Steve measured an apparent power drop in the 2W NPRO output from 2.1W to 1.6W(elog entry no 3698) at 2.1A of diode current in the laser (elog entry: 2822). It was later noticed that the laser temperature was set to about 45 degC while the initial calibration was done at 25 deg C.
It was felt that the recent power drop may have something to do with the increase in the operating temperature of the laser from 25 to 45 deg C. Therefore the laser was returned to 25 deg C and the power output was remeasured and found to be 2.1W as it was at the begining(elog entry:3709)
It was also noticed that returning the laser to 25 deg. C resulted in a loss of efficiency in coupling to the PMC. We suspected that this might be due to multimode operating conditions in the laser at particular operating temperatures. In order to see if this is indeed the case the laser power output was observed as a function of temperature. We do notice a characteristic saw-tooth shape which might indicate multimode operation between 39 and 43 deg C. It is best to verify this by observing the power fluctuations in the transmitted beam of the stabilised reference cavity.
The measurement was made by attenuating the roughly 2W laser beam by a stack of two Neutral Density filfers and then measuring the transmitted light with the PDA36A photodetector. This was because both the power meters used in the past were found to have linear drifts in excess of 30% and fluctuations at the 10% level.