By: Nate Curtis, Bio-Medical Electronics Student, Western Technical College, La Crosse, WI, 10-16-08
Lasers are used by medical professionals on a daily basis. In this article I will discuss what a laser is, tell you how laser light differs from normal light, I will also go into the different types of lasers, and finally I will discuss the Ellex Super Q laser.
A laser is a device that control the way that energized atoms release photons. “Laser” is an acronym for light amplification by stimulated emission of radiation, which describes very briefly how a laser works. Although there are many types of lasers, all have certain essential features. In a laser, the lasing medium is “pumped” to get the atoms into an excited state. Typically, very intense flashes of light or electrical discharges pump the lasing medium and create a large collection of excited-state atoms (atoms with higher-energy electrons). It is necessary to have a large collection of atoms in the excited state for the laser to work efficiently. In general, the atoms are excited to a level that is two or three levels above the ground state. This increases the degree of population inversion. The population inversion is the number of atoms in the excited state versus the number in ground state. Once the lasing medium is pumped, it contains a collection of atoms with some electrons sitting in excited levels. The excited electrons have energies greater than the more relaxed electrons. Just as the electron absorbed some amount of energy to reach this excited level, it can also release this energy. The electron can simply relax, and in turn rid itself of some energy. This emitted energy comes in the form of photons (light energy).
Laser light is very different from normal light. Laser light has three properties. First, the light released is monochromatic. It contains one specific wavelength of light (one specific color). The wavelength of light is determined by the amount of energy released when the electron drops to a lower orbit. The second property, of laser light, is the light released is coherent. This means that all of the photons have wave fronts that launch in unison. The third and final property, of laser light, is that the light is very directional. A laser light has a very tight beam and is very strong and concentrated. A flashlight, on the other hand, releases light in many directions, and light is very weak and disperses. To make these three properties occur takes something called stimulated emission. This does not occur in you ordinary flashlight. In a flashlight, all of the atoms release their photons randomly. In stimulated emission, photon emission is organized. The other key to a laser is a pair of mirrors, one at each end of the lasing medium. Photons, with a very specific wavelength and phase, reflect off the mirrors to travel back and forth through the lasing medium. In the process, they stimulate other electrons to make the downward energy jump and can cause the emission of more photons of the same wavelength and phase. A cascade effect occurs, and soon we have propagated many photons of the same wavelength and phase. The mirror at one end of the laser is “half-silvered,” meaning it reflects some light and lets some light through. The light that makes it through is laser light.
There are many different types of lasers. Lasers are commonly designated by the type of lasing material, or medium, employed. Common laser types are gas, excimer, dye, semiconductor, and solid-state. Gas lasers, helium and helium-neon, HeNe, are the most common gas lasers, have a primary output of visible red light. CO2 lasers emit energy in the far-infrared, and are used for cutting hard materials. Excimer lasers, the name is derived from the terms excited and dimers, use reactive gases, such as chlorine and fluorine, mixed with inert gases such as argon, krypton or xenon. When electrically stimulated, a pseudo molecule (dimer) is produced. When lased, the dimer produces light in the ultraviolet range. Dye lasers use complex organic dyes, such as rhodamine 6G, in liquid solution or suspension as lasing media. They are tunable over a broad range of wavelengths. Semiconductor lasers, sometimes called diode lasers, are not solid-state lasers. These electronic devices are generally very small and use low power. They may be built into larger arrays, such as the writing source in some laser printers or CD players. Solid-state lasers have lasing material distributed in a solid matrix, such as the ruby or yttrium-aluminum garnet “Yag” lasers. The original laser invented in 1960 was a solid state laser. It used a synthetic ruby rod with mirrors on both ends pumped with a helical xenon flash lamp surrounding rod.
The Ellex Super Q is a YAG laser used by ophthalmic clinics. The Super Q laser is intended to be used for dissection of the posterior capsule of the eye (posterior capsulotomy), dissection of the papillary membrane of the eye (posterior membranectomy), as well as other surgical procedures such as iridotomy (opening a hole in the iris). The procedures are used to treat patients suffering from cataracts and glaucoma. The Ellex Super Q has three main advantages, in using laser light, over other sources to perform the procedures. One is laser light provides significantly higher power densities at the target tissue. The next advantage is the ability to match the wavelength to the absorption properties of the tissue of interest for a desired effect. The final advantage of laser light is the ease of focusing a parallel beam to a small spot size. The Ellex Super Q is aimed by means of a visible red diode laser beam. The treatment beam has a wavelength of 1064 nm and a pulse time of 4ns. The Super Q can be set to pulse from one to three times per firing, depending on the treatment needed. The Ellex Super Q has been designed to provide trouble-free operation with a minimum of down time. As a result very little user maintenance is required. The following routine maintenance procedures need to be completed every six months: cleaning the external optics, checking aiming accuracy, checking optical alignment, and checking the energy monitor.
In conclusion lasers have been around for almost 50 years and are very important to our everyday lives. Laser mediums can range from solid, gas, liquid, or semiconductor. YAG lasers are solid-state lasers that use yttrium-aluminum garnet as its’ medium. Lasers can have very little power, such as the ones used in laser printers or CD players, or they can be very powerful, such as C02 lasers used to cut through hard materials. Lasers are very common on the medical field because of their accuracy and high power densities on target areas. YAG lasers are used regularly in ophthalmology, cosmetic medicine, and dentistry. As laser and medical technology moves forward there is no limit on what can and will be done with lasers in the medical field.
Abbott Medical Optics
MEL 80 excimer laser, Carl Zeiss Meditec
S2, S3, S4, S4IR excimer laser, Abbott Medical Optics
Second Source Parts
Second Source Service
1. Laserex SuperQ Installation, Commissioning,and Service Manual. Laserex Systems Inc. 2006. 1-232.
2. Matthew, Weschler. "How Lasers Work." How Stuff Works. Florida State University. 16 Mar. 2008 <http://www.howstuffworks.com/>.
3. "Nd: YAG Laser." Wikipedia. 28 Feb. 2008. 16 Mar. 2008 <http://en.wikipedia.org/wiki/Main_Page>.