The output laser power is measured by an thermal detector (Ophir VEGA) at the output fiber end through a Sapphire filter. The filter is a dichroic mirror used to get rid of the pump power at 1.5 microns. 

The incident pump power is measured before the gain fiber by the same thermal detector. The absorbed pump power is the pump power at P(9) line which is absorbed by acetylene. It is calculated by subtracting the measured total on resonant pump power at the output end of fiber from the total on resonant pump power plus the 3 micron laser power.