Shedding a Light on Lasers

Since the first ruby laser was put into operation in 1960, laser applications have found their way into all aspects of today’s technology-filled world. Lasers are used from manufacturing and scientific research to military applications, consumer electronics such as CD and DVD players, and the medical industry.

Laser, an acronym for light amplification by stimulated emission of radiation, is usually what we refer to as monochromatic light or coherent light. This light is of one color by having a specific wavelength. This, of course, is not true for all lasers, but for our discussion here we will refer to lasers as monochromatic.

The many types of lasers get their name from the lasing medium used to produce the light photon, such as Argon or CO₂. Lasers produce photons when the lasing medium is excited to a level in which electrons are forced off orbital shells of the atoms of the lasing material. When an electron falls back into the orbital shell a photon is produced, much like x-ray production in x-ray tubes. Lasers have a cavity that holds the lasing material with mirrors at each end; this cavity is referred to as a resonator. The excitation forces electrons off their orbital shell of the atom, and the mirrors force the photons to resonate through the lasing medium, which produces a cascading effect of the photons. The mirror at one end of the laser is “half-silvered,” meaning it reflects some light and lets some light pass. The light that makes it through is the laser light, which is produced by the process called stimulated emission. This is a simplistic explanation of how laser light is produced, but it should give you an idea of how the light is created.

Lasers are operated in two basic configurations or modes: CW, or continuous wave, and pulsed systems. Pulsed systems are referred to as Q-switched, mode locked, or quasi-continuous wave. Pulsed laser systems with a beam output period above .25 seconds are considered CW, according to ANSI Z136.3. Some pulsed-type lasers may have a pulse time of 10s of picoseconds to 10 femtoseconds, or one millionth of a nanosecond, or a quadrillonth of a second—now that is fast.

Many types of lasers have developed over the decades, such as gas, chemical, dye, metal vapor, solid state, semiconductor, and others. Some of the more common types found in the medical community are Helium-neon with a wavelength of 632.8 nm, which is used as an aiming beam for other lasers that are not visible to the human eye. Alignment of these two beams is extremely critical for proper operation. CO₂ lasers with a wavelength of 10.6 µm are widely used in medical procedures, and you can always tell it is a CO₂ unit by the articulating arm. The articulating arm has mirrors in it to direct the beam to the handpiece. Other medical lasers may use glass fibers or flexible quartz as beam-administering devices.

Other medical lasers include the eximer laser (193 nm), used in LASIK surgery; dye lasers (390 to 435 nm), used for birthmark removal; copper vapor (510.6 nm), used in other dermatology applications; and Nd:YAG (1.064 µm), which is one of the most widely used high power lasers. It is usually pulsed down to a nanosecond on time and is a diode laser. Er:YAG (2.94 µm) is also a diode laser and is primarily used in dentistry. The Holmium YAG (2.1 µm) is used for kidney stone removal, tissue ablation, and other medical uses.

Laser-protective eyewear should provide protection against the specific laser wavelength used.

Classifications

The FDA requires all lasers to be classified by the output power of the device—usually stated in watts. Classifications range from Class 1, which is the lowest-power laser that is not considered capable of producing harmful radiation, to the highest level that is designated as a Class 4 laser. Between these two extremes are the classifications of Class 1M, 2, 2M, 3R, and 3B.

Many laser guidelines for safety and power outputs can be found in ANSI Z136 standards. Several Z136 standards are highlighted below:

• Use laser-protective eyewear that provides adequate protection against the specific laser wavelengths being used. All laser eyewear must be marked with optical density (OD) and laser wavelength;
• Display warning signs conspicuously on all doors entering the laser treatment controlled area (LTCA) to warn those entering the area of laser use. Warning signs should be covered or removed when the laser is not in use;
• Maintenance on lasers and laser systems must be performed only by facility-authorized technicians trained in laser service;
• Provide local exhaust ventilation with a smoke evacuator or a suction system with an inline filter to reduce laser-generated airborne contaminants (LGAC) levels in laser applications;
• Use an appropriate filter or barrier that reduces any transmitted laser radiation to levels below the applicable maximum permissible exposure (MPE ) level, for all facility windows (exterior or interior) or entryways located within the nominal hazard zone (NHZ) of a Class 3B and Class 4 laser system;
• Ensure that alignment and calibration techniques are used for routine peri- operative checkout of the laser system;
• Use skin protection if repeated exposures are anticipated at exposure levels at or near the applicable MPE limits for the skin;
• Provide detailed training on laser safety for health care personnel using or working in the presence of Class 3B and Class 4 laser systems; and
• Ensure credentialing of staff using laser systems.

ANSI provides many guidelines for the safe usage of lasers in medical facilities. The Joint Commission has adopted these safety guidelines and also makes a provision for a laser safety officer (LSO) in medical facilities. If the facility does not designate an official LSO, the facility’s safety committee should ensure compliance with FDA and ANSI standards for the safe operation of lasers.

When preparing for the ICC exam, make sure you know what the radiation signs look like and the classifications of lasers. Be mindful of the duties of the LSO, such as training guidelines and ensuring only qualified personnel service and operate the equipment. The other big safety issue with lasers is eye protection for the operator, patient, and other staff who may be in the location of the laser during operation.

Read past ICC Prep and CCE Prep articles in the archives.

Possible laser questions may relate to the OD of the lens. The higher the OD, the less light that can be transmitted through the lens. As an example, an OD of 6 allows 1 millionth of the original light to be transmitted through the filter lens. A high level of protection is often needed because of the power of the laser as well as the human eye’s ability to further focus the power of the beam on the retina. The human eye can focus light on the retina up to 100,000 times. Fortunately, the eye has a self-defense mechanism—the blink or aversion response. When a bright light hits the eye it tends to blink or turn away from the light source (aversion). The human eye aversion time is .25 seconds. This may defend the eye from damage when very low power lasers are involved but cannot help where higher-power lasers are concerned, which is why protective lenses must be worn. With high power lasers, by the time the eye reacts the damage is already done to the retina, which contains the photosensitive cells called rods and cones.

Typical exam questions may include different laser wavelengths, output problems that would encompass optic alignment and problems with glass fiber or quartz cables, and the type of medical application for the laser. I would also encourage anyone taking the exam to review the anatomy and physiology of the eye and know the path of light within the eye. Best of luck!

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John Noblitt, MAEd, CBET, is the BMET program director at Caldwell Community College and Technical Institute, Hudson, NC. For more information, contact .