Perhaps the most technically demanding treatments we have at De Luz Medical Aesthetics are the variety of LASER therapies. The word ‘LASER’ should be capitalized because it is an acronym for ‘light amplification by stimulated emission of radiation.’ A LASER consists of a gain medium, an energy pump, a high reflector and an output coupler. The gain medium consists of either a gas, a liquid or a crystal. The material of the gain medium determines the single wavelength of light eventually exiting the device. The different wavelengths of LASER light affect materials differently on the receiving end of the light; more about this later. The different types of LASERs are typically named for the their constituent gain mediums, for example KTP (potassium titanyl phosphate), alexandrite, Nd:YAG (neodymium-doped yttrium aluminum garnet), CO2.
The energy pump uses either electricity or flash lamps to excite electrons in the gain medium. When the electrons return to their original state they emit light photons. The light photons then bounce between the high reflector and the output coupler. When the light photons reach the correct pattern they pass through the output coupler as LASER light. The output coupler ensures the light photons are collimated and coherent. The terms collimated and coherent refer to the alignment of the waves of light energy exiting a LASER. The waves of LASER light are all one ‘color’ or monochromatic, traveling parallel or collimated, and the waves are in step or coherent.
The three properties of LASER light, monochromatic, collimated and coherent, allow the beam to deliver concentrated energy differentiating it from a flashlight, for example. One property of LASERs, the wavelength of light, determines its interactions with the human body. Different wavelengths pass through to different depths and affect different structures in the body.
Ultraviolet (UV less than 390nm, nm = nanometers or one billionth of a meter) and infrared (IR above 750nm) light penetrate living tissue less than wavelengths of light in the visible spectrum. UV and IR light typically effect only the epidermis. Light in the visible spectrum, from about 390-750nm, can penetrate living tissue into the subcutaneous (just below the skin) tissues. Additionally, the depth of penetration for any LASER can be increased by increasing the power output of the LASER. For example, a CO2 laser can penetrate into the dermis but only in small spots for a fractional resurfacing treatment.
The wavelength of light also determines the type of tissue affected by the LASER. LASERs affect three main types of molecules: melanin, hemoglobin and water. The absorption of light energy by melanin and hemoglobin overlap significantly. Melanin and hemoglobin absorb LASER light energy with wavelengths in and around the visual spectrum. When a molecule absorbs the LASER light energy, it heats up. Depending on the energy applied, the heat can damage or destroy the molecule and even damage or destroy surrounding structures. For example, heating the melanin inside a hair follicle can damage or destroy the hair follicle. The graphs demonstrate which LASERs affect the different molecules and to what degree. For example, an Er:YAG LASER at 2940nm has great affinity with water but a Nd:YAG LASER at 1064nm has little to no affinity with water. Said a different way, water can absorb 10,000 times more energy from an Er:YAG LASER than a Nd:YAG LASER.
But, what can LASERs do for you? Next week.
Thank you for time and attention,
Robert Zieber, MD
De Luz Medical Aesthetics