General Laser Safety

Optical Safety

Because of its special properties, laser light poses safety hazards not associated with light from conventional sources. The safe use of lasers requires that all laser users and everyone else near the laser system are aware of the dangers involved. The safe use of the laser depends upon the user becoming familiar with the instrument and the properties of intense and coherent beams of light.

The greatest concern when using a laser is eye safety. In addition to the main beam, there are often many smaller beams present at various angles near the laser system. These beams are formed by specular reflections of the main beam at polished surfaces such as lenses or beam splitters. While weaker than the main beam, such beams may still be sufficiently intense to cause eye damage.

Laser beams can be powerful enough to burn skin, clothing or paint. They can ignite volatile substances such as alcohol, gasoline, ether and other solvents, and can damage light-sensitive elements in video cameras, photomultipliers and photodiodes. The laser beam can ignite substances in its path, even at some distance. The beam may also cause damage if contacted indirectly from reflective surfaces. For these reasons the user is advised to follow the precautions below.

1. Observe all safety precautions in the Preinstallation and Operator's manuals.
   
2. Extreme caution should be exercised when using solvents in the area of the laser.
   
3. Limit access to the laser to qualified users who are familiar with laser safety practices and who are aware of the dangers involved.
   
4. Never look directly into the laser light source or at scattered laser light from any reflective surface. Never sight down the beam into the source.
   
5. Maintain experimental setups at low heights to prevent inadvertent beam-eye encounter at eye level.
   
6. As a precaution against accidental exposure to the output beam or its reflection, those using the system should wear the appropriate laser safety glasses as designated by the wavelength being generated.
   
7. Avoid direct exposure to the laser light. The intensity of the beam can easily cause fleshes burns or ignite clothing.
   
8. Use the laser in an enclosed room. Laser light will remain collimated over long distances and therefore presents a potential hazard if not confined.
   
9. Post warning signs in the area of the laser beam to alert all laser users and everyone else near the laser system of the hazards specific to the class of laser present.
   
10. Advise everyone using the laser of these precautions. It is good practice to operate the laser in a room with controlled and restricted access.

Electrical Safety

Most, if not all, Class III and Class IV laser systems (see the next section for information relating to classification of laser systems) utilize high-level AC and DC voltages in both the laser head and power supply. All Coherent laser systems are designed for operation with the laser head and power supply covers closed. Only trained personnel aware of the hazards involved should remove the protective covers.

The government recommended safety practices for a given laser system will depend on its classification. The following list highlights the criteria used to classify lasers, as well as listing the key safety considerations when operating a system within the indicated classification. See "Code of Federal Regulations" for a comprehensive discussion of these safety topics.

• Wavelength:
  If the laser is designed to emit multiple wavelengths the classification is based on the most hazardous wavelength.
• Output Characteristics:
  For continuous-wave (CW) or repetitively pulsed lasers the average output power (watts) and limiting exposure time inherent in the design are considered.
• For pulsed lasers the total energy per pulse (joule), pulse duration, pulse repetition frequency and emergent beam radiant exposure are considered.

Laser Classification

• Class I Lasers
  These systems are also classified as "Exempt" lasers. They are normally not hazardous with respect to continuous viewing, or are designed in a way that prevents human access to laser radiation (e.g., laser printers).
• Class II Lasers (Low Risk)
  These lasers emit visible light, which, due to normal human reflex responses, do not present a hazard. However, a safety risk would be posed if the output source were brought to within close proximity of the eye and then viewed for an extended period of time.
• Class III Lasers (Moderate Risk)
  Class III lasers can cause eye injury if viewed momentarily, but are not capable of causing serious skin injury or hazardous diffuse reflections without the use of collecting/conditioning optics (e.g., fiber optics, telescopes, etc.).
• Class IV Lasers (High Risk)
  These lasers present an eye hazard from direct and diffuse reflections. In addition, class IV lasers can cause combustion of flammable materials and produce serious skin burns and injury from direct exposure. Most laser systems manufactured by Coherent fall into this classification.