For those involved in research and development, laser safety is a real concern. Users access energized components and manipulate beams, therefore the potential for a stray reflection is always present; or users may work with homemade components or commonly split beams and change the plane of the beam. Put this all together with the lack of engineering controls, and the potential for injury is higher than most users think.
Here are five steps to help reduce the odds of an injury.
1. On the Job Training
While every institution should and does require some fundamental laser safety training, on the job training (OJT) is critical. Effective OJT or mentoring is what is most likely to prevent, as opposed to set up, an accident. The mentor-trainer needs to have the patience to explain the set up, the goal, and problems they have encountered.
The trainer should also explain the sources of known reflections, non-beam hazards, and how to use safety tools such as viewers and eyewear. The trainee needs to be observed doing tasks, even if hired as the expert on the equipment, at the very least to evaluate his or her safety culture. The trainee also needs to feel encouraged to ask questions and receive supportive responses, not body language that discourages any further questions. Both parties need to be in agreement prior to letting new users work unsupervised.
Numerous laser incidents can be traced to poor housekeeping. Laser housekeeping is not the childhood activity of hiding everything under your bed, or now optical table, but rather setting time aside to keep work spaces (optical table and work area) clean. By clean I mean free of unused tools, equipment, reflections sources, cleaning solvents, storage boxes, etc. Granted, space is an ever-present problem, as well as the time to clean, but organization tools such as storage lockers and shelves over the optical table can help.
Setting a dedicated day and time in your schedule to clean is a proven solution; waiting for that open afternoon in your schedule will never happen. Cleaning once a month is good, once a week is better, and the best solution is to incorporate housekeeping into your daily routine. Address problems as they arise. This will make housekeeping a less daunting task.
Your clutter?from things you might need one day to just excess optics on the table?sends a subliminal message to observers and funding sources. The message is: if they work in such a disorganized mess, how good can their science be, and how reliable are their results?
3. Look for Stray Reflections
In reviewing laser accident reports in the research and academic environment, the most common scenario is the lack of eyewear use during laser alignment. A number of these cases involve a failure to look for stray reflections. A 1 mW/cm2 beam in the wavelength range of 400 to 1400 nm equals 100 W/cm2 at the retina. This is about the maximum an eye can tolerate, and the typical 4% reflection off many optics could easily be above the safe threshold.
Remember, the macula/fovea portion of the retina where 400 to 1400 nm light is focused is the critical vision portion of your eye. Hence, as alignment is performed, you need to go optic to optic and check for stray reflections at each. Beam splitters have been involved in several accidents when the user forgot to block the unneeded split.
4. Contain Reflections
Following from step three, if stray reflections are identified or expected, containment or blockage of those reflections is critical to preventing laser accidents. Sometimes it is as simple as placing a card behind or above an optic in a mount.
I have encountered incidents where users have a known reflection that seems likely no one will be in front of, because the angle is too steep or the power is too low to cause injury. In each case, a circumstance arose that placed someone in danger, or the output was higher than believed. Beam blocks, perimeter guards, table enclosures, and beam dumps all add to your safety and those around you?use them!
Lastly, I would be banished from the U.S. laser safety community if I did not mention laser protective eyewear. It is fitting that eyewear be mentioned last, as they are not your first line of defense, but rather your last. The four steps above provide the real safety. Laser eyewear is like a seat belt: if all road rules and conditions are followed, it will never be needed, but if any fail, it might save your life. There are two types of eyewear:
Full protection: This has a sufficiently high optical density to block any direct or stray beams and should always be used with invisible wavelengths. Alignment eyewear: This should be used with visible beams when they need to be seen.
Today with new filters and styles of laser eyewear, one can be found for just about any application.
Ken Barat is the laser safety officer (LSO) at Lawrence Berkeley National Laboratory (Berkeley, CA). He is a former LSO for the National Ignition Facility Directorate, a Laser Institute of America Fellow, an American National Standards Institute (ANSI) member, and chair of the new ANSI Z136.8 committee Laser Safety in R&D and Testing. You can reach Barat at Kbarat@lbl.gov