Here is a total shot in the dark.
The lasing medium needs a certain amount of energy to reach the "lasing" excitation level and you may be giving it enough energy to get some of the particles up to that level and over time (milliseconds or less ) enough hit that level to give out a burst of light. Then the system has to build up again.
Basically your not getting enough power to the laser at that low power level.
just a guess based off of very little info and a lot of reading on lasers.
thanks
Michael T.
"If you don't stand for something, chances are, you'll fall for anything!"