how much the laser power drops in 50m,100m,200m ?

There is a constant ?

depends on air quality? weather? humidity?



Thanks for the attention.

All of the things you mentioned contribute to loss in power.
Also, power density decreases according to the inverse square law. There was a discussion about this but I can't find the thread.

Divergence is going to kill your power density faster than anything else you list. As the beam expands, the area the power is spread over increases even though the actual power there is pretty much the same.

100mW at 50 yards hitting a target would still be fairly close to 100mW, it will just look dimmer because the power would be spread out over a wider area.