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The "Laser"
I chuckle to myself when I think about lasers. I expect Austin Powers to put air quotes around the word when I say it. I find that many people use the term as if it was a magical device that can do anything – including make a scarless incision. It can’t. Lasers are just a way to apply energy to a spot. All you can change is the size of the spot, the length of time the laser is on, and the color (and thereby the energy) of the laser. That’s pretty much it. (Physicists have a term called fluence that measures the amount of energy delivered per unit area. Higher fluence = more energy. Don’t remember that or people will think you are a geek.)
My first experience with medical lasers was in 1984. I was a surgery intern and happy to be watching a case of hemorrhoids (yes, hemorrhoids) being removed with a laser. The attending physician was proud to show me how his new toy worked. He pointed the hand piece of the laser at a wooden tongue depressor and stepped on the pedal. Sure enough – the laser beam immediately went right through the wooden stick. Unfortunately it kept going, striking the paper drapes covering the patients legs. Poof, a small fire started. The nurse was totally calm and just dumped a basin of water on the smoking paper. No harm done, but I realized that this was not a simple toy.
So what types of medical lasers are there and what are they used for?
The carbon dioxide laser was developed at Bell Labs in 1964. It is an efficient laser that emits in the infrared part of the spectrum. The wavelength of the CO2 laser is absorbed by water and therefore heats tissue very well. It is used in facial resurfacing to remove wrinkles. By controlling how long the pulse lasts and the pattern of pulses, very precise layers of skin can be removed. It is often used with a computer pattern generator for perfect application of the pulses.
Nd:YAG is a type of laser also developed by Bell Labs in the same year. Nd stands for neodymium. The initials YAG is for yttrium-aluminium-garnet. (Now you see why we refer to it by its initials.) This laser emits infrared light (1064 nm). It is used in ophthalmology and can be used to remove skin cancers. Gynecologists use it during hysteroscopy to treat certain uterine conditions. It’s most common cosmetic use is for laser hair removal and to remove spider veins from the face and legs. It can also aid in removing fungus from the fingernails and toenails.
Er:YAG is a similar laser. Instead of neodymium, erbium is used. This laser emits further into the infrared spectrum (2940 nm) and is strongly absorbed by water. It is used in laser resurfacing of the skin to treat acne scarring, wrinkles, and melasma (patchy pigmented areas of the skin). It also can be used to remove warts. Dentists and oral surgeons use this laser to cut bone.
Q-Switched Lasers – Alexandrite, Ruby, Nd:Yag, Tunable Dye. OK, another geeky term, but a very useful technique. Q-Switching allows the laser to have high energy pulses instead of a continuous beam. That makes these lasers ideal for tattoo removal. From the Wikipedia article on tattoo removal:
Q-switched Frequency-doubled Nd:Yag: 532 nm. This laser creates a green light which is highly absorbed by red and orange targets. Useful primarily for red and orange tattoo pigments, this wavelength is also highly absorbed by melanin (the chemical which gives skin color or tan) which makes the laser wavelength also effective for age spot or sun spot removal.
Q-switched Ruby: 694 nm. This laser creates a red light which is highly absorbed by green and dark tattoo pigments. Because it is more highly absorbed by melanin this laser may produce undesirable side effects such as pigmentary changes for patients of all but white skin.
Q-switched Alexandrite: 755 nm. Similar to the Ruby laser, the alexandrite laser also creates a red light which is highly absorbed by green and dark tattoo pigments. However, the alexandrite laser color is slightly less absorbed by melanin, so this laser has a slightly lower incidence of unwanted pigmentation changes than a ruby laser.
Q-switched Nd:YAG: 1064 nm. This laser creates a near-infrared light (invisible to humans) which is poorly absorbed by melanin, making this the only laser suitable for darker skin. This laser wavelength is also absorbed by all dark tattoo pigments and is the safest wavelength to use on the tissue due to the low melanin absorption and low hemoglobin absorption. This wavelength is the wavelength of choice for tattoo removal.
Dye modules are available for some lasers to convert 532 nm to 650 nm or 585 nm light. Which allows one laser system to safely and effectively treat multi-color tattoo inks.
Dye lasers use an organic dye mixed with a solvent that is stimulated by an high energy external light source to lase. Mirrors are used to increase the energy. Then cavities or resonators are used to tune the output. By selecting different dyes the output color can be changed. They are commonly used to treat port-wine stains and other pigmented lesions of the skin. The can also be used to decrease scarring and to make the skin tone more even. By matching the dyes to the different ink colors they can also be used for tattoo removal.
IPL is the last one to discuss. Intense Pulsed Light is technically not a laser. It produces very high intensity light in very short pulses. IPL is the most common form of hair removal ‘laser’ and is roughly as effective as the Nd:YAG mentioned above. It is also used to treat rosacea, birth marks, sun damaged skin, and scarring.
And that should do it for today. You are now more educated. Enjoy!
Laser hair removal