[Yamat, nakano]

I haven't measured the frequency noise yet, but we have 130 kHz bandwidth and suppression gain of an additional gain of 30 dB at 10 kHz and 60 dB at 1kHz.

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1. Cabling.

Now the broadband EOM for the phase compensation is cabled to the FAST OUT of the common mode servo with 30 m SMA cable. We also prepared 4*30 m cable between PSL and IOO rack. These cables are for the digitalization of the RefCav and PMC loop. 

 

2. Lock IMC

The IMC was locked with a new control scheme. OLG is shown in the attached figure (simulated and measured) UGF is 130 kHz and the phase margin is almost 30 degrees.

 

Cross over frequency between PZT and EOM loop is 15 kHz. Relative OLG is shown in the attached file. Servo configuration is as shown in the attached figure. MCL loop is also engaged and the cross-over frequency with the PZT loop is 3Hz.

 

3. Laser power adjustment at IMC_REFL PD.

The laser power at the REFL PD was optimized to 50 mW from 1 mW. Therefore, the optical gain was increased by 34dB. The common-mode servo should be operated with positive gain from the view of the servo noise, but the IN1GAIN got negative with the new large optical gain. Therefore, I implemented a 20 dB attenuator at the input of the common mode servo. 

 

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Todos

• Implement the voltage-controlled phase shifter
• Digitalize the RefCav loop (and PMC)
• Optimize the CARM loop with a new faster IMC loop. 
• Frequency noise measurement with the arm cavity.
• Optical gain measurement