Surgical Lasers

Most people know of the Matrix movie trilogy. In the first one there is a scene near the end when Neo is fighting Mr. Smith. While he is fighting the agent in the matrix, in real life robot machines, (Squiddy’s), are carving the ship he is on to pieces with lasers. Lasers have been used for many years and provide a myriad of services to us. Lasers can be used to scan barcodes on food in grocery stores, or provide police officers with evidence to throw you under the jail for speeding. Lasers can also be used for delicate surgery. There are several different types of surgical lasers such as YAG lasers, CO2 lasers, and Holmium lasers being the most common ones. Each one is vastly different in what produces the laser light.

YAG lasers are used for cataract surgery and minor eye surgeries. YAG stands for yttrium aluminium garnet which is the material used to dope the lens of the laser. (Yttrium is a rare earth metal with an atomic weight 39) YAG lasers have a shorter wavelength than the more powerful CO2 laser. This means that the YAG laser light is more easily absorbed by water filled human tissue. This makes the laser perfect for applications such as cataract removal. A cataract is a clouding of the area behind the lens of the eye. The Yag laser power level can be adjusted to remove the cataract without damage to the lens. This is possible because the lens is clear and passes the laser light easily to the cloudy cataract behind it. Most YAG lasers use a stepper motor configuration to increase or decrease the power level of the laser. Beam alignment is done through a series of mirrors that are adjusted for angle, tilt, and centering. Because the laser is used in extreme close proximity to the eye a guiding laser beam is usually not necessary. What is a guiding laser beam? Read on.

CO2 lasers are perhaps the most powerful of lasers used in surgery. An 80 watt CO2 laser can literally burn a hole through a 1/4″ thick piece of steel in seconds. These require extreme caution when working around them. This type of laser generally has 2 separate lasers that work as one. The first laser is a Helium Neon or HeNe laser. It is typically very low power such as milliwatts and is generated through a ruby crystal which gives it the bright red light that you can see. The real power is provided by the CO2 laser. Since CO2, (Carbon Dioxide) is a colorless gas it produces no visible beam of light. Carbon Dioxide is not the only gas present in the laser tube there is also Nitrogen, Helium, Hydrogen, and Xenon in varying percentages.

The Helium Neon laser light is adjusted to coincide with the CO2 laser beam. They emerge from the lens in perfect unison when the machine is properly calibrated. The HeNe light is red and visible and gives the surgeon something to see. When he steps on the power switch the CO2 laser is activated and the beam travels along the same path as the HeNe laser and cuts or burns whatever is required. When you see a laser cutting something remember it’s not the red light that is doing the cutting it’s the invisble CO2 that is hitting the same spot. Calibration is a little more difficult because not only does angle, tilt and center have to be calibrated but so does the Near/Far adjustment. The near/far adjustment is to bring the CO2 laser into precise conjunction with the HeNe laser. The near adjustment is usually done first followed by the far adjustment. Next comes the angle, tilt and center alignments. Adjusting most CO2 lasers can be a little time consuming and normally takes about 2 or 3 hours to complete. After adjusting the laser beam the power levels are normally verified and adjusted as well. Unlike the YAG laser which uses stepper motors the majority of CO2 lasers use digital circuits to adjust power.

Last but not least is the Holmium laser. Holmium lasers use the same YAG material for the lens but these lasers are used for a different type of surgery. They are normally used for the removal of kidney and gall bladder stones. These also use a guiding laser but in this case the guiding laser is produced by an emarald crystal which gives it a green colored light. Adjustment is the same as the other two with mirrors and alignment procedures outlined in their service manuals. One other difference worth noting is that Holmium lasers transfer the cutting power through a fiber optic cable into the patients body where precision manipulation by the surgeon can guide the fiber optic tip directly to the needed area. Because of this fiber optic delivery method of the laser power, (usually about 2o watts more or less), an addition of a piece called a blast shield is necessary. The blast shield stops the laser beam from burning through the sheathing of the fiberoptic cable at the point of attachment to the laser.