Often, welding operations such as MIG and TIG will be occurring in the presence of your laser shaft alignment system. The question often comes up: will this light energy damage the optics? The answer is no.
However, if you must weld in the presence of your laser alignment system, a greater source of damage could be from the heat, sparks, and electrical energy that is emitted from the process. We do not recommend leaving equipment attached to anything being welded due to these dangers. Welding is like having a continuous lightning strike occur and electrical voltage differences and resulting magnetic fields could cause electrical damage. Remove your equipment to protect it from such hazards.
As far as light energy goes, OSHA has standards for minimum eye protective shade numbers ranging from “4” for gas welding to “11” for shield metal arc welding and finally up to “14” for carbon arc welding processes. NASA recommends a number “14” for directly viewing solar eclipses. All of this is for protecting the human eye, which is less resistant to damage from light than a laser detector. A laser detector is designed to continuously absorb direct laser light energy over a continuous period of time. This is far more light energy than the human eye would encounter from arcs and sunlight with proper protective gear. Warning labels caution you not to stare directly into the laser beam!
Many laser alignment systems have special protective coating on the detector that is optimized for the specific laser wavelength of light it is intended to detect. This helps prevent interference from the bright sun causing measurement error. Many laser systems are used in bright sunlight, and some work better than others under such conditions. Since the welding energy would at most be of the same intensity as direct sunlight, this would most likely not cause damage. Of course, you could also put the protective caps on to be completely safe.