Proper laser eyewear is required whenever a laser is operated in the open. “Open” means the laser beam is exposed and could make contact with humans nearby. Even at low power, lasers can cause serious eye damage. The laser safety officer will determine what type of laser eyewear is required to protect those that need to be near the exposed laser beam. Any facility that uses lasers should have someone that has had laser safety officer training such as that provided by Rockwell Laser Industries.
Two terms (of several) used to describe contact of the laser beam with the human eye are intrabeam and diffuse reflection. Intrabeam is when the collimated (non-spreading) beam from the laser makes direct contact with the human eye. The second term is called a diffuse reflection. A diffuse reflection is when the laser beam reflects off of a non-mirror-like surface. A diffuse reflection can still cause permanent eye damage.
Figure 1 below shows a pair of clear plastic safety glasses. A photocopied eye on paper has been placed behind the clear plastic lens. The red targeting laser from a 1kW fiber laser is on showing where the fiber laser beam will impact the target. The fiber laser has a wavelength of 1070-nm. This wavelength is not visible to human eyes and will pass through the clear plastic safety glasses. The video shows a short 1000-watt pulse from the laser onto the clear safety glasses and shows the horrific results.
Figure 2 shows a pair of proper laser eyewear. A similar paper eye has been placed behind its lens. In this situation, the collimated laser beam first reflects off of a piece of aluminum onto the eye. This is a “diffuse reflection”. The same 1000-watt laser pulse is used. The video shows the laser beam reflects off of the aluminum onto the laser eyewear where the laser eyewear prevents the laser beam from damaging the paper eye target.