I checked the noise on the pd of the 1310nm probe laser. with and without sample. then I tried to switch off the chopper, to switch off the pump and to put the PD in the crossing point where the waist of the probe is inside the size of the detector. In all the cases the noise is around 100 uV. This means that the noise comes from the laser. So we are planning to make a power stabilization control loop on the laser.

Details and plots of the noise follow:

note that in the case of LMA sample with power=960mW, the SNR is about 1

with lma#15033 sample at the crossing point:
laser current 400mA; OD2 filter
pump on 960mW; chopper on
filename: lma15033crossing_point.txt

with lma#15033 sample at the crossing point:
laser current 400mA; OD2 filter
pump on 34mW; chopper on
filename: lma15033crossing_point-2.txt

with lma#15033 sample at the crossing point:
laser current 400mA; OD2 filter
pump off; chopper on
filename:  lma15033crossing_point-3.txt

with lma#15033 sample at the crossing point:
laser current 400mA; OD2 filter
pump off; chopper off 
filename: lma15033crossing_point_internal1kHz.txt

with lma#15033 sample at the crossing point:
laser current 400mA; OD2 filter
pump off; chopper off
filename: lma15033crossing_point_internal380Hz.txt

no sample
laser current 300mA; OD2 filter
pump off; chopper off
filename: 1310nmno_sample_no_chopper_internal380Hz