With the most recent Nufern amp (July 2012) the gain was measured with The Rock as an input source (~150mW).
Previously the gain was seen to be very sensitive to the temperature of the cooling water (the pump diodes are water cooled and so their wavelength may move around). The above measurements were taken with 21 degree Celsius cooling water. The Nufern is typically run at 70% power which has been observed to increase stability.
Fluctuations in the output power of the Nufern are typically observed, and have been linked to a variation in the lineal polarization direction of the beam. After a polarizing element this is translated into a power fluctuation, which was observed to stabilize after a 30 minute warm up period. The fluctuations are plotted below with the Nufern running at 70% output power: