Chapter 8

Principles of Laser Radiation Safety

8.1 Laser Radiation Safety for Non-technical Staff

Non-technical staff should read Sections 8.2 and 8.3 of this chapter to get a feeling for what hazards may exist in labs using lasers. Again, the basic laser radiation safety principle for non-technical staff is a simple one: avoid going into labs that bear the universal laser-radiation hazard sign, shown at right.

If you must go into a laser lab, make sure that a qualified technical staff member or student is present in the lab with you so that you do not suffer accidental exposure to either laser radiation or to associated toxic chemicals. Take note: looking into a laser lab and seeing no laser radiation does not mean that no lasers are on. Some lasers emit in the invisible light region and can be quite hazardous. For example, carbon dioxide lasers (which is a certain type of laser) are used to cut thick steel plate (imagine what such a beam would do to your eyeballs or other valuable body parts), and yet its radiation is completely invisible. Several such lasers are routinely used within the Department.

8.2 Primary Health Dangers due to Lasers

  1. Damage of the retina or other eye tissue from direct laser beams;
  2. Damage of skin tissue (burns) from direct exposure to laser beams (At left is shown a laser which is able to ignite a piece of paper!);
  3. Toxicity of various chemicals commonly encountered in laser systems, such as carcinogenic dyes in pumped dye lasers, or extremely toxic gases such as fluorine, used in excimer lasers;
  4. Electrocution by the high-voltage power supplies required by many lasers.

Just as there are a wide variety of types and activities for radioactive sources, so are there a wide variety of types and power levels for lasers. Safety precautions that are absolutely mandatory for some types of lasers may not be needed at all for other lasers. For example, it is obvious that the dangers present in a 100 W CO2 laser are far greater than in a 1 mW HeNe laser. (Not only is 100 W >> 1 mW, but also the CO2 emission, at 10.6 microns, is invisible.) It is your responsibility to learn exactly what the meaningful hazards are for the laser system that you will be using and to protect against them.

8.3 General Precautions

Never look directly into the beam or at specular reflections of the beam. Be especially careful when the beam energy density exceeds the permissible exposure levels (see below). If possible, work with lasers in a well-lit environment; this will keep your pupils constricted, thus minimizing the total coherent energy which may enter your eyes.

For high-power lasers, or for lasers that emit in the damaging UV region, or for lasers whose emission is invisible, it is essential that the appropriate safety glasses be worn. These glasses are made of filters of varying optical densities that absorb radiation in a specific wavelength band. Make sure that the safety filters that you wear are rated for the beam intensity of your laser, and that the absorption wavelength of the filter matches that of your laser!

Make sure that the path of your laser beam is such that it will not be accidentally encountered by persons in your lab. Always terminate the laser beam with an appropriate target, one that is neither reflective nor potentially flammable. Try to avoid working with the laser beam at eye level (either standing or sitting).

Always be vigilant around high-voltage power supplies for lasers! Tragically, graduate students have died by electrocution from the high voltage that is present in many laser systems. If voltages above 15 kV are used, ensure that your exposure to potential x-ray emission is negligible.

Some lasers, such as pumped dye lasers and excimer lasers, require toxic liquids and gases for their operation. These can be quite dangerous, and you should be familiar with their risks before you use the laser. MSDS sheets should be available to you for each potentially toxic substance that you use, and you should read them. If laser dyes are dissolved in toxic solvents, the spent solutions must be disposed of as hazardous wastes. hazardous waste disposal procedures are given in chapter 4.

For high-power lasers, protective gloves and clothing may be required so that you do not suffer accidental burns.

8.4 Some Exposure Guidelines

We cannot give maximum exposure levels for all frequencies of laser radiation.

Instead, to give you an idea of typical guidelines, we list the maximum permissible exposure levels for laser radiation at the cornea for direct illumination or specular reflection at a wavelength of 694.3 nm (taken from Ref. 1):

( For Q-switched 1 nsec to Continuous wave CW)
Conditions msec pulse (J/cm2) exposure (W/cm2)
Daylight (3 mm pupil) 5.0*10-8 5.0*10-5
Laboratory (5 mm pupil) 2.0*10-8 2.0*10-5
Night (7 mm pupil) 1.0*10-8 1.0*10-5

For example, radiation at 694.3 nm is not as hazardous as radiation from an Ar ion laser, so the above levels should not be applied to all types of lasers.

8.5 References

1. J. F. Ready, "Effects of High-Power Laser Radiation" (Academic Press, 1971).

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