Even low power laser beams can be hazardous to the human eye.
The more sensitive a detector is, the more delicate it is. The human eye is still far and away the ultimate photonic detector – and it doesn’t take much to damage it, even with its built-in safety mechanisms (such as the blink reflex).
There are CDRH standards that define laser safety categories in terms of risk to humans. These standards also define test setups so that such safety categories are objective and can be universally understood and applied.
Ophir offers power sensor accessories for those involved in such measurements. These include apertures of 7mm diameter (the “standard” pupil diameter in darkness) and 3.5mm (the “standard” pupil diameter in daylight) for use with Ophir’s “PD300” family of photodiode sensors.