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Entry   Optical amplifier polarization state, posted by Ronic Chiche at Optical room about lasers and optics Screenshot_2019-12-17_8_122311.pngScreenshot_2019-12-17_7_122157.png
    Reply   Optical amplifier polarization state, posted by Ronic Chiche at Optical room about lasers and optics cavity_polar_2e_etage_1kW.PNG
       Reply   Optical amplifier polarization state, posted by Ronic Chiche at Optical room about lasers and optics cavity_polar_3e_etage_2A_-_20kW.PNGcavity_polar_3e_etage_3A_-_30kW.PNGcavity_polar_3e_etage_3A_-_33kW.PNG
Message ID: 42     Entry time: Thu Dec 19 09:21:45 2019     In reply to: 40
 Author: Ronic Chiche 
 Status: Fixed 
 Type: info 
 Category: lasers and optics 
 Location: Optical room 
 Title: Optical amplifier polarization state 

polarization state of the cavity at higher power : 20kW, 30kW  and 33kW (slight CEP and alignment optimization) :
the polarization state changes only a little to ~ 87° and is almost linear.

Ronic Chiche wrote:

The polarimeter was giving a strange 50% of DOP of the light coming from the cavity.
we had to calibrate (LONG calibration process with care) the polarimeter to get a proper 100% of DOP !
the polarimeter needs also a good alignment with 2 mirrors, a colimated beam and a max power on photodiode between 0.7 and 0.8 (use electronic gain to adapt the level)

at low power (1.5kW inside cavity), the cavity is almost vertically polarized (89°).

Ronic Chiche wrote:

We placed a PBS + 2 photodiodes (PhD1, PhD2) at the output of the amplifier to check how the polarization of the amplifier changes with power.

example with 2nd stage @ 6A :
PhD1 = 24.7 mV
PhD2 = 8.9 mV
PhD1/PhD2 = 2.78

and with 3rd stage @ 2A :
PhD1 = 353 mV
PhD2 = 82.8 mV
PhD1/PhD2 = 4.26

Conclusion : we must adapt the quarter and half waveplates for each input power to be always matched with cavity polarization !!!
One could also study how the amplifier polarization changes during time and temperature.

 

 

Attachment 1: cavity_polar_3e_etage_2A_-_20kW.PNG  49 kB  | Hide | Hide all
cavity_polar_3e_etage_2A_-_20kW.PNG
Attachment 2: cavity_polar_3e_etage_3A_-_30kW.PNG  49 kB  | Hide | Hide all
cavity_polar_3e_etage_3A_-_30kW.PNG
Attachment 3: cavity_polar_3e_etage_3A_-_33kW.PNG  49 kB  | Hide | Hide all
cavity_polar_3e_etage_3A_-_33kW.PNG
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