Lasers

General Precautions

1. Only use the lasers after you have received and understood how to use the equipment safely and properly.
2. Never look into the primary beam of a laser. Avoid looking at specular (mirror-like) reflections of the beam, including those from a lens surface.
3. Never point a laser beam toward another person's eyes.
4. Do not aim lasers by eye. Looking along the axis of a beam increases the hazard of reflections. Lasers should be aimed using diffusely reflecting screens to locate the beam's position Eyes should be kept well above the level of the beam.
5. Keep the level of general illumination high in areas where lasers are being operated. Darkened rooms cause the pupils of the eyes to dilate and thus increase the amount of energy that may inadvertently enter the eye.
6. Since laser beams slowly diverge, working at some distance from the laser increases their safety.
7. Never view a laser directly by any light gathering optical instruments such as telescopes or microscopes.
8. View transmission holograms with a greatly expanded beam. Mount the diverging lens firmly.
9. Report malfunctioning equipment immediately to the instructor or a lab demonstrator.

Eyewear
All persons must wear protective glasses or goggles whenever operational conditions may result in a potential eye hazard, during alignment of undiverged beams, and until beam stops are in place. There are two types of available protective eyewear both of which filters out only the specific wavelength of a laser:

1. Alignment glasses or goggles-These reduce the intensity of the laser light to a safer level so that the beam is visible during alignment procedures.
2. Full protection glasses or goggles- These block out almost all the laser light and can be worn by those who do not have to be able to see the laser beam.

Note that eyewear does not provide broad-spectrum protection or absolute protection against eye injury.

Use of lasers in student and public demonstrations and displays
In unsupervised displays, use only class 1, 2 or 3a lasers. Do not expose spectators to direct or specularly reflected beams and do not allow them to access the laser. Use class 3b lasers for supervised demonstrations only, as long as safe operating procedures are maintained.

Classes of Lasers and their Safety Hazard Rating

CLASS 1 (less than or equal to 0.4 microwatts): Radiation levels are too weak to consider a hazard.

CLASS 2 (greater than 0.4 mW but less than 1 mW): Radiation levels are not generally a hazard, although temporary blind spots can result if the beam enters the eye. General precautions are adequate.

CLASS 3 (greater than Class 2 but less than or equal to 0.5 W): Radiation from this class of laser can cause irreversible eye damage as permanent blind spots and lesions.

Class 3a: Laser pointers and some diode lasers fall into this class. General precautions are adequate but there is the greater potential for eye damage.

Class 3b: Lasers used for holography and other optics experiments fall into this class. Safeguards-key switches, delayed power on, and output aperture shutters-are installed in the laser. Besides the general precautions, the following special ones are required:

1. Warn anyone in the area or who may enter the area that the laser is in use. Post signs as well.
2. Limit entry to the area to only those persons performing an experiment with the laser. Do not allow spectators.
3. Eliminate any potentially hazardous beams with an absorbent nonspecular beam stop, a curtain, or a screen. Mount these beam stops solidly.
4. Where feasible, place only diffusely reflective materials in or near the beam path.

References
1. ANSI Z136.1-1980 -- "Safe Use of Lasers"
2. Teaching Physics Safely, American Association of Physics Teachers, 1979