Second case

While adjusting an experiment involving a class 4 Titanium-doped Sapphire laser oscillator, a PhD student got briefly exposed to the beam.

In order to facilitate the alignment procedure by directly observing the beam with the naked eye – instead of a more complicated procedure implying a camera or an infrared sensor, the student worked in continuous mode at full power (700 mW), in the dark, without safety goggles.

As he had to elevate the beam to the same height as the rest of the experiment, he first adjusted a periscope with the two mirrors as close as possible, and tightly fixed the bottom mirror – sending the beam to the ceiling. On the contrary, as he knew he would still have to move the upper mirror, he didn't tightly fix it. During the adjustment procedure, the student bent over the desk, thus placing his eye precisely over the periscope. His hand accidentally ran into it, the upper mirror moved away from the beam, which briefly entered the student's eye. The retina was damaged, nervous cells of the macula were burnt. This lead to a permanent and irreversible trouble of his sight angle without loss of visual acuteness.

This accident could have been avoided if the following precautions had been applied:

• The student should have been wearing his safety goggles adapted to the pulsed laser, which were placed next to him.

• While working with a laser, the ambient light must always be over a certain level, in order to prevent the pupil from getting wide opened.

• Always work at minimum power when adjusting an optical system.

• In order to trace the trajectory of the beam, always use a camera or a visualization card which transforms the invisible beam into a visible spot.

• Always tightly fix the optical elements, even if their positions must be optimized later.