From: jeedom74000@gmail.com   
      
   Greetings Phil and many thanks for your reply.   
      
   I will experiment with wiring the detectors in series between op   
   osite-polarity bias supplies, seems like a simple and sound setup, just what I   
   needed :)   
       
   My application is about stabilizing long exposures of holography setups;   
   nothing new but I like to revisit things by myself.   
      
   From what I understand now:   
      
   - the single detector approach has the advantages of not requiring a specific   
   fringe spacing and enabling simple phase stepping the interferometer (by   
   inserting a bias voltage in the loop) but has the disadvantage of requiring   
   fringe contrast calibration    
   and is prone to error if the laser output power varies.    
   Here is a nice article on that setup: https://www.researchgate.n   
   t/publication/263582518_A_Laser_Interferometer_for_the_Undergrad   
   ate_Teaching_Laboratory_Demonstrating_Picometer_Sesitivity   
      
   - the two detector approach is immune to laser output power fluctuations but   
   requires proper fringe spacing   
      
   In both cases I don't quite see why it is much more complicated to introduce a   
   (low frequency) carrier frequency in the optical setup by means of an   
   additional mirror on a transducer in order to improve the "reactivity" of the   
   loop to some external    
   vibration as suggested above but I might be missing something.   
      
   Best regards   
   Loic   
      
   PS: if anyone is interested in holography here is a link to my channel on what   
   I do in holography (purely amateur, nothing to sell):   
   https://www.youtube.com/@hololab7368/videos   
      
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