Excerpted from material published by: Albert Poet MD FACS

Since their development in 1960, lasers have become powerful and indispensible tools, used in almost every aspect of technology. Laser applications in medicine and surgery have similarly evolved, and while medical lasers have never become the "magic ray" that some had hoped, they have become powerful and indispensible tools in clinical practice as well.

There are many medical laser systems available today, but they all use the principal of selective photothermolysis, which means getting the right amount of the right wavelength of laser energy to the right tissue to damage or destroy only that tissue, and nothing else.

• The right wavelength: Most medical laser devices deliver only one wavelength of laser light, and the laser surgeon must choose the right wavelength for the specific tissue involved. Some lasers can be "frequency doubled", and can deliver two wavelengths of laser light, and a very few are tuneable over a narrow range of wavelengths. Some lasers can be used in different modes, for example, Q-Switched and long-pulse.
• The right amount of laser energy: Almost all medical lasers allow the laser surgeon to adjust the power setting and duration of the laser pulse. As a general rule, the length of the laser pulse is as important as the wavelength or the power setting in determining its medical use. Lasers can operated in continuous wave (CW) or pulsed mode. CW lasers emit a steady beam for as long as the laser medium is excited. If this steady beam is held on tissue longer than the thermal relaxation time, excessive heat will be conducted into normal tissue, which may delay healing and increase scarring. All CW lasers may be pulsed, either mechanically using a shutter, or by electronic or photonic means. Pulsed lasers emit light in individual pulses, which may be long-pulsed (thousandths of a second) or short-pulse (millionths of a second). Q-Switching allows the laser to store energy between pulses, enabling very high power output.
• Getting the laser energy there: The laser surgeon uses a "delivery device" to get the laser energy to the tissue. These devices include special fiberoptic cables with handpieces, or articulated arms, in which specially reflecting mirrors are mounted in tubes which rotate about the axis of the mirrors. The laser light is reflected from mirror to mirror through the tube out to the patient. Special devices may be attached to the handpieces of either fiberoptic cables or articulated arms, including slit lamps for use on the eye, operating microscopes for use in the ear and throat, insulated fibers for use with endoscopes in gastrointestinal and bronchial surgery, and Scanners, which scan the laser beam in a preset pattern and limit the time a CW laser beam dwells on the target tissue.

Presented below is an overview of medical lasers currently in general use. Certain lasers are only used for very specific conditions. Some conditions can be treated many ways, including by several different lasers, as well as by non-laser methods. Medical Lasers are not magic-they are only tools, and one should always select the right tool for the right job!

CO2 Laser: Often referred to as the "Surgical Laser", the action of the CO2 laser most resembles traditional surgery. Unlike any other medical laser, its action on tissue is directly visible as it's used. The CO2 Laser was the first laser widely used by surgeons, and is still the most used of all the medical lasers. Strongly absorbed by water, which constitutes over 80% of soft tissue, the CO2 laser emits continuous wave (CW) or pulsed far infrared light at 10,600 nanometers (nm), which can be focused into a thin beam and used to cut like a scalpel, or defocused to vaporize, ablate, or shave soft tissue. The CO2 Laser may be operated in pulsed mode or used with scanning devices to precisely control the depth and area of ablation. Uses include:

• Removal of benign skin lesion, such as moles, warts, keratoses
• As a "laser scalpel" in patients or body areas prone to bleeding
• "No-Touch" removal of tumors, especially of the brain and spinal cord.
• Laser surgery for snoring
• Shaving, dermabrading, and resurfacing scars, rhinophyma, skin irregularities
• Cosmetic Laser Resurfacing for Wrinkles

Argon Laser: One of the first lasers to be used clinically , the Argon (or argon-ion) laser is a continuous wave (CW) gas laser that emits blue-green light at 488 and 514 nm. Argon laser light is strongly absorbed by hemoglobin and melanin. Although the beam may be mechanically pulsed, there's significant non-selective heating in surrounding tissues, thus increasing the chance of scar formation. Delivery is through a fiberoptic cable to a handpiece, slit lamp, or operating microscopye. Uses include:

• retinal and inner ear surgery
• treatment of thick or nodular port wine birthmarks
• facial spider veins
• small dark moles (junctional nevi)
• cherry hemangioma

YAG Lasers: YAG lasers use a Yttrium-Aluminum-Garnet crystal rod as the lasing medium. Dispersed in the YAG rod are atoms of rare earth elements, such as neodymium (Nd), Erbium (Er) or Holmium (Ho), which are responsible for the different properties of each laser. All YAG lasers may be operated in continuous,/pulsed, or Q-Switched mode, although a particular medical device is usually only capable of one or the other. Continuous and pulsed delivery is through fiberoptic cables, either bare-fiber or through handpiece or scanners, and Q-Switched delivery, because of the very high power, is through an articulated arm.

• Nd:YAG Laser: A true workhorse, the Nd:YAG emits a near-infrared invisible light at 1064nm or 1320nm. It may be delivered in CW or "long pulsed" (millisecond domain) mode through a fiber to a sapphire tip to cut tissue, or because of its deep penetration, used to directly coagulate tissue. The Q-Switched Nd:YAG is effective for black tattoo ink , and has been used with fair results for hair removal. Millisecond-range Nd:YAG laser light is very effective for long-term hair removal.
• KTP Laser: When Nd:YAG laser light at 1064 nm is passed through a potassium-titanyl-phosphate (KTP) crystal, the wavelength is halved to 532 nm, a brilliant green light used in CW mode to cut tissue, in pulsed mode for vascular lesions including facial and leg veins, and in Q-Switched mode for red/orange tattoo pigment. Delivery is through an insulated fiber, fiber handpiece, scanner, or microscope for CW/pulsed mode, and articulating arm for Q-Switched mode.
• Er:YAG Laser: Often referred to as the "Erbium" laser, it emits a mid-infrared beam at 2940 nm, which coincides with the absorption peak for water. Its principal use is to ablate tissue for cosmetic laser resurfacing for wrinkles. The Erbium laser has been advertised to offer advantages of reduced redness, decreased side effects and rapid healing compared to the pulsed or scanned CO2 laser, but does so by its limited penetration into tissue, which limits the results compared to the more versatile CO2 laser. It has also been used as a dental drill substitute to prepare cavities for filling.
• Ho:YAG Laser: Relatively new to the medical/dental fields, the Ho:YAG laser emits a mid-infrared beam at 2070 nm. It's principal use is to precisely ablate bone and cartilage, with many applications in orthopedics for arthroscopy, urology for lithotripsy (removal of kidney stones), ENT for endoscopic sinus surgery, and spine surgery for endoscopic disc removal. The Ho:YAG laser was recently approved for TURP (prostate removal).

Ruby Laser: The Ruby laser emits red light with a wavelength of 694 nm. The lasing medium is a synthetic ruby crystal of aluminum oxide and chromium atoms, which is excited by flashlamps. The first laser system to be built by T. H. Maiman in 1960, early ruby laser systems were used for retinal surgery, but weren't suitable for dermatologic work until the development of Q-Switching technology in the mid 1980's. Ruby laser light is strongly absorbed by blue and black pigment, and by melanin in skin and hair. Modern ruby laser systems are available in Q-Switched mode, with an articulating arm, "free running" (millisecond range) mode with a fiber optic cable delivery, or as dual mode lasers. Current uses include:

• Treatment of tattoos (Q-Switched mode)
• Treatment of pigmented lesions including freckles, liver spots, Nevus of Ota, cafe-au-lait spots (Q-Switched mode)
• Laser Hair Removal (free-running mode)

Alexandrite Laser: Similar to the Ruby Laser, the Alexandrite Laser contains a rod of synthetic chrysoberyl, a gemstone discovered in Russia in 1830 on Czar Alexander II's 13th birthday. It emits a deep red light at 755 nm, and has properties similar to the ruby laser. It's slightly longer wavelength permits slightly deeper penetration into skin, with slightly less absorption by melanin. Prinicipal uses include laser hair removal in millisecond-range pulsed mode, and tattoo removal in Q-Switched mode.

Pulsed Dye Laser: Because the yellow light at 577-585 nm coincides with the peak absorption of hemoglobin in blood, the Pulsed Dye Laser (PDL) is useful to treat vascular lesions. A lasing medium of rhodamine dye is excited by flashlamps, emitting a pulse in the range of 450 microseconds (1500 microseconds in some of the newer PDL's), just less than the thermal relaxation time of minute blood vessels. Originally developed in the late 1980's, the Pulsed Dye Laser became the preferred laser for the treatment of vascular lesions, including spider veins, strawberry birthmarks and port wine stains, replacing the Argon Laser because of the PDL's decreased heat damage and decreased chance of scarring. However, the PDL's short pulse and high absorption ruptures the targeted blood vessels, causing unsightly purpura (black and blue marks) which can last up to 2 weeks. Currently, less expensive, more reliable green light lasers such as the KTP and other Frequency doubled Nd:YAG are used for most vascular lesions. The Pulsed Dye Laser remains the treatment of choice for:

• Port Wine Stains, especially in infants and children
• Laser treatment of thick, red scars

Copper Vapor Laser: Vaporized copper bromide is the lasing medium in the Copper Vapor Laser (CVL), which emits yellow light at 577 nm and green light at 511 nm, delivered through a fiberoptic cable. Unlike the PDL, there is no purpura because of the longer pulse duration. However, a long warm up time and short laser cavity life make the CVL a less popular choice than the PDL for vascular lesions.

Diode Lasers: Diode lasers are solid state devices similar in construction to LED's. The familiar "laser pointers" are in fact diode lasers. Diode lasers used clinically emit near-infrared light in the 800-900 nm range. Currently their prinicipal application is in millisecond-range pulsed mode for laser hair removal, and for periodontal surgery. Other applications include treatment of leg and facial veins. Diode bars are also used to excite or "pump" more traditional laser media, for example YAG rods. Because of their relative simplicity and low maintenance requirements, Diode lasers and diode-pumped solid state lasers will be used more in the near future as more wavelengths become available.

Excimer Lasers: Noble gas:Halide, or Excimer Lasers, emit invisible ultraviolet (UV) light that triggers a photochemical reaction on the target tissue. This very short wavelength is capable of high resolution and microscopic surgery-note the letters etched into the human hair at right. The most common medical application is the Argon:Fluorine (Ar:F) laser at 193 nm, used for PRK and LASIK (Laser in-situ Keratomilieusis) vision correction. The laser beam is delivered through an operating microscope integrated with the the laser housing and operating table. Excimer laser radiation shows great promise for cardiac revascularization and lithotripsy, but is currently limited by the lack of durable UV-capable fiberoptic delivery devices.

Intensed Pulse Light: Although not a laser, Intense Pulsed Light (IPL) is currently being used to treat a variety of skin conditions including tattoos, telangiectasia (spider veins), leg veins, as well as for hair removal. Basically, the device is a flashlamp attached to a power source. Pulses of broadband light are applied through colored filters which can be adjusted to match the patient's skin type and the target lesion. Cost of the devices (and of the procedures!) is similar to that of comparable lasers. Although fast and versatile, IPL devices are as a rule less effective at a given task than a laser dedicated to the purpose.

As a photonic "Swiss Army Knife", Intensed Pulsed light (IPL) devices have become very popular over the recent past. They are much less costly to manufacture than lasers-they're basically a pulsed laser without the costly laser components such as the laser rod, pump chamber, optics, and delivery device. Broadband light has the ability to target multiple chromophores, including blood and melanin, and although cutoff filters can modify the emitted broadband spectrum to some extent, it cannot match the specificity of monochromatic laser light. Any photons not absorbed by the target chromophore will be absorbed by other chromophores and then dissipated as heat. This "collateral damage" has actually been touted as an advantage of IPL over lasers by some proponents, but in reality the amount of energy delivered to the intended target may be compromised by undesireable effects on adjacent structures.

IPL devices have been agressively marketed to physicians as a less expensive, "one box" alternative to multiple dedicated lasers. In addition to versatility, IPL devices have the advantage of larger spot sizes than lasers, which is useful for treating large areas quickly. Their lack of specificity limits their use, especially in darker skinned patients. As a rule IPL devices are less effective than a dedicated laser for a given task.

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