Which subclass of lasers are intermediate-power visible lasers, but are potentially hazardous in less than 0.25 seconds if viewed with collecting optics?

• A. Class 3R
• B. Class 2
• C. Class 2M
• D. Class 4

Answer: (C)

The concept here is that some visible lasers are safe to view with the naked eye most of the time, but can become hazardous when their beam is viewed through collecting optics. The “M” suffix signals this additional hazard: the beam is concentrated by lenses or magnifiers, which can dramatically increase retinal irradiance in a very short time.

In this case, the laser is described as intermediate-power and visible, with the caveat that it can be hazardous in less than a quarter of a second if you look at it through collecting optics. That combination points to a 2M classification: normally safe to look at directly due to the blink reflex, but dangerous when viewed with magnifying optics because the light is concentrated. The other options don’t match this specific scenario—the higher-power classes imply broader hazards, and the plain 2 class doesn’t address the collecting optics risk.