The output power of the front end seems to have a ~20 minute oscillation in it.  Seems to
coincide with crystal temperature fluctuations.  The crystal fluctuations however do not
coincide with the flow rate.  I cannot determine if it is due to fluctuations in the crystal
chiller flow rate because we do not have enough resolution but the crystal chiller flow rate
appears to be constant.

The fluctuations do not seem to coincide with humidity either.  Nor room temperature.
Possibly fluctuations in the NPRO output power (FrontEndPowerOscillation6.png), it is
hard to tell.  There seems to be a small coincidence with the NPRO second pump diode
(FrontEndPowerNPROD2.png).  There does not appear to coincidence with any of the other 
NPRO signals monitored.

I should mention that the laser power mentioned here is prior to the power stabilisation
sensing.  The same fluctuation is not apparent in the reflected signal from the pre-modecleaner.