The high power lasers I tested so far (the Thorlabs 21mW and the JDSU 1125P) are noisy: they both have wandering lines that from time to time are alised down into the base band, destroing the measurement. 

I have three JDSU 1103P units: two of them dlived about 2.5 mW, the third one delivers about 1.4 mW. One of the 2.5mW was installed in the test setup. I swapped it out with the 1.4 mW, so now I have two good 2.5 mW laser. My plan is to modify the new setup to use those two lasers in parallel, splitting each one in two, for a total of four beams of about 1.2 mW each.

The new optical layout is atttached.