatives are easier to tolerate and may yield good results.
Coherent In regard to light, it means that the waves move in one direction. Laser light is coherent; ordinary light is incoherent, meaning the waves scatter.
Frequency doubling A process in which an input wave generates a wave with twice the frequency and half the wavelength.
Nanometer (nm) The unit of measurement of light wavelength. It is not a measure of strength but length; however (and quite logically), the longer the wavelength, the deeper it can penetrate.
Pulse width The amount of time a pulse of laser light is delivered to the target, often in the realm of a millionth of a second. The faster the pulse, the more painful the procedure, although new cooling techniques can ameliorate some pain.
Q switching A method of obtaining energetic short pulses from a laser. Q-switched lasers are sometimes used to remove tattoos and deep dermal pigmented lesions.
Thermal relaxation time A measurement of tissue cool-down, specifically the time it takes for the tissue to lose 50 percent of the infused energy. Important in determining how long the laser is on the target. If the duration is equal to or shorter than the thermal relaxation time, the heat generated and resulting damage will be confined to the target.