LASER SAFETY

LASER SAFETY
INTRODUCTION
Lasers have become increasingly important research tools in Medicine, Physics, Chemistry,
Geology, Biology and Engineering. If improperly used or controlled, lasers can produce injuries
(including burns, blindness, or electrocution) to operators and other personnel, including
uninitiated visitors to laboratories, and cause significant damage to property. Individual users of
all lasers must be adequately trained to ensure full understanding of the safety practices outlined
in The University of Texas Laser Safety Policy.
The Laser Safety procedures here at the University follow the requirements of the Texas
Department of Health Bureau of Radiation Control, and the guidelines from the American
National Standards Institute (ANSI) as specified in the ANSI Standards Z136.1, “The Safe Use
of Lasers.”
WHAT IS A LASER?
LASER is an acronym that stands for Light Amplification by Stimulated Emission of Radiation.
The energy generated by the laser is in or near the optical portion of the electromagnetic
spectrum. Energy is amplified to extremely high intensity by an atomic process called
stimulated emission. The term “radiation” is often misinterpreted because the term is also used
to describe radioactive materials or ionizing radiation. The use of the word in this context,
however, refers to an energy transfer. Energy moves from one location to another by
conduction, convection, and radiation. The color of laser light is normally expressed in terms of
the laser’s wavelength. The most common unit used in expressing a laser’s wavelength is a
nanometer (nm). There are one billion nanometers in one meter (1 nm = 1 X 10-9 m). Laser light
is nonionizing and includes ultra-violet (100-400nm), visible (400-700nm), and infrared (700nm-
1mm).
ELECTROMAGNETIC SPECTRUM
Every electromagnetic wave exhibits a unique frequency, and wavelength associated with that
frequency. Just as red light has its own distinct frequency and wavelength, so do all the other
colors. Orange, yellow, green, and blue each exhibit unique frequencies and wavelengths.
While we can perceive these electromagnetic waves in their corresponding colors, we cannot see
the rest of the electromagnetic spectrum.
Most of the electromagnetic spectrum is invisible, and exhibits frequencies that traverse its entire
breadth. Exhibiting the highest frequencies are gamma rays, x-rays and ultraviolet light.
Infrared radiation, microwaves, and radio waves occupy the lower frequencies of the spectrum.
Visible light falls within a very narrow range in between.
LASER HAZARDS
BEAM HAZARDS
The laser produces an intense, highly directional beam of light. If directed, reflected, or focused
upon an object, laser light will be partially absorbed, raising the temperature of the surface
and/or the interior of the object, potentially causing an alteration or deformation of the material.
These properties which have been applied to laser surgery and materials processing can also
cause tissue damage.
In addition to these obvious thermal effects upon tissue, there can also be photochemical effects
when the wavelength of the laser radiation is sufficiently short, i.e., in the ultraviolet or blue
region of the spectrum. Today, most high-power lasers are designed to minimize access to laser
radiation during normal operation. Lower-power lasers may emit levels of laser light that are not
a hazard.
The human body is vulnerable to the output of certain lasers, and under certain circumstances,
exposure can result in damage to the eye and skin. Research relating to injury thresholds of the
eye and skin has been performed in order to understand the biological hazards of laser radiation.
It is now widely accepted that the human eye is more vulnerable to injury than human skin. The
cornea (the clear, outer front surface of the eye’s optics), unlike the skin, does not have an
external layer of dead cells to protect it from the environment. In the far-ultraviolet regions of the
optical spectrum, the cornea absorbs the laser energy and may be damaged. At certain
wavelength in the near-ultraviolet region and in the near-infrared region, the lens of the eye may
be vulnerable to injury. Of greatest concern, however, is laser exposure in the retinal hazard
region of the optical spectrum, approximately 400 nm (violet light) to 1400 nm (near-infrared)
and including the entire visible portion of the optical spectrum. Within this spectral region
collimated laser rays are brought to focus on a very tiny spot on the retina. In order for the worst
case exposure to occur, an individual’s eye must be focused at a distance and a direct beam or
specular (mirror-like) reflection must enter the eye. The light entering the eye from a collimated
beam in the retinal hazard region is concentrated by a factor of 100,000 times when it strikes the
retina.
Therefore, a visible, 10 milliwatt/cm2 laser beam would result in a 1000 watt/cm2 exposure to the
retina, which is more than enough power density (irradiance) to cause damage. If the eye is not
focused at a distance or if the beam is reflected from a diffuse surface (not mirror-like), much
higher levels of laser radiation would be necessary to cause injury. Since this ocular focusing
effect does not apply to the skin, the skin is far less vulnerable to injury from these wavelengths.
NON-BEAM HAZARDS
In addition to the direct hazards to the eye and skin from the laser beam itself, it is also important
to address other hazards associated with the use of lasers. These non-beam hazards, in some
causes, can be life threatening, e.g. electrocution, fire, and asphyxiation. The only fatalities from
lasers have been caused by non-beam hazards.