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Entry   Cavity Lock and Finess measurment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics 6x
    Reply   Cavity Lock and Finess measurment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics 
       Reply   Cavity Lock and Finess measurment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics Finesse_Fit.png
          Reply   Cavity Lock and Finess measurment , posted by Manar Amer at ThomX igloo about lasers and optics | detectors and electronics apercu_03.jpgBras_manipulateur.jpg
Message ID: 127     Entry time: Fri Feb 4 10:59:56 2022     In reply to: 126
 Author: Manar Amer 
 Status: Fixed 
 Type: report 
 Category: lasers and optics | detectors and electronics 
 Location: ThomX igloo 
 Title: Cavity Lock and Finess measurment  

one thing which could reduce the Finesse is the L-shape metal piece if it is slightly inserted in the FP-cavity mode path.
understanding where this L-shape effectively is is not easy... some pictures are attached.

Manar Amer wrote:

After changing the way of injecting modulation for PDH and modulation for FSR scanning (we split the modulations to 2 different EOMs), the locking is very stable and we can measure the Finesse.

FSR = 33.34MHz

hereafter, the transmission power during an FSR scan and its fit (sweep of 300kHz of FSR in 2s)

we took 5 acquisitions which give a Finesse of :

4236
4254
4400
4045
4177

=> roughly Finesse = 4200 ! far from the 17000 previously obtained........

Manar Amer wrote:

to measure the Finesse, instead of having 2x EOM for the PDH and for the modulation sweep, I simply used 2x generators coupled with DC-blocks to a T connector (SMA) screwed directly on the EOM input.

as the transmission signal is fluctuating, it is not easy to have a good fit of the Airy peak.

if I measure the width at half of the maximum of the peak, I found roughly 10kHz instead of the awaited 2kHz... :-(

one needs a better evaluation with a more stable transmission signal and also to be sure that the L-shape metal piece (used to remove high order modes) does not introduce some losses and then reduce the Finesse...

Manar Amer wrote:

This morning, me and Ronic managed to obtain the FSR and image of the finesse which is to be analyzed.

Adding:

  • Beam Image at P4 propagation, no lens is added.
  • Image of the Finesse on Oscilloscope

more information to be included later

Will continue in the afternoon .

 

 

 

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