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Entry   Locking Amplifier with Cavity , posted by Manar Amer at Optical room about lasers and optics 20220907_00mode.jpg20220907_00mode_diameter.jpgScreenshot_2022-09-07_0_174654.pngScreenshot_2022-09-07_2_182520.png
    Reply   Locking Amplifier with Cavity , posted by Manar Amer at Optical room about lasers and optics 
       Reply   Locking Amplifier with Cavity , posted by Manar Amer at Optical room about lasers and optics Screenshot_2022-09-08_0_133245.png
          Reply   Locking Amplifier with Cavity , posted by Manar Amer at Optical room about lasers and optics Screenshot_2022-09-08_2_144338.png
             Reply   Locking Amplifier with Cavity , posted by Manar Amer at Optical room about lasers and optics 
             Reply   Locking Amplifier with Cavity , posted by Manar Amer at Optical room about lasers and optics 
                Reply   Locking Amplifier with Cavity , posted by Manar Amer at Optical room about lasers and optics Screenshot_2022-09-09_0_120737.png
                   Reply   Locking Amplifier with Cavity , posted by Manar Amer at Optical room about lasers and optics 
Message ID: 153     Entry time: Fri Sep 9 12:49:44 2022     In reply to: 152
 Author: Manar Amer 
 Status: Fixed 
 Type: report 
 Category: lasers and optics 
 Location: Optical room 
 Title: Locking Amplifier with Cavity  

Alignment was improved to ~ 1.2 V on the photodiode.

Only the second stage was on with ~ 1 W output from amplifier

we measured the transmission from S2 to be 2.3 mW

Manar Amer wrote:

image of the lock with Coupling of ~ 60%

 

Manar Amer wrote:

We locked the cavity, and it is stable using the Transmission,

the high frequency that we thought could have a reason for instability, is due to the high power on the photo diode of the PDH box which can cause non-linearity effects in the signal.

We also closed the fan of the third stage and there was no significant change on the error signal and the piezo+AOM compensation signal.  

        

Manar Amer wrote:

We managed to lock the cavity by adding the AOM , but the lock is still difficult to stabilize.

There is some high frequency compensated by the AOM at ~ 170 kHz (yet to understand from where it comes from)

Manar Amer wrote:

We played on the CEP using the USB command "id0=xxxxx" of the Menhir.

we put id0=48650 and we improved A LOT the transmission and coupling (~ 60%)

here is an image of the first attempts to lock... but the locking is quite difficult.
yellow : transmission
green : reflection
amplifier is still with 2nd stage only (Pout=~1W)

we are adding an AOM in the loop...

Manar Amer wrote:

Today, we played on the CEP but using the I-tune input of the Menhir Laser (+/- 5V maximal range).

unfortunately, one only saw a very weak improvement of the transmission by 10-20%... and the coupling improvement is almost zero.

the best improvement was for the maximal I-tune range (+5V) which maybe means that we could improve more the effect if were able to get a full range of 2pi for the CEP (instead of the present pi/2 range).

Manar Amer wrote:

Today we managed to observe the fundamental mode and stabilize the scan on it until we improved the alignment enough.

We see some coupling, but it is very week < 5% , We improved the alignment and the polarization, but there is still no explanation to why it is very low.

The mode shape is circular with radius = 0.89 mm at transmission point, ~ 40 cm from circular mirror.

One EOM was installed along the injection into the amplifier, we saw a drop in the power measured by the first stage monitor from ~ 8.2 mW to 7.2 mW

we improved the injection up to 7.6 mW, but it still fluctuates a lot. We need to be careful about it.

The error signal looks clean, but it is very week which is due to the weak coupling.

 

 

 

 

 

 

 

 

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